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'[EE:] Strobing an LED'
2004\07\29@070025 by Jason S

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I'm working on a project that involves strobing a white or RGB LED in short bursts at a fairly low duty cycle.  At the moment, I'm thinking it will be on for 10us, off for 100us-10ms.

Maximum brightness is important in this application, so how much power can I push through the LED under these conditions without damaging it?  It's rated for 30mA max, and 100mA max peak.  Is 100mA a good guideline then?

Of course, I will be driving it off of a PIC, and the PIC's IO is rated for a lot less.  Will it be able to handle a lot more than it's rated current limit for these short pulses?

Thanks,
  Jason

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2004\07\29@074051 by Roland

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The LED will handle the current at 100mA according to it's duty cycle, but
I would'nt rely on the pic to sink it. A small fet will remove all those
problems.
Mostly, I'm wondering on the application, because if it's for a person to
see, you might want to consider the time response of the human eye. A very
short, bright pulse may not even be seen, but a slightly dimmer, longer
pulse will 'appear' brighter. Also, day/night will be a factor too.


At 04:03 AM 29/07/04 -0700, you wrote:
>I'm working on a project that involves strobing a white or RGB LED in
short bursts at a fairly low duty cycle.  At the moment, I'm thinking it
will be on for 10us, off for 100us-10ms.
>
>Maximum brightness is important in this application, so how much power can
I push through the LED under these conditions without damaging it?  It's
rated for 30mA max, and 100mA max peak.  Is 100mA a good guideline then?
>
>Of course, I will be driving it off of a PIC, and the PIC's IO is rated
for a lot less.  Will it be able to handle a lot more than it's rated
current limit for these short pulses?
>
>Thanks,
>   Jason
>
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Regards
Roland Jollivet

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2004\07\29@084115 by Russell McMahon

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>     Maximum brightness is important in this application, so how much power
can I push through the LED under these conditions without damaging it?  It's
rated for 30mA max, and 100mA max peak.  Is 100mA a good guideline then?/>

Data sheet is the only certai guide. Bond wires used to be the limit. Don't
know about latest designs though. You could probably try your own
qualification tests at higher but unless you wanted to put sifgnificant work
into it it would not be a good idea for a commercial product.

LEDs can also be thermally limited. 3.5V say at 100 mA = 350 mW in a small
sealed package. I have seen applications where people heatsunk LEDs and
achieved several times greater current input! Depends how desparate you are.

____

>    Of course, I will be driving it off of a PIC, and the PIC's IO is rated
for a lot less.  Will it be able to handle a lot more than it's rated
current limit for these short pulses?/>

Absolutely not!
It's not so much "being able to handle" as 'refusing to supply".
At say 5V Vdd the LED may need 1 to over 3 volts depending on element
colour. That leaves 4 to 2 volts actual drop at the PIC pin under very heavy
load. You won't get much over 20 MA. Any number of simple driver cicruits
will do what you want. Single FET or bipolar transistors and a few
resistors, or a logic transistor (with no drive resistors needed) or a
driver IC. (eg ULN2803, ULN2003 etc). In ALL cases using a driver you will
need to control LED current, or else).



       RM

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2004\07\29@163603 by William Chops Westfield

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> At 04:03 AM 29/07/04 -0700, you wrote:
> I'm working on a project that involves strobing a white or RGB LED in
> short bursts at a fairly low duty cycle.

I keep seeing comments in the ads for white LED driver how some of them
have higher-current outputs for 'strobe' use, but I don't think I've
ever seen a camera-like device that uses white LEDs as the "strobe."
It's an intriguing idea; lots easier to control than xenon flash lamps,
and MAYBE just possible at todays sensitivity levels and LED
brightnesses.  Is there some seminal app not somewhere that I've
missed, or are they talking about a different kind of 'strobe'?

BillW

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2004\07\29@172828 by Jason S

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As I mentioned in a previous post, I'm using it exactly because it's easier
to control and at much lower and safer voltage than a xenon lamp.

