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'[TECH] Photography -- depth of field'
2010\05\14@185412
by
Vitaliy
A question for Russell et al. :)
Say you have a small object (about the size of a postage stamp) that you are
trying to photograph at high resolution. You can get it all in focus using a
large aperture setting (say, 14) but it comes out sort of blurry/noisy. When
you use a small aperture setting (say, 4) you can get really sharp details,
but the depth of field is so narrow, that in 3/4 view you can only get a
part of the object in focus.
Of course, you can move the camera back, but then you don't get the high
resolution.
Short of photographing the front, middle, and back, and stitching them
together in Photoshop, what are the options?
Thank you in advance.
Vitaliy
2010\05\14@190123
by
William \Chops\ Westfield
On May 14, 2010, at 3:53 PM, Vitaliy wrote:
> You can get it all in focus using a large aperture setting (say, 14)
> but it comes out sort of blurry/noisy.
Really? Most lenses are sharper at the higher F-stop. It sounds
vaguely like your camera's automatic modes are increasing ISO setting
and shutter-open time to accommodate the f-stop, but causing noise and/
or motion blur in the process. You can try:
Mount camera on a tripod.
Increase illumination.
Lock ISO settings.
Set full manual exposure.
Use a remote shutter release or the self-timer to eliminate the camera
shake that happens when you push the button.
BillW
2010\05\14@193230
by
cdb
2010\05\14@203101
by
Marechiare
> Of course, you can move the camera back, but then
> you don't get the high resolution.
If I am not mistaken, you were advised a year ago to give a try to
"Zoom" button. If your camera's zoom does not work well in macro mode,
you may either get the right camera or just use an external lens. Good
luck.
2010\05\14@203253
by
Olin Lathrop
Vitaliy wrote:
> Say you have a small object (about the size of a postage stamp) that
> you are trying to photograph at high resolution. You can get it all in
> focus using a large aperture setting (say, 14) but it comes out sort of
> blurry/noisy. When you use a small aperture setting (say, 4) you can
> get really sharp details, but the depth of field is so narrow, that in
> 3/4 view you can only get a part of the object in focus.
>
> Of course, you can move the camera back, but then you don't get the high
> resolution.
>
> Short of photographing the front, middle, and back, and stitching them
> together in Photoshop, what are the options?
Your aperture values are confusing, or you're confused. If by "aperture
setting", you mean what is common referred to as a F-stop, then 14 is a
strange number (normal F stops come in multiples of sqrt(2)) and "F" 14 is
actually a smaller aperture than "F" 4. This is why I always write it as
f/14 and f/4, and that's also what you'll see written wherever people
actually know what they're taking about. This literally denotes a fraction
of the focal length, since "f" stands for the focal length of the lens.
If the aperture were a perfect disc, then f/xx is literally the diameter of
that disk. For example, if your lens has a focal length of 50mm and you set
it to a aperture of f/4, then the effective diameter of the lens element if
it were a single element lens would be 12.5mm. The amount of light let thru
by the lens is proportional to its area, which is why common F-stops (2.0,
2.8, 4.0, 5.6, 8, 11, 16, ...) come in multiples of sqrt(2). Each
successive F-stop changes the diameter by sqrt(2), which changes the light
let thru by 2.
Anyway, back to your question. At the small aperture of f/14 you get
sufficient depth of field but the image is noisy, whereas at the large
aperture of f/4 the noise is gone but the depth of field is insufficient.
This makes perfect sense for a somewhat dumbed down electronic camera or a
fancy electronic camera in a unfortunate "program" mode.
Here's my guess what's happening. You have relatively low light on the
subject. When you tell the camera to use f/14 that cuts down the available
light even more. The camera is compensating automatically by switching to a
higher sensitivity setting for its imaging array. Even low end cameras
nowadays have "ISO" settings like 100, 400, 800, 1600, and possibly more.
At low values the sensor needs more light to fully expose the image, but has
better signal to noise ratio. At higher settings, it's more sensitive but
provides a lower signal to noise ratio.
At f/14 you're getting the large depth of field because that's just a
function of the lens geometry. The camera sees there is little light and
switches to the high sensitivity setting to give you something other than a
black or muddy picture, but you also get the noise. At f/4 the lens lets
enough light thru so that the sensor can be used in less sensitive mode with
less noise.
There are several solutions. The simplest brute force approach is to try it
again outside in the Phoenix sun at noon. That's most likely several orders
of magnitude more light than anything you did indoors. It's also a much
better color mix of light. The extra light will do wonders for the camera's
tradeoff, and all will be fine.
Another solution, depending on your camera, is to force it to use a long
exposure. Some dumbed down point and shoot cameras can't be told to do
that, but at the least there will be a few different program modes to choose
from. Unfortunately these tend to have stupid names that don't really tell
you what tradeoffs they cause, but things like "museum" will be much better
for this than "sport". Your camera manual may tell you what tradeoffs
different modes have, depending on how dumb they think you are.
To do this right, you will need to make sure the camera is held still for
the duration of the shot, which could be over a second. That's what a
tripod is for, but clamped down or even taped against something fixed and
rigid will work. The real point is that nobody must be touching the camera
during exposure. No matter how still you can hold your hand in human terms,
it won't be still enough for this purpose. You may have to use the self
timer only so that your finger is off the camera and therefore no longer
shaking it when the picture is taken. This is also what a cable release is
for, but then again anyone that has a tripod and a cable release wouldn't be
asking this question.
********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014. Gold level PIC consultants since 2000.
2010\05\14@203719
by
Olin Lathrop
cdb wrote:
> Would buying a Macro lens be in order?
No. He already said that it is possible to fill the frame with the desired
image. The real problem is light and sensitivity setting, neither of which
macro has anything to do with. The only difference between a macro lens and
a "normal" lens is that the macro lens is mechanically set up to allow it to
move further from the camera, thereby allowing it to focus on things closer
to the camera. This effects a some other tradeoffs in the lens design, but
these are irrelevant for this purpose. The lens still works like a lens,
just focuses closer.
********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014. Gold level PIC consultants since 2000.
2010\05\14@203843
by
William \Chops\ Westfield
On May 14, 2010, at 3:53 PM, Vitaliy wrote:
> Short of photographing the front, middle, and back, and stitching
> them together in Photoshop
BTW, there are apparently some utilities to do this automatically or
semi-automatically.
http://chdk.wikia.com/wiki/DoF_Stacking
2010\05\14@221533
by
Vitaliy
"cdb" wrote:
> Would buying a Macro lens be in order?
>
> There are also the pseudo macro lenses such as extenders that fit
> between the lens and the camera, cheaper, but possibly doesn't provide
> such a sharp phtotograph.
>
> Is this a digital or film camera?
Canon DigitalRebel XT w/ a macro lens.
Vitaliy
2010\05\14@221646
by
Vitaliy
Marechiare wrote:
>> Of course, you can move the camera back, but then
>> you don't get the high resolution.
>
> If I am not mistaken, you were advised a year ago to give a try to
> "Zoom" button. If your camera's zoom does not work well in macro mode,
> you may either get the right camera or just use an external lens. Good
> luck.
You are mistaken.
2010\05\14@221912
by
Vitaliy
"William "Chops" Westfield wrote:
>> You can get it all in focus using a large aperture setting (say, 14)
>> but it comes out sort of blurry/noisy.
>
> Really? Most lenses are sharper at the higher F-stop.
