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'[OT] Sigma camera lens repair.. .'
2006\04\08@093749 by Russell McMahon

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An unlikely topic - but who knows the depths of experience present on
the PICList.

Short:    Anyone had any experience in autofocus repair in lenses
and/or know if Sigma parts can be bought.

Longer:

I just bought a used Sigma 28-200mm IF f3.5-?5.6? lens. Works very
nicely indeed, if one ignores the dire problems described below. It's
one generation back from their latest.

It obviously had "issues" at the time I bought it, despite the seller
saying that it had always worked perfectly. The price was low and, as
it came with a Minolta 5000 (film) camera that fits my Minolta lenses,
I decided that the purchase was worth the risk. The lens proved to be
nice enough to be worth buying a new-old one on ebay, but the one I
have is now something of a challenge (and cost enough to be worth a
little effort on principle).

To shorten the story, it sometimes autofocuses OK but often makes bad
grunching noises and doesn't autofocus. I now have the lens outer
layers dismantled down to where I have the autofocus mechanism in
pieces - quite a few layers and parts but not tooooo complex - a
little scary as one inexperienced slipup may doom the lens forever.
(I've already badly bent one set of grey-code encoder wipers which I
didn't know were there until I withdrew the ring they were mounted
under.)(Repairable- hopefully).

Fortunately the lens mechanism proper is a single module which "lives"
inside the outer auto-focusing control shells and I have not had to
dismantle it. The problem is that the large drive track/gear for the
autofocus, which is formed on the inside of the focus control ring, is
nicely stripped and generally abused. For good measure the
housing/bearing  for the drive gear shaft is somewhat broken at one
end, allowing the gear to lift somewhat out of engagement and, no
doubt, hasten the stripping process. (Something may have dropped into
the gear path originally and caused the housing to break as the gear
tried to ride over the obstacle or the lens may have been dropped.

I *think*/***hope*** that I can 'repair' the gear by turning it to a
new position and making a new mounting for the stop/grey-code focus
encoder wipers mounting/... which is attached to it. Bearing housing
can probably be persuaded to think it's OK. (drill/tap/melt/glue/...).
I will also see if parts are available but I strongly suspect that
access to these will be very "closed shop" and I suspect that parts
costs will be unrealistically high.

I'd be interested in hearing from anyone who had delved into such
things or knows of access to parts.


       Russell McMahon


2006\04\08@095108 by Rolf

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Russell McMahon wrote:
> An unlikely topic - but who knows the depths of experience present on
> the PICList.
>
> Short:    Anyone had any experience in autofocus repair in lenses
> and/or know if Sigma parts can be bought.
>
> Longer:
>
> I just bought a used Sigma 28-200mm IF f3.5-?5.6? lens. Works very
> nicely indeed, if one ignores the dire problems described below. It's
> one generation back from their latest.
>
> It obviously had "issues" at the time I bought it, despite the seller
> saying that it had always worked perfectly. The price was low and, as
> it came with a Minolta 5000 (film) camera that fits my Minolta lenses,
> I decided that the purchase was worth the risk. The lens proved to be
> nice enough to be worth buying a new-old one on ebay, but the one I
> have is now something of a challenge (and cost enough to be worth a
> little effort on principle).
>  
[snip]

Two things... contact Sigma and tell them what's broken, you may be
surprised what they will do for a repair.

-- or --

Wait patiently until another broken lens comes up on e-bay, use it for
parts. Perhaps contact local stores for broken lenses that are on hand.
I used to have a very similar lens on my minolta camera a couple of
years ago before I went digital. They are around.

Rolf

2006\04\08@100145 by Mike Harrison

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On Sun, 09 Apr 2006 01:35:29 +1200, you wrote:

>An unlikely topic - but who knows the depths of experience present on
>the PICList.
>
>Short:    Anyone had any experience in autofocus repair in lenses
>and/or know if Sigma parts can be bought.

A while ago I bought a Sigma lens 'as faulty' on ebay, and I was very pleasantly surprised to find
that they were happy to supply parts (in my case a flexi-print), and supplied promptly from a phoned
credit-card order.
This is the sort of thing that makes me more likely to buy products from a company....

2006\04\08@115412 by Russell McMahon

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> I used to have a very similar lens on my minolta camera a couple of
> years ago before I went digital. They are around.

This is for my 7D Minolta digital FWIW.