It should be bright enough for my stroboscope under dim lighting conditions,
but I don't think it's bright enough for a camera.  Also, LED manufacturers
seem to want to focus the beam as much as possible so they can inflate the
candlepower rating, and for a camera flash, you want a wide flood beam to
uniformly light the frame.

Jason

From: "William Chops Westfield" <westfwspamspam_OUTMAC.COM>
Sent: Thursday, July 29, 2004 1:18 PM


> It's an intriguing idea; lots easier to control than xenon flash lamps,
> and MAYBE just possible at todays sensitivity levels and LED
> brightnesses.

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2004\07\29@173042 by Jason S

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Does this mean that for a normal LED project where I want 20-30 mA supplied
to the LED, I can connect the LED directly to the PIC without a
current-limiting resistor and the PIC will automatically supply 20-30mA
without blowing the LED or PIC pin?

Jason

From: "Russell McMahon" <KILLspamapptechKILLspamspamPARADISE.NET.NZ>
Sent: Thursday, July 29, 2004 5:31 AM

> Absolutely not!
> It's not so much "being able to handle" as 'refusing to supply".
> At say 5V Vdd the LED may need 1 to over 3 volts depending on element
> colour. That leaves 4 to 2 volts actual drop at the PIC pin under very
heavy
> load. You won't get much over 20 MA. Any number of simple driver cicruits
> will do what you want. Single FET or bipolar transistors and a few
> resistors, or a logic transistor (with no drive resistors needed) or a
> driver IC. (eg ULN2803, ULN2003 etc). In ALL cases using a driver you will
> need to control LED current, or else).

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2004\07\29@192044 by Jinx

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> It should be bright enough for my stroboscope under dim lighting
> conditions, but I don't think it's bright enough for a camera

If *you* can see it, then a camera can too

> Also, LED manufacturers seem to want to focus the beam as
> much as possible so they can inflate the candlepower rating,
> and for a camera flash, you want a wide flood beam to uniformly
> light the frame

But you don't always need the whole frame do you. Not for diagnostics
anyway - although the picture as a whole itself may not look too "flash"
('scuse the pun). If you wanted to look at a certain part of a shaft then
a single LED would probably do, and you could just add more LEDs
to illuminate other parts at the same time when needed

And there's the option of a small add-on xenon if necessary (eg as
found in throwaway cameras, have a look around, they only go in the
bin and can be had for nothing from film processors). I don't know
much about the technical comparisons of film vs digital, but first entry
on Google seems encouraging for a LED strobe

www.techtronics.com/uk/shop/85-0-sensitivity-ccd-digital-camera-camco
rder.html

Quote -

CCD can detect 80-90% of light reaching it. By comparison, only
a few % of light striking a film is recorded

This high sensitivity makes it uniquely suitable for capturing astronomical
images, where light pollution can be effectively filtered out

It also makes digital cameras a better option for low light/night actions

CCD chips come in 1/4", 1/3", 1/2", 2/3"

The bigger the chip, the higher the sensitivity

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2004\07\29@201824 by Jason S

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From: "Jinx" <TakeThisOuTjoecolquittEraseMEspamspam_OUTCLEAR.NET.NZ>
Sent: Thursday, July 29, 2004 4:21 PM


> If *you* can see it, then a camera can too

My eyes have better sensitivity to low light than any consumer film or ccd
on the market.  Under low light, with a digital or film camera, the grain
and contrast both get very poor.  It quickly gets to the point where no
usable information is captured on the film.

> But you don't always need the whole frame do you. Not for diagnostics
> anyway - although the picture as a whole itself may not look too "flash"
> ('scuse the pun). If you wanted to look at a certain part of a shaft then
> a single LED would probably do, and you could just add more LEDs
> to illuminate other parts at the same time when needed

We were talking about using LEDs to replace a xenon bulb in a camera flash.
For this purpose, it has to be bright and uniform enough, and an LED fails
on both counts.

I can't imagine why it would be necessary to use the stroboscope to take
diagnostic pictures of something.  The flash on the camera would do a much
better job of photographing a freeze-frame of the object.  The stroboscope
is intended to let a person see the stop-motion of the object.by firing
repeatedly each time the object is in the same state.

