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Author Topic: Re-shimming when replacing (Copal) shutter?  (Read 1569 times)
torger
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« on: May 02, 2013, 06:19:44 AM »
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As far as I understand when you buy a Schneider Digitar or Rodenstock Digaron lens with a Copal shutter they are shimmed to match the specific shutter it's mounted on. That is, the thickness of the Copal shutter varies slightly between copies so to get the proper amount of spacing between the front and rear lens elements to get a really sharp lens you need to shim.

So what happens if your Copal shutter brakes and you need to replace it? If you buy a new Copal shutter separately, is it possible to shim it by yourself (if so how), or do you send the lens with shutter somewhere and get it shimmed?

For the pancake cameras you'd logically send to Alpa/Arca/Cambo, but for us view camera users we are kind of used to mounting our own lenses, at least to the board. I don't think Linhof is providing any lens shimming service, don't know for sure though...
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buckshot
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« Reply #1 on: May 02, 2013, 08:03:40 AM »
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All copal 0 shutters are the same 'thickness' for this purpose. The shimming is performed by a circular metal shim (similar to a washer, in some insane thickness - e.g. 0.001mm) if needed. So, if for some reason at the QC stage the lens needs shimming, i.e. the front and rear groups need moving further apart, then a shim will be inserted (usually behind the front group).

In all my time I have only seen one shimmed lens 'from the factory' - a Schneider 72mm if I remember correctly. I've replaced shutters on lenses many, many times - with absolutely no observable adverse affect.

N.B. This sort of shimming is usually done by Schneider or Rodenstock in-house. The sort of shimming that Alpa and Cambo do when you send a lens to them to be mounted relates to getting the lens to focus at infinity once installed on the helical and mount. This is usually done by removing a few screws on the helical, focussing the lens at infinity (on a test bench, shooting tethered or whatever), setting the ∞ point and retightening the screws. Thomas has a good summary here.
« Last Edit: May 02, 2013, 09:19:47 AM by buckshot » Logged
torger
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« Reply #2 on: May 02, 2013, 11:08:03 AM »
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Thanks for the very informative reply!
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theguywitha645d
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« Reply #3 on: May 02, 2013, 12:23:37 PM »
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I have replaced shutter as well over my career. Never seen any change in performance. The Copal shutters should have universal spacing--not a difficult task to machine for a modern shutter.
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torger
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« Reply #4 on: May 02, 2013, 12:55:05 PM »
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According to this: http://www.alpa.ch/dms/glossary/repair-and-service/copal-0-1-manual/copal_0.pdf the distance tolerance of a copal 0 shutter is +/-25 microns which I assumed to be pretty bad in a digital world. But perhaps the precision is better in practice. I don't know how old that manual is, precision could be better today too.
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RomanN.
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« Reply #5 on: May 03, 2013, 02:53:50 PM »
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Reshimming cost at Rodenstock and Schneider are something about 100 euro, I would always do it for lenses like extremly wide angle 23-28 mm digaron S or Digaron W. The differences could be very big at these lenses. I reshime some longer lenses for myself having the comparision to original reshimmig lens. You need some experiance with that, sometimes good live view can help, always use the shim rigs fot the front element only, never for the rear. For some analoge lenses is reshimming also needeed like Super Angulon XL 120,115, Apo grandagon 110, 120,
the difference on film between original reshimming lens and simply changed shutter can be also very big, you see it in  bad contrast and sharpness in center at open aperture, and not really sharp corners at working apertures.
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ErikKaffehr
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« Reply #6 on: May 04, 2013, 02:00:50 AM »
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Hi,

25 microns would give a CoF of 4.5 microns at f/5.6, I'm not sure that would be visible on 6 micron pitch sensors. Tolerances may add up, however, tolerance in shutter, lens mount, sliding back and sensor.

Best regards
Erik

According to this: http://www.alpa.ch/dms/glossary/repair-and-service/copal-0-1-manual/copal_0.pdf the distance tolerance of a copal 0 shutter is +/-25 microns which I assumed to be pretty bad in a digital world. But perhaps the precision is better in practice. I don't know how old that manual is, precision could be better today too.
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henrikfoto
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« Reply #7 on: May 04, 2013, 03:05:00 AM »
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When the tollerance in the shimming is so critical, how can these lenses be handled without
changing them slightly? There is nothing stopping them from moving slightly in the shutter.
just the strength it is turned with will affect the distance between the elements slightly.
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neilwatson
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« Reply #8 on: May 04, 2013, 09:34:07 PM »
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I once tried taking a series of close focused pictures and between each picture unscrewing the front lens assembly a couple degrees each time.   The corner sharpness for closs focus got better.  But the Pictures at infinity got worse. 
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EricWHiss
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« Reply #9 on: May 04, 2013, 10:09:27 PM »
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I've always planned to do some tests where I set up the camera carefully with the digital back and use a test chart and something like Imatest to check how much or if any differences can be found in the performance by just unscrewing the front or rear a little bit.  I wonder how Schneider and Rodenstock do this anyhow?   

Many of the lenses in the past were convertible - meaning you could remove the rear elements and get a different focal length typically longer so I wonder how much really the spacing matters?  I mean if its that critical, even just the differences in what we all decide is "tight" in turning the front and rear groups into the shutter would make a difference.   But I've never really noticed anything different.
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« Reply #10 on: May 11, 2013, 10:53:06 PM »
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I once read something on schneiders website that warned of moving lenses from shutters other than the original. They said each lens specifically shimmed for the exact shutter and that there were slight differences from shutter to shutter. I have seen lenses of the same model and focal length side by side with shims of slightly different thickness.