   RM

2006\04\08@163938 by peter
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If your lens resembles this:

http://www.epinions.com/Sigma_AF_28_200mm_f_3_5_5_6_DL_Aspherical_Hyperzoom_Macro_for_Canon_EOS__Camera_Lenses_787101

then it is likely not worth fixing, except as a hobby/learning process. Getting
parts will be interesting, usually one special orders the parts from the after
market service unit of the manufacturer. Many times this can only be done when
one has a special relationship with said unit (as in, approved service lab, a
status usually achieved after at least one tech takes a course with the
manufacturer).

The hardest part will be to ensure calibration at or near the ends (infinity and
closeup). Full testing of the lens may be required before you waste a film on
testing (and you can't see much in the viewfinder, you have to use a microscope
which is a part of the infinity jig). Do you have an infinity test jig ?

good luck,
Peter



2006\04\10@042655 by Alan B. Pearce

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>I'd be interested in hearing from anyone who had
>delved into such things or knows of access to parts.

If you get in too deep, I'll give you the contact details for my Father, who
lives in Wellington. He made his living repairing cameras. He is retired
now, but will probably still have contacts for spares etc in NZ.

2006\04\10@043849 by Alan B. Pearce

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>The hardest part will be to ensure calibration at or near
>the ends (infinity and closeup). Full testing of the lens
>may be required before you waste a film on testing (and
>you can't see much in the viewfinder, you have to use a
>microscope which is a part of the infinity jig). Do you
>have an infinity test jig ?

My Father has one made by Carl Zeiss. He was always amazed how much
difference there was between infinity set up on that and looking at an
object that was far enough away that one would normally consider it to be
"at infinity", especially with a long telephoto.

2006\04\10@051914 by Russell McMahon

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> >I'd be interested in hearing from anyone who had
>>delved into such things or knows of access to parts.
>
> If you get in too deep, I'll give you the contact details for my
> Father, who lives in Wellington. He made his living repairing
> cameras.
> He is  retired now, but will probably still have contacts for spares
> etc in NZ.

Thanks.
I'll keep that offer in mind!

This is not an economic task by any standard ;-)
But for several reasons I want to make it work.
I wont spend 'forever' on it but if I can get my labour rate
equivalent value over $10/hr (or 5 ? ) and fix it I'll be happy
enough.

I've contacted Sigma locally but so far haven't found anyone who
answers a phone who can tell me anything, or anyone who knows anything
who will answer, nor anyone who will return generic email, nor anyone
whose
personal email address I know who hasn't left the company a year ago.
Maybe tomorrow :-)

Lens problem is clear and very possibly repairable as is, but parts
would be much better. It's built in the area that matters like a "Made
in Japan" toy of 40 years ago. ie adequately to meet the target market
after a fashion but most unlikely to last long enough with any sort of
vigorous treatment. There is a large plastic ring gear on the inner
diameter of the focus ring. This is acted on by a small brass gear
which is on the end of a 15mm odd long axle. The axle runs in a
plastic
tube on the surface of a ring that the focus ring rotates within. The
end of the tunnel where the gear resides has had its roof broken away
when the gear tried to lift radially inwards and succeeded.
Lifting may have been caused by something falling into large gear
track (should be v clean in there) or perhaps from a broken tooth part
starting things off. A person manually over-riding the focus or an
external shock could have started the damage. The specific damage is
listed on the net by lens repairers so this isn't a one off.

As a result of the bearing damage the gear has some positional slop
both circumferentially and
inner-radially. It has chewed out the track on the focus ring at one
end of its travel and has badly compressed and worried the plastic
gear through the rest of its length. On first inspection I thought the
gear was stripped throughout but after very magnified inspection I see
that the gear teeth have largely grown into the space between the
gears making it hard for the metal gear to run nicely. I have largely
cleaned this up - main tool = vvv small jewellers screwdriver used as
a chisel. I can PROBABLY rebuild the missing tooth using epoxy with
some sort of powdered metal filler for 'strength'. I can PROBABLY
repair the broken tunnel-roof/bearing by filing a shaft sized slot in
a metal band (= thick piece of wire?)(copper/stainless/brass/nichrome/
... ? ) and then epoxying this in place
as a bearing. All this will take little time or forever :-). It may
quite well work.