Not true, you get more of the image in focus but you get a sharper image at
the lower F-stop settings.
> It sounds
> vaguely like your camera's automatic modes are increasing ISO setting
> and shutter-open time to accommodate the f-stop, but causing noise and/
> or motion blur in the process. You can try:
>
> Mount camera on a tripod.
Check.
> Increase illumination.
Plenty of light sources all around, and very close to the object.
> Lock ISO settings.
Check.
> Set full manual exposure.
Check.
> Use a remote shutter release or the self-timer to eliminate the camera
> shake that happens when you push the button.
The remote shutter is permanently attached to the camera. Can't remember the
last time we used the button.
Vitaliy
2010\05\14@223918
by
Vitaliy
|
Olin Lathrop wrote:
> Your aperture values are confusing, or you're confused.
Based on the content of your email I'd say you are the one who's confused,
and I fail to understand why. What is the alternative to the F-stop?
> If by "aperture
> setting", you mean what is common referred to as a F-stop,
Duh?
> .. then 14 is a
> strange number (normal F stops come in multiples of sqrt(2)) and "F" 14 is
> actually a smaller aperture than "F" 4. T
It may be strange to you, but it is what it is. I can send you a RAW image
if you are eager to check the metadata to confirm the fact.
> ..this is why I always write it as
> f/14 and f/4, and that's also what you'll see written wherever people
> actually know what they're taking about. This literally denotes a fraction
> of the focal length, since "f" stands for the focal length of the lens.
Are those the same experts who used a phone cam to take the pictures for the
Embed Inc. website? ;)
{Quote hidden}> If the aperture were a perfect disc, then f/xx is literally the diameter
> of
> that disk. For example, if your lens has a focal length of 50mm and you
> set
> it to a aperture of f/4, then the effective diameter of the lens element
> if
> it were a single element lens would be 12.5mm. The amount of light let
> thru
> by the lens is proportional to its area, which is why common F-stops (2.0,
> 2.8, 4.0, 5.6, 8, 11, 16, ...) come in multiples of sqrt(2). Each
> successive F-stop changes the diameter by sqrt(2), which changes the light
> let thru by 2.
Wow.
{Quote hidden}> Anyway, back to your question. At the small aperture of f/14 you get
> sufficient depth of field but the image is noisy, whereas at the large
> aperture of f/4 the noise is gone but the depth of field is insufficient.
> This makes perfect sense for a somewhat dumbed down electronic camera or a
> fancy electronic camera in a unfortunate "program" mode.
>
> Here's my guess what's happening. You have relatively low light on the
> subject. When you tell the camera to use f/14 that cuts down the
> available
> light even more. The camera is compensating automatically by switching to
> a
> higher sensitivity setting for its imaging array. Even low end cameras
> nowadays have "ISO" settings like 100, 400, 800, 1600, and possibly more.
> At low values the sensor needs more light to fully expose the image, but
> has
> better signal to noise ratio. At higher settings, it's more sensitive but
> provides a lower signal to noise ratio.
>
> At f/14 you're getting the large depth of field because that's just a
> function of the lens geometry. The camera sees there is little light and
> switches to the high sensitivity setting to give you something other than
> a
> black or muddy picture, but you also get the noise. At f/4 the lens lets
> enough light thru so that the sensor can be used in less sensitive mode
> with
> less noise.
All of your guesses are based on the assumption that my photographer and I
are morons. So your suggested solutions below are useless. Thank you for the
effort.
{Quote hidden}> There are several solutions. The simplest brute force approach is to try
> it
> again outside in the Phoenix sun at noon. That's most likely several
> orders
> of magnitude more light than anything you did indoors. It's also a much
> better color mix of light. The extra light will do wonders for the
> camera's
> tradeoff, and all will be fine.
>
> Another solution, depending on your camera, is to force it to use a long
> exposure. Some dumbed down point and shoot cameras can't be told to do
> that, but at the least there will be a few different program modes to
> choose
> from. Unfortunately these tend to have stupid names that don't really
> tell
> you what tradeoffs they cause, but things like "museum" will be much
> better
> for this than "sport". Your camera manual may tell you what tradeoffs
> different modes have, depending on how dumb they think you are.
>
> To do this right, you will need to make sure the camera is held still for
> the duration of the shot, which could be over a second. That's what a
> tripod is for, but clamped down or even taped against something fixed and
> rigid will work. The real point is that nobody must be touching the
> camera
> during exposure. No matter how still you can hold your hand in human
> terms,
> it won't be still enough for this purpose. You may have to use the self
> timer only so that your finger is off the camera and therefore no longer
> shaking it when the picture is taken. This is also what a cable release
> is
> for, but then again anyone that has a tripod and a cable release wouldn't
> be
> asking this question.
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts,
http://www.embedinc.com/products
> (978) 742-9014. Gold level PIC consultants since 2000.
> --
2010\05\14@224632
by
Vitaliy
William "Chops" Westfield wrote:
>> Short of photographing the front, middle, and back, and stitching
>> them together in Photoshop
>
> BTW, there are apparently some utilities to do this automatically or
> semi-automatically.
> http://chdk.wikia.com/wiki/DoF_Stacking
The trouble is, when we focus on the different parts, the object "moves" in
each snapshot. Our designer is amazing though, he already stitched it
together so you can't even tell where the seams are (I will post the image
once he's done touching it up). It's a lot of work, however, that we'd like
to avoid having to do in the future.
We tried a bunch of things, including a different (non-macro) lens. I guess
I'll have to wait for Russell to come back with a magic solution.
Vitaliy
2010\05\14@230233
by
Roger Kadau
Methinks you are using 1.4 as the large aperture setting rather than 14.
On Fri, May 14, 2010 at 6:53 PM, Vitaliy <.....piclistKILLspam
@spam@maksimov.org> wrote:
> A question for Russell et al. :)
>
> Say you have a small object (about the size of a postage stamp) that you are
> trying to photograph at high resolution. You can get it all in focus using a
> large aperture setting (say, 14) but it comes out sort of blurry/noisy. When
> you use a small aperture setting (say, 4) you can get really sharp details,
> but the depth of field is so narrow, that in 3/4 view you can only get a
> part of the object in focus.
>
2010\05\14@230858
by
Vitaliy
Meknows you are mistaken.
----- Original Message -----
From: "Roger Kadau" <rekKILLspamemail.com>
To: "Microcontroller discussion list - Public." <.....piclistKILLspam.....mit.edu>
Sent: Friday, May 14, 2010 20:02
Subject: Re: [TECH] Photography -- depth of field
{Quote hidden}> Methinks you are using 1.4 as the large aperture setting rather than 14.
>
> On Fri, May 14, 2010 at 6:53 PM, Vitaliy <
EraseMEpiclistspam_OUTTakeThisOuTmaksimov.org> wrote:
>> A question for Russell et al. :)
>>
>> Say you have a small object (about the size of a postage stamp) that you
>> are
>> trying to photograph at high resolution. You can get it all in focus
>> using a
>> large aperture setting (say, 14) but it comes out sort of blurry/noisy.
>> When
>> you use a small aperture setting (say, 4) you can get really sharp
>> details,
>> but the depth of field is so narrow, that in 3/4 view you can only get a
>> part of the object in focus.