> And there's the option of a small add-on xenon if necessary (eg as
> found in throwaway cameras, have a look around, they only go in the
> bin and can be had for nothing from film processors). I don't know
> much about the technical comparisons of film vs digital, but first entry
> on Google seems encouraging for a LED strobe

A small cheap add-on xenon flash as found in throwaway cameras takes about 5
seconds to charge.  A stroboscope needs a firing rate of a few hundred hertz
at least.  That's why the xenon tube version I build had to be line powered;
a battery powered circuit can't charge the capacitor fast enough.

> CCD can detect 80-90% of light reaching it. By comparison, only
> a few % of light striking a film is recorded

I'd like to see a more reliable source for this than that site.  The most
expensive consumer digital cameras claim to have a sensitivity equivalent to
ISO 400 film.  These days, ISO 400 is the standard speed for film; the only
reason to go slower is if you want a finer grain.  There are fine grain
consumer films ranging to ISO 1600 (FujiColor Press 1600 for example).
Digital can not come close to touching it.

> This high sensitivity makes it uniquely suitable for capturing
astronomical
> images, where light pollution can be effectively filtered out

This is the sort of thing that makes me think the linked page can't be
trusted.  It basically says by using a sensitive CCD, you can filter out the
bright light that overwhelms the starlight and yet the dim light somehow is
still picked up on the film.  If I take a 1500 watt halogen flood lamp
(switched on of course), and put a white LED right in front of the filament
can you tell if the LED is lit very dimly or off?  How does filtering the
light and using a sensitive detector help?

> CCD chips come in 1/4", 1/3", 1/2", 2/3"
> The bigger the chip, the higher the sensitivity

A frame of 35mm film is 24x36mm (about 1.5 square inches).  That's another
reason film has much higher sensitivity.  Consumer cameras also have tiny
CCDs in the small end of that range, especially because the larger the CCD,
the larger the lens needed to provide the same level of zoom.

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2004\07\29@202654 by David VanHorn

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>
>A small cheap add-on xenon flash as found in throwaway cameras takes about 5
>seconds to charge.  A stroboscope needs a firing rate of a few hundred hertz
>at least.  That's why the xenon tube version I build had to be line powered;
>a battery powered circuit can't charge the capacitor fast enough.

Wrong battery.
Eveready still makes the 510V photo batteries.
They aren't cheap, but dead simple, and fast as can be.

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2004\07\29@212544 by Jinx

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First of all, good luck with your project, hope it works out

> If *you* can see it, then a camera can too

> My eyes have better sensitivity to low light than any consumer film
> or ccd on the market. Under low light, with a digital or film camera,
> the grain and contrast both get very poor.  It quickly gets to the
> point where no usable information is captured on the film

That may be true in low light, but a comparison between you and a
camera is irrelevant when a flash is used. There is no way I'd believe
the human eye can react to a microsecond flash as fast as a camera

> We were talking about using LEDs to replace a xenon bulb in a
> camera flash. For this purpose, it has to be bright and uniform
> enough, and an LED fails on both counts

Then doesn't that render the project pointless ? Just asking

> I can't imagine why it would be necessary to use the stroboscope to
> take diagnostic pictures of something.  The flash on the camera would
> do a much better job of photographing a freeze-frame of the object

Flash/strobe - same thing ?

> The stroboscope is intended to let a person see the stop-motion
> of the object.by firing repeatedly each time the object is in the same
> state

Exactly, and that is when it can be used for diagnoses. For example
gear meshing, shaft twisting and so on

> A small cheap add-on xenon flash as found in throwaway cameras
> takes about 5 seconds to charge

That's quite true, I should have made the distinction between a single
flash and a strobe. However, the base voltage is from small cells. If a
high-voltage reservoir were made then the charge time would be
correspondingly shorter. Although if you can get this to work on LEDs
then there is no charging problem

> A stroboscope needs a firing rate of a few hundred hertz at least

Is that strictly true for all cases ? A repetive action, like a motor or
water stream, is largely predictable and a lower flash rate could be
used. Similarly, high-speed oscilloscopes do not have to run at
super-high-speed on constant waveforms as they are able to
gather all the necessary information because of the repetitive nature
of the waveform