I've also heard many people who say that swap their shutters and don't notice the difference.

It's possible that that LF lenses would be more forgiving as they are used at smaller apertures.

The fact that one could call the fitting process for helical mounted lens to a technical camera shimming has nothing to do with using shims to optimize the spacing of lens elements to a shutter.

If there is a difference from shutter to shutter, two shutters might randomly match. So consequences of crude shutter swapping might be non existent in some cases.

In the end your mileage might very, and if it works for you than do it.

I do think that if one ever has to sell a lens that he or she knows is not in its original shutter, than he or she is morally bound to share this information with the new buyer in case of the possibility of quality degradation. One should should add who and how the swap was preformed. I personally would want to know if:

(A) you know that the lens was reoptimized on an optical bench for the new shutter
(B) if the new shutter was precisely matched to the old one by measuring the original shutter and with micrometer accuracy and reproducing the distances on the new shutter (via reshimming if necessary)
(C) The lens elements were simply unscrewed from one mount or shutter and crudely transferred to another without regarding to minute differences between the too.

Perhaps lenses mounted with method C are still good. If one has actually used and tested a lens after it has been transferred then that could and should be mentioned.


All copal 0 shutters are the same 'thickness' for this purpose. The shimming is performed by a circular metal shim (similar to a washer, in some insane thickness - e.g. 0.001mm) if needed. So, if for some reason at the QC stage the lens needs shimming, i.e. the front and rear groups need moving further apart, then a shim will be inserted (usually behind the front group).

In all my time I have only seen one shimmed lens 'from the factory' - a Schneider 72mm if I remember correctly. I've replaced shutters on lenses many, many times - with absolutely no observable adverse affect.

N.B. This sort of shimming is usually done by Schneider or Rodenstock in-house. The sort of shimming that Alpa and Cambo do when you send a lens to them to be mounted relates to getting the lens to focus at infinity once installed on the helical and mount. This is usually done by removing a few screws on the helical, focussing the lens at infinity (on a test bench, shooting tethered or whatever), setting the ∞ point and retightening the screws. Thomas has a good summary here.
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EricWHiss
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« Reply #11 on: May 11, 2013, 11:30:06 PM »
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I've got more than 10 schneider lenses in shutters.  I don't think I've seen one with a shim.  Has anyone?

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« Reply #12 on: May 12, 2013, 12:33:07 AM »
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Look again. You have to unscrew the lens from the shutter to see them. Careful most shims are very thin and easy to loose.

I'd say more than half of the Rodenstock, Schneider, Nikon and Sinar lenses that I have ever seen are shimmed. I'm looking at a 120mm Apo Digitar Macro right now and it has a shim on the front cell.

I've got more than 10 schneider lenses in shutters.  I don't think I've seen one with a shim.  Has anyone?


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EricWHiss
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« Reply #13 on: May 12, 2013, 12:52:02 PM »
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That's interesting but my experience is different.  The only schneider optic I have that seems to have a shim is an old betavaron zoom enlarger lens and it has a shim under the front element.

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torger
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« Reply #14 on: May 13, 2013, 12:47:21 AM »
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Could it be that Copal has improved their manufacturing precision, ie that older lenses have shims but newer don't need it?
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Paul2660
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« Reply #15 on: May 13, 2013, 07:52:24 AM »
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It's my understanding, from talking to Schneider in NY, that each lens, has to be collimated with the shutter.  This is a very involved process and involves adjustment of the lens elements with the shutter installed to make sure the lens will focus at infinity.  I don't know if this involves shimming the actual shutter or another process. 

I reached out to Schnieder when the issue of Copal no longer manufacturing their shutters came up.  I was considering purchase of a spare.  I thought that a company like Precision Camera works in IL could just replace the shutter for me.  After taking to them I realize they were concerned about the  collimation of the shutter to the lens and felt that if the original shutter could not be repaired, then I would have to send that lens back to Schneider or Rodenstock to have the shutter replaced to assure a good focus. 

I realized there is more involved in the process than I realized.  I also don't know if Alpa, Arca and Cambo do this when they attach their specific mounts or if they take the lens from Schneider or Rodenstock already collimated and install it. 

Paul Caldwell
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Paul Caldwell
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EricWHiss
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« Reply #16 on: May 13, 2013, 11:24:29 AM »
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It might be that older designs were more tolerant, or it may be that a select few lenses need to be carefully set because of design, or it maybe that a few applications have little tolerance.  Certainly many lenses were made to be convertible by removing or replacing either group.  In most cameras there is enough travel to adjust infinity settings so I'm really not buying that as a reason for set-up only in the factory or with shims.  Shims only add space anyhow. 

I've got my Imatest set up now and when I get to my LF lenses, I'm going to test this out purely out of curiosity.  I'll unscrew one element a little and see how performance changes if any on some of these.
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studio347
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« Reply #17 on: May 13, 2013, 08:43:43 PM »
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It's a very interesting subject. I have 2 recent schneider digitar lens which has a shim each. I might want to do a test with the lens with the shim and without the shim ... at my typical shooting setting which is a still life set at about f11 or f16. I remember that I saw 3 black shims in a Rodenstock lens...
I think we need someone who have deep understanding in lens design.
For me, I need a very careful test to see... if there is any differences...
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