>>
> --
2010\05\14@233938
by
Roger Kadau
OK, if it's f/14 that you are using, that would be a smaller aperture
than f/4 and the symptoms that you label blurry/noisy would actually
be diffraction. More light would not make this go away. You would
either need a larger sensor or a larger aperture, which unfortunately
gives you less depth of field.
On Fri, May 14, 2010 at 11:07 PM, Vitaliy <piclistspam_OUTmaksimov.org> wrote:
> Meknows you are mistaken.
>
> ----- Original Message -----
> From: "Roger Kadau" <@spam@rekKILLspamemail.com>
>
>> Methinks you are using 1.4 as the large aperture setting rather than 14.
2010\05\14@234259
by
William \Chops\ Westfield
On May 14, 2010, at 7:17 PM, Vitaliy wrote:
>> Most lenses are sharper at the higher F-stop.
>
> Not true, you get more of the image in focus but you get a
> sharper image at the lower F-stop settings.
Heh. Certainly not true for high-speed telephotos... Though most
lenses do best in the middle of their range rather than at either
extreme.
Aperture setting descriptions are a bit ambiguous; smaller numbers
mean bigger lens openings and less depth of field, bigger numbers mean
smaller openings and greater depth of field (by this time it is quite
clear that Vitaliy and his photographer DO understand this. To be
fair to Olin, you didn't give much info in the original message as to
your level of expertise or what steps had already been tried...)
I've never heard of macro photography issues where pictures got
noisier at higher F-stops, but I suppose it makes some sense that
you'd get more noise in a longer exposure.
BillW
2010\05\14@234805
by
Roger Kadau
|
I'm sorry, I don't think I was quite clear. If you use a larger
aperture you won't have the problem with diffraction but your depth of
field decreases. But, if you can get a camera with a larger sensor you
may be able to use that smaller aperture f/14 and not have the problem
with diffraction and keep the greater depth of field.
On Fri, May 14, 2010 at 11:39 PM, Roger Kadau <KILLspamrekKILLspamemail.com> wrote:
{Quote hidden}> OK, if it's f/14 that you are using, that would be a smaller aperture
> than f/4 and the symptoms that you label blurry/noisy would actually
> be diffraction. More light would not make this go away. You would
> either need a larger sensor or a larger aperture, which unfortunately
> gives you less depth of field.
>
> On Fri, May 14, 2010 at 11:07 PM, Vitaliy <
RemoveMEpiclistTakeThisOuTmaksimov.org> wrote:
>> Meknows you are mistaken.
>>
>> ----- Original Message -----
>> From: "Roger Kadau" <
spamBeGonerekspamBeGoneemail.com>
>
>>
>>> Methinks you are using 1.4 as the large aperture setting rather than 14.
>
2010\05\15@002407
by
Russell McMahon
Rushing so super brief (for me).
Much good advice. Quite a lot of what Olin said was quite good and as he
didn't know what you knew he over-explained things for your level of
knowledge. I think that your response will probably ensure that he won't do
that again. His suggestions re the camera attempting to increase sensitivity
may well be right and his comments re bright sunlight are also good.
His comments on std f numbers used was correct and almost invariably what
was used with film. Some digital cameras use random f stops and shutter
speeds which annoys long time photographer brains - like eg mine.
Knowing what camera you are using and what lens (if separable) would be
useful.
Knowing light source and intensity also helps.
Depth of focus can be calculated for a given aperture and distance. Gargoyle
knows. (Too rushed ot I'd dig it up).
There will be an optimum point part way along the length to centre your
focus on for best result. Probably / maybe at the geometric mean distance.
If I was doing this I'd us widest aperture where diffraction was not a major
factor. f 1:22 is usually OK. f 1:16 certainly so (with APSC DSLR - I think
this translates directly with other systems but may need to think more on
that).
Higher ISO will produce more noise. Camera may "ISO up" automatically.
Shutter speed will drop as aperture increases for given light level.
It's easy to drop into areas where shake matters. You are probably using a
tripod but just in case - use a tripod.
If the camera and/or lens has anti-shake and you are using a tripod, turn
the anti-shake off - the servo tries to hunt for noise and there is none but
it effectively makes some.
For a given aperture shorter focal lengths and closer up should give more
depth of field than further away and long focal length to compensate.
If this were I, I'd start at:
1. Play:
- Brightest light. Sun is 100,000 + lux on good day. Photofloods usually
less.
- Low ISO <= 200. Lower possibly.
- f22 to start
- tripod
- antishake off.
- focus near geometric mean.
- play with focal length.
Similar shots at f 8 11 16 22 32 should see depth of focus improve up to
f16, probably Ok at f22, odds are f32 will be diffraction affected.
2. Calculate what theory says I SHOULD be able to achieve (after having
failed :-) ).
Russell
2010\05\15@012731
by
William \Chops\ Westfield
On May 14, 2010, at 8:42 PM, William Chops Westfield wrote:
> I've never heard of macro photography issues where pictures got
> noisier at higher F-stops, but I suppose it makes some sense that
> you'd get more noise in a longer exposure.
Hmm. One thing that I've seen suggested elsewhere that may help is to
forget about trying to fill the frame with the object in question,
move the camera further away, and then crop the final image to
appropriate borders. A modern digital camera has plenty of pixels to
be able to afford post-exposure cropping, and actual depth of field is
a function of distance from the lens as well as f-stop and focal length.
(This is usually advice to people who end up with out-of-focus
pictures because they have no macro mode at all, and an in-focus
picture with 1MP is more useful than an out-of-focus 8MP image,
especially if it's going to be shrunk to a webpage anyway. It may not
be applicable to your situation. Then again, it might be worth a try.)
BillW
2010\05\15@041800
by
cdb
2010\05\15@043232
by
Russell McMahon
> Canon DigitalRebel XT w/ a macro lens.
f 1:22, ISO200, brightest light, tripod, no antishake, focus 1/3 way
from front to back, lower than higher focal length.
I'm getting several inches of reasonably crisp focus with an APSC
sensor A700 Sony and non macro Sony 18-250 lens.
What size is the final image required to be and what sort of quality
(apart from sharpness).
Can you describe the target well enough to allow it to be emulated. ?
Would eg a row of 6 or 8 point font imaged at 30 degrees to horizontal
or at 45 degrees suffice as a comparison?
Russell
2010\05\15@044113
by
Michael Watterson
William "Chops" Westfield wrote:
> Hmm. One thing that I've seen suggested elsewhere that may help is to
> forget about trying to fill the frame with the object in question,
> move the camera further away, and then crop the final image to
> appropriate borders. A modern digital camera has plenty of pixels to
> be able to afford post-exposure cropping, and actual depth of field is
> a function of distance from the lens as well as f-stop and focal length.
>
> (This is usually advice to people who end up with out-of-focus
> pictures because they have no macro mode at all, and an in-focus
> picture with 1MP is more useful than an out-of-focus 8MP image,
> especially if it's going to be shrunk to a webpage anyway. It may not
> be applicable to your situation. Then again, it might be worth a try.)
>
> BillW
>
>
I think of Microscopes (terrible depth of field) vs cheap camera
(anything more than 4m is "infinity" and in focus),
I think macro mode inherently (though I wrecked my head years ago
trying the sums) has poor depth of field. The above suggestion may
be best.
Go to non-macro and wide angle and only close enough to get enough pixels.
I suspect (but I can't do the sums to prove it) that 35mm film frame
size sensor vs 1/4" sensor or 110 film camera that the smaller image
area has more depth of field.