> > CCD can detect 80-90% of light reaching it. By comparison, only
> > a few % of light striking a film is recorded
>
> I'd like to see a more reliable source for this than that site

That's something you'd have to verify for yourself. Maybe a
photographer's site like this would be helpful from a practical
POV

http://www.rit.edu/~andpph/text-digital-stroboscopy.html

And just out of interest, EGG's 1/100,000,000th sec photos of atom
bomb blasts (flash not required that day)

http://www.anomalies-unlimited.com/Bomb.html

{Quote hidden}

I'd say that's an extreme example, and would apply to conventional
film as well. I think what they're talking about is that in a frame with
reasonable contrast, like a starfield, you know where light of interest
is in the image (by examining the data) and can focus, so to speak,
attention on that area. AFAIK many investigative telescopes use
digital sensors, and you wouldn't throw that sort of money and effort
around if it didn't work. And they don't stick telescopes on top of
mountains for nothing

> > CCD chips come in 1/4", 1/3", 1/2", 2/3"
> > The bigger the chip, the higher the sensitivity
>
> A frame of 35mm film is 24x36mm (about 1.5 square inches).
>  That's another reason film has much higher sensitivity.  Consumer
> cameras also have tiny CCDs in the small end of that range,
> especially because the larger the CCD, the larger the lens needed
> to provide the same level of zoom

Yes, that's fair enough. You could also compare how much info could
be stored on a piece of 2" analogue magnetic tape to how much RAM
would be required. Obviously film and digital have their own unique
advantages

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2004\07\30@002717 by Jim Tellier

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Jason S wrote:
<snip>

> As far as I know, an electronic flash has a duration under 100uS.  I
realize
> that I'm undershooting it by an order of magnitude, but I thought that
would
> still be enough for the eye's retension, and would give an even better
> stop-motion effect for higher speed objects.
>
It is not at all possible to generalize the duration of "electronic flash":
the
rule of thumb is that, the higher the power discharged into the flash tube,
the
longer the pulse of light will be.   Some professional lighting equipment
actually
produces a high-energy light "pulse" with a duration approaching 1000 mSec.
The
really "LOW" power flash units are the only ones capable of high-speed
pulses, and
those are generally in the order of 100 uSec.
As far as visual retention goes, 100uS doesn't cut it: it's got to be
something
less than about 100Hz, or you see "flicker".   Consider the reason why the
refresh
scan rate on monitors is (ideally) 70 Hz or more.

Jim

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2004\07\30@022331 by Jason S

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From: "Jinx" <RemoveMEjoecolquittspam_OUTspamKILLspamCLEAR.NET.NZ>
Sent: Thursday, July 29, 2004 6:26 PM

> Then doesn't that render the project pointless ? Just asking

The project I'm working on is to build a tool for visual inspection, it has
nothing to do with photography.

My comment about the LED not being bright enough to use for a a camera flash
was in response to a post by William Chops Westfield, who was talking about
using an LED strobe as a camera flash.  It was tangental to the project of
building a stoboscope, and yes, IMO a project of building a camera
flash/strobe out out LEDs is pointless.

> Flash/strobe - same thing ?

Yes, same thing, but a camera xenon flash/strobe is not the same thing as
the flash/strobe I am working on.

> Exactly, and that is when it can be used for diagnoses. For example
> gear meshing, shaft twisting and so on

Right, but I don't think such a tool is useful in photographing the gear
meshing, etc.

> That's quite true, I should have made the distinction between a single
> flash and a strobe. However, the base voltage is from small cells. If a
> high-voltage reservoir were made then the charge time would be
> correspondingly shorter. Although if you can get this to work on LEDs
> then there is no charging problem

It's a totally different charging circuit, I can't simply connect line
voltage to the charging circuit expecting low voltage off batteries.  I
don't think there is any practical way to modify the battery powered flash
circuit.