Another approach to the gear damage is to rotate the focus ring gear
by a part turn and
remount the metal fork thingy that is screwed to it. This would need a
new mounting extrusion on the barrel surface at the appropriate point
as the original gets thicker at the right point. This has to be
somewhat right as the fork thingy serves all sorts of tasks :-). Stop
for focus ring, mounts for  4 contact gray-code wipers, drives focus
lever
into lens proper. The end stop is not a trivial application either -
go too far and the encoder fingers die instantly.

I bent one encoder dual-finger vvvvvvvv badly b4 i knew they existed.
it
was remarkably resilient and responded to micro-surgery amazingly
well. Tweezers and same screwdriver blade and heaps of magnification
are main tools.

So, lots of fun. This, of course, in my 'spare' time :-(.

There are some nice new later versions of this on ebay .... :-)

FWIW there are several generations of the Sigma 28-200 zoom. They seem
to have filter ring sizes of 68mm, 72mm, 62mm in order of arrival.
I've got the 72mm. From reviews it seems that some people may be
happier with it optically than the newer version?

This exercise has already taught me things about camera systems which
I (, if not my wife,) feel to be well worth what I paid for the camera
& lens combined. ($NZ95 = ~~ $US60ish). Now, making it work reliably
enough to give me, say, 1 years trouble free service, is of more
account than the $ spent.




       RM

2006\04\10@062113 by Russell McMahon

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> >The hardest part will be to ensure calibration at or near
>>the ends (infinity and closeup). Full testing of the lens
>>may be required before you waste a film on testing (and
>>you can't see much in the viewfinder, you have to use a
>>microscope which is a part of the infinity jig).
>> Do you have an infinity test jig ?

It's for my Minolta 7D DSLR, so wasted film is not a problem. The 7D
has direct to PC download capability (which I haven't tried yet) so
this would make examination of images far quicker when iterating. I
have not needed to touch the lens module proper as it comes out as a
unit, so I *imagine* that "all" that is required is to properly locate
the lens rear the proper distance from the image plane (assuming it is
square thereto). It seems that this will not be an impossible task. If
it is then ...

> My Father has one made by Carl Zeiss.

... I may be making the acquaintance of Alan's father :-)
(Only about 400 miles from here).

Zeiss is good :-).


       RM

2006\04\10@092734 by Robert Young

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> -----Original Message-----
> From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu
> [.....piclist-bouncesKILLspamspam@spam@mit.edu] On Behalf Of Russell McMahon
> Sent: Monday, April 10, 2006 5:21 AM
> To: Microcontroller discussion list - Public.
> Subject: Re: [OT] Sigma camera lens repair.. .
>
>
> > >The hardest part will be to ensure calibration at or near
> >>the ends (infinity and closeup). Full testing of the lens
> >>may be required before you waste a film on testing (and
> >>you can't see much in the viewfinder, you have to use a microscope
> >>which is a part of the infinity jig).  Do you have an infinity test
> >>jig ?
>

You mention this is a DSLR so this trick might not work.  But, for a
film SLR you can make an infinity focus rig from an empty GLASS slide
mount, some frosted scotch-tape and a second camera with a known good
infinity focusing lens (preferrably 50mm or at least something with a
similar diameter to the lens in question).  You will also need a
reversing ring compatible with both sizes of lens.

I may be skipping some detail here (or possibly getting something
ass-backards), I can look it up later.

1) Make a target of the slide mount by carefully scratching an X on the
surface of the glass.  You might want to put the frosted tape on the
opposite side of the glass to give it some visible texture.
2) Tape the slide to the film rails inside the camera.  You will
probably need to remove the camera back and also part of the slide mount
so that the X is centered in front of the lens and in the film plane.  
3) Attach camera and lens in question to tripod, point at difuse light
source (open sky, well lit concrete, etc).  Attach known good camera and
lens to front of lens in question.
4) Focus known good camera to infinity.  Lock both shutters open (B or T
setting).
5) Looking through known good camera, rotate questionable lens until X
comes into sharp focus.  Now questionable lens should be focused at
infinity.


I have never done this with an SLR lens (let alone a DSLR) but I have
used this trick to adjust the infinity focus on a 35mm range finder.
Got the lens focused at infinity, rotated an adjustable ring on the lens
to re-align its marks with the focus mark on the camera body then
adjusted the mirrors in the range finder.  Got lucky and didn't need to
add any shims between the lens and body.  Once focus was ajusted for
infinity, near focus was good.  Checked near focus with tape measure,
pencil pushed into modeling clay (vertical target) and small piece of
frosted glass held to the film rails.  Watched focus on ground glass
with x10 loupe then checked range finder.  Then checked view through
range finder and looked at focus ring marks compared to tape measure.