I don't think there is an easy solution.
I think closing the aperture only increases the sharpness at the focused
distance, and only up to a certain point (maybe about f/8 on standard
less 35mm camera), depending on lens design, then the aperture creates
"circles of confusion" and maybe by f/22 starts to act as an obvious
lens element. Certainly this is why in very bright conditions you need a
neutral density filter and avoid tiny apertures (say f/8 to f/11 as limit)?
I never figured how to get decent depth of field taking pictures of
insects other than further away and only filling about 1/5th of frame,
good film and then crop later. (OM10 and large selection of lens, also
in days of yore a Zenit and extension tubes between camera and lens)
2010\05\15@090923
by
Olin Lathrop
Vitaliy wrote:
>>> You can get it all in focus using a large aperture setting (say, 14)
>>> but it comes out sort of blurry/noisy.
>>
>> Really? Most lenses are sharper at the higher F-stop.
>
> Not true, you get more of the image in focus but you get a sharper
> image at the lower F-stop settings.
Not really true either. There are several interacting and competing factors
going on here.
First, no lens is perfect. And even if you could get a optically perfect
lens, this perfection only holds true for the center of the image. There
are some inherent distortions as you get away from the center. Like
anything, real lenses are a series of compromises (hopefully) cleverly
traded off by skilled engineers. The compromises to off center and other
tradeoffs get worse with wider aperture.
Second, there is such a thing as "single slit diffraction". Every
electromagnetic wave will bend a little as it passes near objects, with
"near" being related to the wavelength. Another way to put this is that
there is no such thing as a sharp shadow. Even if the thing making the
shadow is perfectly sharp and straight, the light waves are not simply
blocked on one side of a mathematical line and passed on the other. They
are bent to varying degrees near the obstruction. The wavelength of visible
light is so small that we normally don't see this effect at human-size
scale. AM radio is a good example of this effect put to use. The earth is
the obstruction, and the the "ground" wave will bend with the curvature of
the earth so that you can receive transmission even though the earth is
blocking the direct line between the transmitter and your radio.
There are other effects too I won't go into. The net result is that for
most lenses there is a arpeture setting where the sum of these effects is
minimum and you get the best "sharpness" (a term that by itself is a lot
more complicated to quantify than you may think). For common camera lenses,
f/8 is usually a good guess for best sharpness if you don't have specific
data.
********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014. Gold level PIC consultants since 2000.
2010\05\15@092858
by
Olin Lathrop
Vitaliy wrote:
> Based on the content of your email I'd say you are the one who's
> confused, and I fail to understand why. What is the alternative to
> the F-stop?
The confusion was because you referred to "14" as a larger aperture than
"4". That means either these are not common F-stop values or you are
confused, since high F-stop values actually mean a smaller arpeture.
> It may be strange to you, but it is what it is. I can send you a RAW
> image if you are eager to check the metadata to confirm the fact.
No, f/14 is unusual, but there is nothing wrong about it. I was trying to
make sure you really meant this and there wasn't something else going on.
Like when debugging a PIC program, you look for little things that just
don't seem right. Sometimes they are right after further investigation.
However, it might be useful to show the two pictures you describe. This is
not to verify the arpeture setting, but to see the nature of the distortions
and noise. These are hard to describe in words, and the true problem may be
easier to diagnose when the symptoms can be carefully examined.
{Quote hidden}>> Anyway, back to your question. At the small aperture of f/14 you get
>> sufficient depth of field but the image is noisy, whereas at the
>> large aperture of f/4 the noise is gone but the depth of field is
>> insufficient. This makes perfect sense for a somewhat dumbed down
>> electronic camera or a fancy electronic camera in a unfortunate
>> "program" mode.
>>
>> Here's my guess what's happening. You have relatively low light on
>> the subject. When you tell the camera to use f/14 that cuts down the
>> available
>> light even more. The camera is compensating automatically by
>> switching to a
>> higher sensitivity setting for its imaging array. Even low end
>> cameras nowadays have "ISO" settings like 100, 400, 800, 1600, and
>> possibly more. At low values the sensor needs more light to fully
>> expose the image, but has
>> better signal to noise ratio. At higher settings, it's more
>> sensitive but provides a lower signal to noise ratio.
>>
>> At f/14 you're getting the large depth of field because that's just a
>> function of the lens geometry. The camera sees there is little
>> light and switches to the high sensitivity setting to give you
>> something other than a
>> black or muddy picture, but you also get the noise. At f/4 the lens
>> lets enough light thru so that the sensor can be used in less
>> sensitive mode with
>> less noise.
>
> All of your guesses are based on the assumption that my photographer
> and I are morons. So your suggested solutions below are useless.
> Thank you for the effort.
Not morons, but unfamiliar with some of the details and physics of
photography. After all, you did ask, and you demonstrated some confusion
about arpetures or at least how they are communicated, so I think this is a
justified assumption.
Instead of just dismissing my explanation and suggestions because you think
that I think you're a moron, I'd like to hear at least why specifically you
think my explanation is wrong and therefore the suggestions ineffective. So
far you have provided no facts that refute my guess as to what is going on,
only unwarrented insults.
2010\05\15@093512
by
Olin Lathrop
Roger Kadau wrote:
> I'm sorry, I don't think I was quite clear. If you use a larger
> aperture you won't have the problem with diffraction but your depth of
> field decreases. But, if you can get a camera with a larger sensor you
> may be able to use that smaller aperture f/14 and not have the problem
> with diffraction and keep the greater depth of field.
I'm guessing he's not seeing diffraction effects as much as sensor noise.
Diffraction is a rather subtle effect, and unlikely to be a major issue at
f/14. I'd really like to see the f/15 picture though. That would clarify a
lot about what is really going on.
********************************************************************
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(978) 742-9014. Gold level PIC consultants since 2000.
2010\05\15@094708
by
Olin Lathrop
Michael Watterson wrote:
> I suspect (but I can't do the sums to prove it) that 35mm film
> frame size sensor vs 1/4" sensor or 110 film camera that the smaller
> image area has more depth of field.
It doesn't work that way. Absolute size doesn't matter. Depth of field is
governed by a set of ratios.
********************************************************************
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(978) 742-9014. Gold level PIC consultants since 2000.
2010\05\15@103519
by
Marechiare
> I'm guessing he's not seeing diffraction effects as much
> as sensor noise. Diffraction is a rather subtle effect, and
> unlikely to be a major issue at f/14.
I'm afraid, diffraction could be the major issue at f/14. Though I
must admit I got no experience in this area and I don't plan getting
any.
2010\05\15@112314
by
Russell McMahon
>From below
DOF in mm ~= Stop x distance / Focal length / 2
DOF in inches ~= Stop x distance / Focal length / 50
For distance to subject and focal length in consistent units but which
do not have to be the units that DOF is stated in :-).
DOF is smaller for people with good eyes or in brighter light!!!
E&OE !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
===================================================
>> I'm guessing he's not seeing diffraction effects as much
>> as sensor noise. Diffraction is a rather subtle effect, and
>> unlikely to be a major issue at f/14.
> I'm afraid, diffraction could be the major issue at f/14. Though I
> must admit I got no experience in this area and I don't plan getting
> any.
I find I can typically use f22 without noticeable diffraction
softening. It's probably there but largely swamped by other issues in
the lens class I deal with. [Approaching OK by my standards, more than
expensive enough by my wife's standards, far short of what the
professionals usually buy with perhaps one exception].
f32 works and can be sharper than with a larger aperture in some cases.