> Is that strictly true for all cases ? A repetive action, like a motor or
> water stream, is largely predictable and a lower flash rate could be
> used. Similarly, high-speed oscilloscopes do not have to run at
> super-high-speed on constant waveforms as they are able to
> gather all the necessary information because of the repetitive nature
> of the waveform

Of course its not true for all cases, but it's a more versitile instrument
if it can do the higher frequencies.  99% of the time I don't care how much
bandwidth my cablemodem provider provides, I'm only concered with the
latency.  It's that other 1% of the time when I'm downloading a file that
makes me glad the capability is there whenever I need it :)

> http://www.rit.edu/~andpph/text-digital-stroboscopy.html

I don't think there's any way to do that with LEDs and have useful pictures.
One of my cameras (Nikon F801) can automatically fire a flash a programable
number of times to produce those kinds of pictures (of course the camera
doesn't have a built in flash, and the external flashes that can do a decent
job in that kind of application start at around $500 )

>
> And just out of interest, EGG's 1/100,000,000th sec photos of atom
> bomb blasts (flash not required that day)
>
> http://www.anomalies-unlimited.com/Bomb.html

Those are cool pictures (or is hot more accurate?).  Thanks for sharing
them.  Arguably, they did require a flash, and the most powerful flashbulb
ever built :).

> I'd say that's an extreme example, and would apply to conventional
> film as well. I think what they're talking about is that in a frame with
> reasonable contrast, like a starfield, you know where light of interest
> is in the image (by examining the data) and can focus, so to speak,
> attention on that area. AFAIK many investigative telescopes use
> digital sensors, and you wouldn't throw that sort of money and effort
> around if it didn't work. And they don't stick telescopes on top of
> mountains for nothing

Exactly my point.  The stick telescopes on mountains so there's less air
between the telescope and space *and* to get away from sources of light
polution.  If they could simply filter those out with a high quality ccd,
they could put telescopes closer to the city.  My example may have been
extreme, but that seems to be what the site was talking about.

> Yes, that's fair enough. You could also compare how much info could
> be stored on a piece of 2" analogue magnetic tape to how much RAM
> would be required. Obviously film and digital have their own unique
> advantages

Yep.  In the consumer world, digital has a cheap operating cost which is a
pretty big advantage.  Film has a big quality advantage.  That may change
over time, but we're not even close to being there yet.  The
scientific/industrial side is another world.  Sure they use digital sensors
on those expensive telescopes.  You even mention they throw "that sort of
money" at them.  That's just it; sure if you spend that kind of money you'll
get the quality to show for it, but I think very few consumers would spend
$100k+ for a digital camera.

Interestingly, my F801 camera is worth quite a bit more second-hand today
than I paid to buy it brand new 14 years ago.  The digital camera I bought
for $400 in 2002 routinely sells on ebay for under $80 now.  I guarantee my
film cameras will hold their value over the next 2 years while any digital
camera you buy today will plunge in value.  If digital cameras came close to
being as good as film, I doubt this would be the case.

Jason

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2004\07\30@033329 by William Chops Westfield

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On Jul 29, 2004, at 4:21 PM, Jinx wrote:

>> I don't think it's bright enough for a camera
>
> If *you* can see it, then a camera can too
>
And now that video is usually a cmos or ccd sensor rather than a
scanned vidicon tube, you can potentially use a strobed light source
for the video as well.  But perhaps a 1/100 second light pulse 30 times
a second isn't enough of a sparse duty cycle to make it worth while...
(now, on
web cams, if you can sychronize those 10 or so pulses each second with
the electronic shutter, you might have something useful (and epileptic
fit inducing...)

BillW

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2004\07\30@033330 by William Chops Westfield

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On Jul 29, 2004, at 6:26 PM, Jinx wrote:

> There is no way I'd believe
> the human eye can react to a microsecond flash as fast as a camera
>
Most cheap xenon camera flashes are MUCH longer than a microsecond.
IIRC, most are around a millisecond.