Rob

2006\04\10@095511 by Alan B. Pearce

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>You mention this is a DSLR so this trick might not
>work.  But, for a film SLR you can make an infinity
>focus rig from an empty GLASS slide mount, some
>frosted scotch-tape and a second camera with a known
>good infinity focusing lens ...

This is essentially how the Zeiss system does it. A suitable target is
projected down the lens under test, and reflected off a piece of film in the
film plane, back out the lens, onto a mirror and out the eyepiece. I think
the eyepiece uses a semi-silvered mirror to direct the image out, as the
projection is done straight down.

2006\04\10@102336 by Russell McMahon

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> You mention this is a DSLR so this trick might not work.  But, for a
> film SLR ...

I have a compatible film SLR so could use that. Thanks for the
suggestion. Knowing something exists is often at least half the battle
:-).



       RM


2006\04\11@115027 by Peter

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On Mon, 10 Apr 2006, Alan B. Pearce wrote:

>> The hardest part will be to ensure calibration at or near
>> the ends (infinity and closeup). Full testing of the lens
>> may be required before you waste a film on testing (and
>> you can't see much in the viewfinder, you have to use a
>> microscope which is a part of the infinity jig). Do you
>> have an infinity test jig ?
>
> My Father has one made by Carl Zeiss. He was always amazed how much
> difference there was between infinity set up on that and looking at an
> object that was far enough away that one would normally consider it to be
> "at infinity", especially with a long telephoto.

One rule for using a telephoto lens on a camera as infinity jig is to
have it at least 1 F number larger than the camera being tested and at
least 5 times the focal distance of the lens being tested. Obviously
this is not realistic for a F/2 200mm lens. The jig would cost more than
the camera being repaired.

An easy way to get a target at infinity is to shoot the stars (Sirius
preferrably) or the moon at night. 384,000 km is far enough for
infinity. Alternately the light on top of a radio tower that is very far
away would work.

The Sigma lens I posted a link to seems to have back focus (focus
tracking) problems even when new (according to a posting by a tester).

Peter

2006\04\11@185852 by Russell McMahon

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> If your lens resembles this:
>
> http://www.epinions.com/Sigma_AF_28_200mm_f_3_5_5_6_DL_Aspherical_Hyperzoom_Macro_for_Canon_EOS__Camera_Lenses_787101
>
> then it is likely not worth fixing, except as a hobby/learning
> process. Getting
> parts will be interesting, usually one special orders the parts from
> the after
> market service unit of the manufacturer. Many times this can only be
> done when
> one has a special relationship with said unit (as in, approved
> service lab, a
> status usually achieved after at least one tech takes a course with
> the
> manufacturer).

The more I know the less I know - as always.
It appears that there has been a whole line of Sigma 28-200mm lenses.
Mine isn't the above one and isn't the latest one and ...

The lens AFTER the above DL is well spoken of here

       http://shutterbug.com/equipmentreviews/lenses/0103sb_sigma/

and variably so elsewhere.

An approximate lineage seems to be

f/3.8-5.6    68?mm filter
f/3.5-5.6    72mm filter
"                    DL Hyperzoom 67mm filter
"                    Compact Hyperzoom 67mm filter
"                    DG ... 62mm filter

It may be that some are not available for all brands of cameras,
although this seems unlikely.
Once they get to "digital" lenses with cameras with 'different crop
factors' then they may decide to build lenses that only suit some
cameras, but at full frame 35mm all should be compatible.


The Sigma agents here were very cooperative once I managed to contact
them.
I can get a complete autofocus outer shell for about $US70 - albeit in
grey wheras mine is black :-(.

Re your later comment on back-focusing problems. Reports on nominally
identical lenses vary vastly. This seems to depend on specific lens,
camera model, specific camera, user experience, user expectations and
more. Having lenses which appear to be the same model but aren't 9as
above) adds to the joy. What I do know is that the lens I bought
focuses as well as anything else I've got on my 7D and produces photos
which are I consider to be very acceptable for a cheap 28-300mm lens.



       RM

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