Mr Wikipedia says:
When the depth of focus relates to a single plane in object space, it
can be calculated from[1]
DOF = t = 2 N C V / f
where t is the total depth of focus, N is the lens f-number, c is the
circle of confusion, v is the image distance, and f is the lens focal
length. In most cases, the image distance is not easily determined;
"Circle of confusion" ~~~= largest area you perceive by eye as a point
and not a finite sized spot.
Thus COC is subjective depending on observer, lighting and viewing distance.
A typical value is 0.2mm based on a typical viewer viewing an image at
250 mm and resolving 5 line pairs per mm. The size of image which is
comfortably viewed at that distance is determined by viewing angle
being 60 degrees max and is about an 8x10" or A4 print.
SO DOF = 10 x f_stop x image distance / focal length.
So DOF increases linearly with f_stop( decreasing aperture), greater
image distance, decreasing focal length.
For say f 1:16, 50mm Focal Length , coc = 0.2mm
DOF = 2 x fstop x COC x Distance / Focal length *
DOF =~~ Distance / 8
So for Vitaliy to get 1" DOF he needs about 8" distance from object.
Image size will be set by above parameters + distance.
Double f = double DOF
Double distance = double DOF BUT area of image will decrease x 4 times !
Halve focal length = double dof.
To get large image size you want to focus at minimum distance at the
focal length of choice and then control aperture.
******************************************************************
* Usefully:
DOF ~~~ 2 x fstop x 0.2 x Distance / Focal length. mm
or
DOF = Stop x distance / Focal length / 2 millimetres
= Stop x distance / Focal length / 50 inches
**********************************************************************
Sanity check.
f16, 8 inches = 200 mm, 50mm lens
DOF = 16 x 200 /50/2 = 32 mm ~~~~= 1 inch as above.
More accurate than that is not possible due to the immense uncertainty
from the COC.
Russell
the depth of focus can also be given in terms of magnification m:
2010\05\15@121257
by
mcd
|
|
This isn't that hard, but it requires a little patience and attention to
detail.
Most modern cameras will focus pretty close. OK, maybe the $20 Wal-Mart
specials won't, but most middle of the road cameras will focus down to a
few inches.
You need to stop down to a small aperature (high f number) to get depth of
field. Most modern digital cameras will suffer some if you allow the
automatic ISO setting to get high. If you can, set the ISO to the lowest
number possible. This is a bad combination because even with bright
lights, the exposure time is likely to get long. Unless your camera has
an unusually small sensor, or you can stop down to f/64, diffraction won't
be an issue.
Don't use the flash. Place bright lights, preferably soft lights (use a
handkerchief), on either side of the subject, off center. I have one of
those nice little ring lights which it just about useless for electronic
stuff because it guarantees bad reflections. Reflections are a far bigger
problem than focus.
Put the camera on a tripod. Exposures are likely to be along the lines of
several seconds. With today's small, lightweight cameras, you cannot hold
it still even at 1/30th of a second. You must use a tripod.
Remember that your autofocus takes a second or two, and activates when you
have pressed the shutter release partway down. Squeeze the shutter
gently, wait for the camera to focus, then go the rest of the way, gently.
Your autofocus mechanism needs something contrasty to focus on. If you
don't have some nice bright silk screening in the focus area of your
camera, place a toothpick or piece of paper in the field (at the right
depth) while it focuses, then pull it away after the focus is set. Better
yet, focus manually if your camera allows.
Best is to use a cable release. Since most modern cameras don't provide
for this, and besides, even if it did you probably don't have one, use the
self timer. Start the timer then move away from the camera so you don't
jostle it during the exposure. Usually the focus is set before the timer
starts, so you still need to be sure you are in focus.
Modern cameras expect to be looking at people, with sky and grass behind
them. When photographing most electronic stuff, the exposures are likely
to be off. Bracket your exposure generously. If you have the choice, it
can also help to bracket the white balance. You're not paying for film
and developing anyway, so if it takes a couple dozen shots to get the one
you want, so what?
Hope this helps.
--McD
2010\05\15@124226
by
Marechiare
>>> I'm guessing he's not seeing diffraction effects as much
>>> as sensor noise. Diffraction is a rather subtle effect, and
>>> unlikely to be a major issue at f/14.
>
>> I'm afraid, diffraction could be the major issue at f/14. Though I
>> must admit I got no experience in this area and I don't plan getting
>> any.
>
> I find I can typically use f22 without noticeable diffraction
> softening. It's probably there but largely swamped by other issues in
> the lens class I deal with.
Interesting, did anybody try using something kind of The Questar
3-1/2” Maksutov for the purpose?
(Maksutov, not Maksimov :-)
2010\05\15@131526
by
Marechiare
>> I'm afraid, diffraction could be the major issue at f/14. Though I
>> must admit I got no experience in this area and I don't plan getting
>> any.
>
> I find I can typically use f22 without noticeable diffraction
> softening. It's probably there but largely swamped by other issues in
> the lens class I deal with.
Somewhat better lenses:
http://www.questarcorporation.com/QuestarPDF/QM_100_30003.pdf
Operating range of f/no: 6.0 to 3.5 (less than 14 or 22)
2010\05\15@132657
by
Russell McMahon
> http://www.questarcorporation.com/QuestarPDF/QM_100_30003.pdf
>
> Operating range of f/no: 6.0 to 3.5 (less than 14 or 22)
Those figures are the maximum possible aperture (= minimum aperture
number) at varous distances. Smaller apertures can usually be used in
practice at any given distance - just not larger ones.
Russell
2010\05\15@183532
by
Marechiare
>> www.questarcorporation.com/QuestarPDF/QM_100_30003.pdf
>>
>> Operating range of f/no: 6.0 to 3.5 (less than 14 or 22)
>
> Those figures are the maximum possible aperture (= minimum
> aperture number) at varous distances. Smaller apertures can
> usually be used in practice at any given distance - just not
> larger ones.
Yes, but that was not a telescope, that was a microscope; there was no
need to catch as much light as possible (at least for that price). The
very reason for the existence of the big apertures must be - better
resolution, I believe. My point (possibly wrong) was that "diffraction
could be the major issue at f/14", not to say at f/22.
BTW, regarding the word "existence", I wonder, does Olin have some
relation to the manufacture Questar? On their main page
http://www.questarcorporation.com/questar.htm they show strange usage
of the word "existence" - "existAnce" in the first sentence, pretty
much complimentary to his usage "impedEnce" :-)
2010\05\15@193527
by
Olin Lathrop
Marechiare wrote:
> Yes, but that was not a telescope, that was a microscope; there was no
> need to catch as much light as possible (at least for that price).
Catching more light, all else being equal, is a good thing in just about any
photographic application.
> The
> very reason for the existence of the big apertures must be - better
> resolution, I believe.
No. Bigger apertures allow for more light gathering. More data on whatever
you're measuring is usually a good thing. It costs money to make optics
larger, whereas cutting down the light is relatively simple and cheap.
Therefore manufacturers brag about the largest apertures a lens can have.
When you buy a telephoto lens, the f/4 ones are going to cost more than the
f/5.6 ones, and the f/2.8 ones will be hideously expensive or nonexistant.
Even at 300mm focal length, a f/2.8 lens would require a optical diameter of
107mm (4.2 inches). That's a big and therefore very expensive piece of
glass to get just right.