>
> Flash/strobe - same thing ?
>
We seem to be using "strobe" to be stroboscope, as in multiple flashes
per image, for stop-motion analysis and such.  Xenon strobes that do
100 flashes per second or more are pretty rare, I think; LEDs would be
able to do much better.  Depending on how fast the phosphors are.
(OTOH, for some applicationsyou might not need phosphors; CCDs being
sensitive to IR and so on...)

There are applications where a xenon flash is TOO bright, and a slower,
dimmer flash would be preferred if it were technically feasible.  Macro
photography comes to mind (and a ring of LEDs is much easier and
cheaper to implement than a ring shaped xenon tube, too.)  Even
portraits might benefit; LEDs are theoretically color-temperature
tunable, too...

BillW

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2004\07\30@051121 by Russell McMahon

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> Interestingly, my F801 camera is worth quite a bit more second-hand today
> than I paid to buy it brand new 14 years ago.  The digital camera I bought
> for $400 in 2002 routinely sells on ebay for under $80 now.  I guarantee
my
> film cameras will hold their value over the next 2 years while any digital
> camera you buy today will plunge in value.  If digital cameras came close
to
> being as good as film, I doubt this would be the case.

My $2500NZ digital now a year old has been superseded twice and the latest
model is $1800NZ.

I have a 25 year old Minolta SRT303B which I could probably sell for it's
new price if i cared to sell it.

Notwithstanding, the best 35mm format digitals now exceed the resolution
performance of 35mm film using industry recognised standards. Dynamic range
of film is still superior but this is under improvement.

Exceeding the resolution of 2 1/4" and 1/4 plate in person portable systems
at less than the cost of a house may be a dream for a year or two yet.



       RM

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2004\07\30@052404 by Jinx

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> Most cheap xenon camera flashes are MUCH longer than a
> microsecond. IIRC, most are around a millisecond

Presumably you mean the $5 U-type from hobby stores

I've no idea how "cheap", this crowd sell a modified bulb with
peak power o/p in less than 2us (186kB)

http://www.lot-oriel.com/pdf_uk/all/light_xe_pulsed.pdf

And solid state LED/laser down to ps

http://www.ibh.co.uk/products/light_sources/nanoled_main.htm

I've got a distant interest in this BTW. A project in the cupboard
requires a sound-triggered flash. I don't think Jason S said what
his actual application is, sorry if I'm muddying the water

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2004\07\30@055550 by William Chops Westfield

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On Jul 30, 2004, at 2:25 AM, Jinx wrote:

>> Most cheap xenon camera flashes are MUCH longer than a
>> microsecond. IIRC, most are around a millisecond
>
> Presumably you mean the $5 U-type from hobby stores

No, it's more the flash electronics than the tube itself.  Remember
that 1/1000 of a second is pretty short as far as typical camera
exposures go; old 35mm cameras would need to operate the shutter at
1/60 s or so just to make sure that the whole piece of film was "open"
during the "very brief" flash.  As far as I know, MOST xenon flash
attachements for cameras have their maximum output with a duration of
about 1ms; many cut the flash pulse shorter for "automatic exposure",
but they are optimized for light output, after all.

Short flashes (containing the same energy) are more difficult,
requiring higher voltages, more expensive components, and more
attention paid to the circuit design.  The effort you need to go to to
get get those sub-microsecond flashes for photographing bullets is
pretty extreme, and other factors enter into your picosecond laser
pulses.

One way to get interesting photographic effects is to take a bunch of
those cheap disposable cameras and rig up a PIC (heh! on topic) to
trigger them in succession, rather than trying to fire the same tube at
a higher rate...  It's a project on my to-do list...

BillW

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2004\07\30@070341 by Jinx

face picon face
> One way to get interesting photographic effects is to take a bunch
> of those cheap disposable cameras and rig up a PIC (heh! on topic)
> to trigger them in succession, rather than trying to fire the same tube
> at a higher rate...  It's a project on my to-do list...
>
> BillW

In another form that's a time-slice camera (you know the one,
stopped Neo in mid-air in The Matrix)

That was a suggestion I meant to make to Jason in the paragraph
in which I mentioned the sampling scopes. I've a similar thing with
solenoids. Instead of trying to quickly charge a big reservoir cap
to dump into the coil, I use 4 in a cycle

BTW, I love a good photo, and looking around found this

http://dave.golfbuddys.com/hvguy/new/HSphotog1.htm

Interesting theory for the last picture

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2004\07\30@180646 by Jason S

flavicon
face
From: "Russell McMahon" <RemoveMEapptechTakeThisOuTspamspamPARADISE.NET.NZ>
Sent: Friday, July 30, 2004 2:01 AM

> Notwithstanding, the best 35mm format digitals now exceed the resolution
> performance of 35mm film using industry recognised standards. Dynamic
range
> of film is still superior but this is under improvement.