> My point (possibly wrong) was that "diffraction
> could be the major issue at f/14", not to say at f/22.
Several people have now told you that diffraction effects don't effectively
matter until at least around f/22. Why do you persist with this point
especially since you said you're not that familiar with this issue?
There is only one way I've found to have diffraction effects visible in the
final picture at lower F stops. That is with lots of extension tubes. For
example, I have a very nice 135mm lens. I did some experiments with it at
1:1 magnification and a little beyond, and the results were washed out even
at apertures as wide as f/11. Note that this lens was not designed for
macro use. I also didn't flip it around, which possibly would have helped
(I didn't have the necessary mounting adapters and didn't feel like rigging
up something for that test).
********************************************************************
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(978) 742-9014. Gold level PIC consultants since 2000.
2010\05\15@200148
by
William \Chops\ Westfield
On May 15, 2010, at 3:35 PM, Marechiare wrote:
>>> www.questarcorporation.com/QuestarPDF/QM_100_30003.pdf
>>>
>>> Operating range of f/no: 6.0 to 3.5 (less than 14 or 22)
>>
>> Those figures are the maximum possible aperture
Actually, since it's a Cassegrain (mirror) design, it doesn't have an
adjustable aperture, so I don't think the comparison to regular optics
(in terms of sharpness@f-stop) makes much sense...
Here's a resolution test of an actual glass macro lens...
http://www.photozone.de/canon-eos/167-canon-ef-100mm-f28-usm-macro-test-report--review?start=1
2010\05\15@202127
by
Marechiare
|
William "Chops" Westfield <RemoveMEwestfwTakeThisOuTmac.com> wrote:
> Here's a resolution test of an actual glass macro lens...
> http://www.photozone.de/canon-eos/167-canon-ef-100mm-f28-usm-macro-test-report--review?start=1
Yes, thanks, and the point of the test was:
***
MTF (resolution)
The lens reaches its peak performance at f/5.6. You shouldn't stop
down beyond f/16 due to the limiting effects of light diffraction.
***
It clearly points out "You shouldn't stop down beyond f/16 due to the
limiting effects of light diffraction." That's why I persist with my
point.
The test contradicts to Olin's: "Several people have now told you that
diffraction effects don't effectively matter until at least around
f/22. Why do you persist with this point especially since you said
you're not that familiar with this issue?"
If at consumer level lenses you "shouldn't stop down beyond f/16 due
to the limiting effects of light diffraction", than with NASA-level
"Maksutov" (sorry, I did not find "Cassegrain" mentioned on
http://www.questarcorporation.com) one may expect the border to be at f/8,
f/5.6 or even f/4.
2010\05\16@012321
by
Russell McMahon
An utterly superb tutorial* on diffraction limits as applied to
camera and other lenses, examples, calculators, hover to see
demonstrators and more.
http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
Extract:
As two examples, the Canon EOS 20D begins to show diffraction at
around f/11, whereas the Canon PowerShot G6 (compact camera)
begins to show its effects at only about f/4.0-5.6. On the
other hand, the
Canon G6 does not require apertures as small as the 20D in order to
achieve the same depth of field (for a given angle of view) due to its
much smaller total sensor size (more on this later).
More extracts from this page at end of this email.
Note that "begins to show" is far from the limit of its useful range.
See web page.
* Hint: "tutorial is a mis-spelling of "primer".
______
1. Admin hat on:
> > ... BTW, regarding the word "existence", I wonder, does ...
It is explicitly against both the letter and spirit of the list rules
to mount explicit, implicit or even vaguely adumbrated "argumentum ad
hominem" attacks on list members. Please refrain from doing so on
list. By all means criticize list members about their spiiling
mistooks and the size of their mother's army boots offlist in private
email. Hint: Don't do this with someone with too many web smarts or
vast technical capability at any geographic remove, no matter how
great.
********* Admin hat off and locked away. ***********
2
>> www.questarcorporation.com/QuestarPDF/QM_100_30003.pdf
>>> Operating range of f/no: 6.0 to 3.5 (less than 14 or 22)
VERY nice toy.
{Quote hidden}>> Those figures are the maximum possible aperture (= minimum
>> aperture number) at varous distances. Smaller apertures can
>> usually be used in practice at any given distance - just not
>> larger ones.
> Yes, but that was not a telescope, that was a microscope; there was no
> need to catch as much light as possible (at least for that price). The
> very reason for the existence of the big apertures must be - better
> resolution, I believe. My point (possibly wrong) was that "diffraction
> could be the major issue at f/14", not to say at f/22.
It is actually a telescopic microscope - ie it is a microscope whose
forte is much greater distances to object than is usually the case.
Questar usually deal with objects at light-years remove but have
lowered their range in this case.
A system with the largest possible aperture as a starting point is,
all else being equal (which it never is), liable to be superior to one
with smaller maximum aperture. A system which does not have constant
aperture across the range - eg f 1:2.8 all the way, almost always
indicates that a compromise has been used between performance and
cost. The "Gold Standard" is constant aperture across zoom range and
this is what you get in most top zoom lenses. If you don't it's
usually because they are 'pushing the envelope" in some other area.
[[I own NO 35mm zoom lenses with constant aperture. The closest I have
is a superb Minolta 17-35mm f2.8-f3.5. This is such a limited range
lens that it is about the only one that Sony decided not to build when
they took over Minolta's camera division. Probably the best lens I
own. ]]
So. I stand by what I said technically, so far. FWIW.
An utterly superb tutorial* on diffraction limits as applied to camera
and other lenses, examples, calculators, hover to see demonstrators
and more.
http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
Hint: "tutorial is a mis-spelling of "primer".
______
>From above tutorial / primer:
Recall that a digital sensor utilizing a bayer array only captures one
primary color at each pixel location, and then interpolates these
colors to produce the final full color image. As a result of the
sensor's anti-aliasing filter (and the Rayleigh criterion above), the
airy disk can have a diameter approaching about 2 pixels before
diffraction begins to have a visual impact (assuming an otherwise
perfect lens, when viewed at 100% onscreen).
As two examples, the Canon EOS 20D begins to show diffraction at
around f/11, whereas the Canon PowerShot G6 (compact camera) begins to
show its effects at only about f/4.0-5.6. On the other hand, the
Canon G6 does not require apertures as small as the 20D in order to
achieve the same depth of field (for a given angle of view) due to its
much smaller total sensor size (more on this later).
Since the size of the airy disk also depends on the wavelength of
light, each of the three primary colors will reach its diffraction
limit at a different aperture. The calculation above assumes light in
the middle of the visible spectrum (~510 nm). Typical digital SLR
cameras can capture light with a wavelength of anywhere from 450 to
680 nm, so at best the airy disk would have a diameter of 80% the size
shown above (for pure blue light).
Another complication is that bayer arrays allocate twice the fraction
of pixels to green as red or blue light. This means that as the
diffraction limit is approached, the first signs will be a loss of
resolution in green and in pixel-level luminance. Blue light requires
the smallest apertures (largest f-stop number) in order to reduce its
resolution due to diffraction.
2010\05\16@084016
by
Olin Lathrop
Marechiare wrote:
> It clearly points out "You shouldn't stop down beyond f/16 due to the
> limiting effects of light diffraction." That's why I persist with my
> point.
That's one lens with a exacting test done in the lab specifically looking
for diffraction effects. Even this test showed little degradation at f/16.
If I remember right, you were claiming problems at f/11. Keep in mind that
diffraction is always there, the question is when it becomes significant
enough to matter. Obviously that is somewhat subjective. Note that this
test skipped every other F stop. The next data point they showed was f/32.
Obviously the diffraction effect at f/22 will be somewhere in between.
Clearly it is possible to measure this in a lab, but I think you'd have a
very hard time spotting the difference between f/16 and f/22 taken with that
lens in real pictures that aren't contrived to show this effect.
Back to Vitaliy's case. He was using f/14. Of course he was using a
different lens. However the original point you objected to, which was that
diffraction effects are unlikely the source of his symptoms, still seems
quite valid.
Also keep in mind the symptoms Vitaliy described. He said at f/14 there was
"noise" on the picture. That's the opposite of what diffraction effects
make a picture look like. Diffraction looks more like a haze. It's a low
frequency effect, whereas Vitaliy was clearly seeing a high frequency
effect.
********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014. Gold level PIC consultants since 2000.
2010\05\16@093646
by
Lee Jones
|
> Say you have a small object (about the size of a postage stamp)
> that you are trying to photograph at high resolution. You can
> get it all in focus using a large aperture setting (say, 14) but
> it comes out sort of blurry/noisy. When you use a small aperture
> setting (say, 4) you can get really sharp details, but the depth
> of field is so narrow, that in 3/4 view you can only get a part
> of the object in focus.
Then something is wrong with your lens. Depth of field is much
greater at large f/stops than at smaller ones (up to a point --
at very small f/stops, say f/64 or f/128, I believe diffraction
effects reduce quality; these f/stops are usually only on view
camera lenses; hmmm, aperture opening on small sensor cameras at
large f/stops, may be small enough for this effect to occur -- I
just don't know).
For a fixed lighting situation, as you increase the f/stop the
shutter speed will decrease to keep constant illumination at the
focal plane. Maybe it's not a lens artifact that you are seeing
but motion blur (camera or object or both) due to a slow shutter
speed when you select a large f/stop.
My recommended procedure for macro photography (cameras using
bellows systems are ignored to keep instructions managable)...
Mount the camera body on a tripod. It's easier if you can mount
the camera to a micro-adjusting platform then mount the platform
to the tripod. This allows you to move the camera & lens fore
and aft without refocusing (which changes magnification).
Put a macro lens on your SLR (film or digital, physics of light
doesn't care). Set desired magnification on lens.
Rough position the object so that it is nearly in focus. Move
camera/lens forwards & backwards until desired focus point is
sharp. If specific magnification is immaterial, use focus ring
on lens plus camera/lens movement to achieve sharp focus.
If object is flat, ensure that object surface is perpendicular
to the lens axis. Remember that your lens' "plane of focus" (*)
may be slightly curved, either concave or convex. Macro lenses
are usually pretty good in this regard.
Optionally, use camera's depth of field preview to ensure that
all that you want sharp is actually sharp.
Use largest f/stop consistent with reasonable shutter speed for
given lighting conditions. If shutter speed goes down too much,
add more light (or pray). Normally, mirror slap may cause some
blurring between 1/30 down to 1/2 (varies by model). Use mirror
lock up function if available. Use a cable release or self-timer.
> Of course, you can move the camera back, but then you don't get
> the high resolution.
A nit pick, but I'd say you would get the same resolution but at
a lower magnification.
Lee
(*) not sure if this is the correct term, I mean the plane formed
from all the sharpest focus points over the angle of coverage
of the object field in front of the lens.
2010\05\16@093830
by
Marechiare
|
|
>> It clearly points out "You shouldn't stop down beyond f/16
>> due to the limiting effects of light diffraction." That's why I
>> persist with my point.
>
> That's one lens with a exacting test done in the lab specifically
> looking for diffraction effects. Even this test showed little
> degradation at f/16.
That's not that little degradation: 200 vs 165
> If I remember right, you were claiming problems at f/11.
It was Vitaliy, the OP, who talked about f/14,you who said that
diffraction should not be a problem at f/14 and me who said that
diffraction could be a problem at f/14.
> Obviously the diffraction effect at f/22 will be somewhere
> in between. Clearly it is possible to measure this in a lab,
> but I think you'd have a very hard time spotting the difference
> between f/16 and f/22 taken with that lens in real pictures
> that aren't contrived to show this effect.
Of course, I got no experience in the area (and I don't plan to get
any), but even I would definitely spot the difference visually between
MTF 200 at f/8 and MTF 150 at f/22. The link was:
http://www.photozone.de/canon-eos/167-canon-ef-100mm-f28-usm-macro-test-report--review?start=1
And for Russell's example "Canon PowerShot G6 (compact camera) begins
to show its effects at only about f/4.0-5.6", the difference would be
even greater. Who knows, perhaps Vitaliy owns exactly PowerShot G6?
> Back to Vitaliy's case. He was using f/14. Of course he was
> using a different lens. However the original point you objected
> to, which was that diffraction effects are unlikely the source
> of his symptoms, still seems quite valid.
>
> Also keep in mind the symptoms Vitaliy described. He said
> at f/14 there was "noise" on the picture. That's the opposite of
> what diffraction effects make a picture look like.
Vitaliy said: "it comes out sort of blurry/noisy", not just "noisy".
2010\05\16@095654
by
Marechiare
> A system with the largest possible aperture as a starting point is,
> all else being equal (which it never is), liable to be superior to one
> with smaller maximum aperture. A system which does not have constant
> aperture across the range - eg f 1:2.8 all the way, almost always
> indicates that a compromise has been used between performance and
> cost. The "Gold Standard" is constant aperture across zoom range and
> this is what you get in most top zoom lenses. If you don't it's
> usually because they are 'pushing the envelope" in some other area.
> [[I own NO 35mm zoom lenses with constant aperture. The closest I have
> is a superb Minolta 17-35mm f2.8-f3.5. This is such a limited range
> lens that it is about the only one that Sony decided not to build when
> they took over Minolta's camera division. Probably the best lens I
> own. ]]
I think, I've got the point. Thanks.
2010\05\16@095914
by
Olin Lathrop
Marechiare wrote:
>> Also keep in mind the symptoms Vitaliy described. He said
>> at f/14 there was "noise" on the picture. That's the opposite of
>> what diffraction effects make a picture look like.
>
> Vitaliy said: "it comes out sort of blurry/noisy", not just "noisy".
Yes, we really need to see Vitaliy's f/14 picture.
********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014. Gold level PIC consultants since 2000.
2010\05\16@161617
by
M.L.
|
On Fri, May 14, 2010 at 6:53 PM, Vitaliy <piclistEraseME.....maksimov.org> wrote:
{Quote hidden}> A question for Russell et al. :)
>
> Say you have a small object (about the size of a postage stamp) that you
> are
> trying to photograph at high resolution. You can get it all in focus using
> a
> large aperture setting (say, 14) but it comes out sort of blurry/noisy.
> When
> you use a small aperture setting (say, 4) you can get really sharp details,
> but the depth of field is so narrow, that in 3/4 view you can only get a
> part of the object in focus.
>
> Of course, you can move the camera back, but then you don't get the high
> resolution.
>
> Short of photographing the front, middle, and back, and stitching them
> together in Photoshop, what are the options?
>
> Thank you in advance.