This is something that I was trying to avoid bringing up to further
complicate the thread.  Resolution or pixel count has become some magic
number in the digital camera industry that is supposed to tell you how good
a camera is, but in practice has very little meaning; sort of like megahertz
on PCs. My 2 year old digital camera is 2.3 megapixels.  There are a lot of
3-4 megapixel cameras in the $200 area now, and my digital camera gives far
better pictures.  Of course, my pictures look better on screen at 0.7
megapixels where the extra pixels don't matter at all, but they also look
better as a physical print.  I'm referring to the sharpness, color fidelity,
noise, and even apparent grainyness - my cameras prints *look* higher
resolution than a cheap camera with double the resolution.  All the cheap
high res ones do is waste memory space.  I also know someone with a fairly
new and very expensive 4MP camera that makes the prints from mine look like
they came from a child's toy, so in digital cameras, you get what you pay
for. IIRC the Hubble space telescope's highest resolution sensor is sub-2MP,
and it's certainly a much better sensor than the best consumer device
available.

The lens is one of the most important elements, SLR digital cameras solve
that problem at least.  But most rangefinder digital camers I see seem to
have a lens from a throwaway camera.

Jason

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2004\07\30@181724 by Jason S

flavicon
face
> BTW, I love a good photo, and looking around found this
>
> http://dave.golfbuddys.com/hvguy/new/HSphotog1.htm

I've always loved those kinds of pictures.  When I was in high school, I
built a flash trigging device that had a break-beam sensor.  It waited a
variable short time delay after the beam was broken and then fired the
flash.  It worked very well at shooting milk-drop photos.  I should dig up
the pictures some time and scan them.  I never did come up with any other
kinds of pictures I could take with it.  The ones that capture a bullet use
a sound trigged sensor.  In Canada, it would be very impractical to get the
equipment and find the labspace to capture bullet freeze-frames.

Jason

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2004\07\30@183800 by Olin Lathrop

face picon face
Jason S wrote:
> I've always loved those kinds of pictures.  When I was in high
> school, I built a flash trigging device that had a break-beam sensor.
> It waited a variable short time delay after the beam was broken and
> then fired the flash.  It worked very well at shooting milk-drop
> photos.  I should dig up the pictures some time and scan them.

I did the same thing in high school except using a microphone trigger.  I
set the milk pan on the microphone.  I'll have to see if I can find some of
those pictures and scan them too.


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'[EE:] Strobing an LED'
2004\08\10@104152 by Spehro Pefhany
picon face
At 01:18 PM 7/29/2004 -0700, you wrote:
>>At 04:03 AM 29/07/04 -0700, you wrote:
>>I'm working on a project that involves strobing a white or RGB LED in
>>short bursts at a fairly low duty cycle.
>
>I keep seeing comments in the ads for white LED driver how some of them
>have higher-current outputs for 'strobe' use, but I don't think I've
>ever seen a camera-like device that uses white LEDs as the "strobe."
>It's an intriguing idea; lots easier to control than xenon flash lamps,
>and MAYBE just possible at todays sensitivity levels and LED
>brightnesses.  Is there some seminal app not somewhere that I've
>missed, or are they talking about a different kind of 'strobe'?

The "flash" use LEDs seem to have a very long on-time compared to
xenon discharge tubes (hundreds of milliseconds).

I've built a stroboscope using a small array (5) of super bright LEDs,
pulsed at high current, and it works quite nicely.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
EraseMEspeffspamspamspamBeGoneinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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