>
> Vitaliy
>
Use a small aperture and leave the shutter open for a longer period of time.
If the image is junk then it's your camera (since you already said it's on a
tripod with a remote shutter release.)
It is also possible that you have your ISO setting too high. It should be
lower for less noise.
And yes, if you want to send me a RAW file that would help me diagnose your
problem.
--
Martin K.
2010\05\16@163117
by
Richard Prosser
|
|
On 17 May 2010 08:15, M.L. <EraseMEmlkeng.net> wrote:
{Quote hidden}> On Fri, May 14, 2010 at 6:53 PM, Vitaliy <
RemoveMEpiclistEraseMEEraseMEmaksimov.org> wrote:
>
>> A question for Russell et al. :)
>>
>> Say you have a small object (about the size of a postage stamp) that you
>> are
>> trying to photograph at high resolution. You can get it all in focus using
>> a
>> large aperture setting (say, 14) but it comes out sort of blurry/noisy.
>> When
>> you use a small aperture setting (say, 4) you can get really sharp details,
>> but the depth of field is so narrow, that in 3/4 view you can only get a
>> part of the object in focus.
>>
>> Of course, you can move the camera back, but then you don't get the high
>> resolution.
>>
>> Short of photographing the front, middle, and back, and stitching them
>> together in Photoshop, what are the options?
>>
>> Thank you in advance.
>>
>> Vitaliy
>>
>
>
> Use a small aperture and leave the shutter open for a longer period of time.
> If the image is junk then it's your camera (since you already said it's on a
> tripod with a remote shutter release.)
>
> It is also possible that you have your ISO setting too high. It should be
> lower for less noise.
>
> And yes, if you want to send me a RAW file that would help me diagnose your
> problem.
>
> --
> Martin K.
> --
Which gives another possibility to the problem - if the egdes are nice
and sharp, could a high level of (JPEG ?) compression be adding
visible artifacts to the picture? I haven't seen (or don't remember)
any comments about picture format or compression in this thread.
It would be really useful to see an image.
RP
2010\05\16@174834
by
Olin Lathrop
Richard Prosser wrote:
> Which gives another possibility to the problem - if the egdes are nice
> and sharp, could a high level of (JPEG ?) compression be adding
> visible artifacts to the picture?
But that wouldn't change with aperture. While a good thought, it's unlikely
the problem in this case.
> It would be really useful to see an image.
Definitely. Where is Vitaliy? We have heard from him in a couple of days.
********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014. Gold level PIC consultants since 2000.
2010\05\17@144936
by
Vitaliy
|
|
The response is overwhelming (thank you), and this being Monday it will take
me some time to read over the responses and analyze the samples Russell sent
me off-list.
Olin Lathrop wrote:
> Vitaliy wrote:
>> Based on the content of your email I'd say you are the one who's
>> confused, and I fail to understand why. What is the alternative to
>> the F-stop?
>
> The confusion was because you referred to "14" as a larger aperture than
> "4". That means either these are not common F-stop values or you are
> confused, since high F-stop values actually mean a smaller arpeture.
I didn't say it was a "larger aperture", I said it was a "larger aperture
setting" (14 being a larger value than 4). Though I can see now that I could
have said it better.
{Quote hidden}>> It may be strange to you, but it is what it is. I can send you a RAW
>> image if you are eager to check the metadata to confirm the fact.
>
> No, f/14 is unusual, but there is nothing wrong about it. I was trying to
> make sure you really meant this and there wasn't something else going on.
> Like when debugging a PIC program, you look for little things that just
> don't seem right. Sometimes they are right after further investigation.
>
> However, it might be useful to show the two pictures you describe. This
> is
> not to verify the arpeture setting, but to see the nature of the
> distortions
> and noise. These are hard to describe in words, and the true problem may
> be
> easier to diagnose when the symptoms can be carefully examined.
I'll try to upload them when I get a chance. It is not high priority for me
right now, because as I mentioned we solved the problem on the digital side.
Although I would like to know if there is an "optical" solution, going
forward.
{Quote hidden}>> All of your guesses are based on the assumption that my photographer
>> and I are morons. So your suggested solutions below are useless.
>> Thank you for the effort.
>
> Not morons, but unfamiliar with some of the details and physics of
> photography. After all, you did ask, and you demonstrated some confusion
> about arpetures or at least how they are communicated, so I think this is
> a
> justified assumption.
>
> Instead of just dismissing my explanation and suggestions because you
> think
> that I think you're a moron, I'd like to hear at least why specifically
> you
> think my explanation is wrong and therefore the suggestions ineffective.
> So
> far you have provided no facts that refute my guess as to what is going
> on,
> only unwarrented insults.
Olin, I don't know what in my response qualifies as an "insult", but I am
sorry that I was direct/bordering on rude. I guess I was tired and your
"people who actually know what they're talking about" rubbed me the wrong
way.
I mentioned in an earlier post (responding to William "Chops" Westfield)
that the low light/higher sensitivity setting assumptions are incorrect. All
the settings are fixed, the only variable that is changing in response to
the changes in aperture, is the timer setting.
Vitaliy
2010\05\17@230713
by
Lee Jones
>> I'm guessing he's not seeing diffraction effects as much
>> as sensor noise. Diffraction is a rather subtle effect, and
>> unlikely to be a major issue at f/14.
> I'm afraid, diffraction could be the major issue at f/14.
I haven't anyone mention ... diffraction is related to the
absolute size of the aperture (the "stop" formed by the iris)
inside the lens. That aperture is commonly expressed as a
ratio based on focal length. (*)
The absolute aperture size is the same with a 14mm lens at f/14
(e.g. point & shoot camera) or with a 100mm lens at f/100 (e.g.
Digital Rebel XT with common Canon macro lens).
Unless you know the focal length of the lens AND the f/stop, you
can't draw reasonable conclusions about diffraction effects.
Lee
(*) It was found early on (circa late 1800's) that lens behavior
in terms of exposure and depth of field was based on this
relative ratio, not absolute size of aperture.
2010\05\17@233351
by
Lee Jones
Russell wrote:
>> www.questarcorporation.com/QuestarPDF/QM_100_30003.pdf
>>
>> Operating range of f/no: 6.0 to 3.5 (less than 14 or 22)
> Those figures are the maximum possible aperture (= minimum aperture
> number) at varous distances. Smaller apertures can usually be used
> in practice at any given distance - just not larger ones.
This is a mirror lens. I think the aperture is fixed (for a given
focus distance). I know this is so with my mirror lenses -- 8" x
2000mm Schmidt-Cassegrain telescope is f/10 when used as a lens
(for all reasonable focus distances).
Questar appears to have optimized this mirror lens for close up
focusing. As such, the effective focal length changes and given
a fixed mirror size, the f/stop ratio changes. Things get hinky
when you are working at such close focusing distances (related
to the focal length of the lens).
You get f/6 when operating at 33.5cm distance and f/3.5 when at
the closed 15cm distance.
Lee
2010\05\18@003346
by
Russell McMahon
Re achieving larger than usually achievable depth of field:
This page provides another means of achieving your aim.
"Focus stacking":
http://www.equisetites.de/palbot/tools/focus_stacking.html
Some programs free, some not.
The free "CombineZ Movie" aka CZM seems to do almost exactly what you want.
Note also the tutorial on using CZM towards bottom of page.
Lots of other related useful stuff as well.
R
.
_camera
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