Remounting lens in Copal

[Focusrite]

What I have done, which is a little bit ghetto as they say, is to measure the length of the entire lens in the original shutter. If you can put it into the new shutter and match the measurement it should be good. I've done this with a dial gauge indicator which measures to 0.01 mm. With very small measurements you can more or less read half way between the markings for better precision but it's technically outside of the tolerance of the gauge. There are more expensive gauges with higher precision.

Ideally you need a calibrated surface plate to put the lens on for the measurements. I don't have one but managed to get some good readings using a 30mm thick sheet of melamine. The dial gauge goes on a heavy stand and you put the original lens between the gauge and the surface plate, zero the dial gauge, replace the shutter, put it back under the gauge and check the difference. You should move the lens around and take measurements at various locations. If everything is set up well the dial gauge reading should not fluctuate as you move the lens around. It is quite awkward resting the gauge plunger on the edge of the lens barrel so I rested a glass lens filter on top as a reference surface to take readings off. The actual height of it doesn't matter because you are just looking for any difference.

With a proper surface plate and gauge stand you can move the gauge around relative to the lens but I think moving the lens is more accurate and less prone to error. A test indicator instead of a plunger style indictor may be even more accurate and easier to take the measurements from the actual lens barrel, however using the filter as a reference surface isn't bad as it averages out any imperfections that could be in the metal barrel.

I was reshuttering a lens from a SINAR DB mount hence my calibers weren't big enough to take the measurement. Doing it the way I have described also avoids errors from not keeping the calibers or micrometer perpendicular to the object you are measuring.

I've also done what rdeloe suggests with another lens I have, on my Cambo with the IQ4-150. Using live view and a distant object to focus on and taking some frames to compare at 100%. I reshuttered a SINAR 55 mm digital lens to Copal and wanted to check whether the spacing was effecting performance (was great on the Leaf Credo 60, could start to see limitations on the IQ4). The measurement with the gauge is a good starting point though.

All of this depends on the lens being in spec in the original mount so results could vary.

This does look like a solid method for keeping the lens calibration consistent between different shutters (and definitely the method I would prefer!); or at the very least a good benchmark/baseline to start at before further optical tests and tweaking to see if further improvements might be obtained.

My question would be whether it matters about where the aperture is placed in between the front and rear cells and whether that makes any difference with optical performance? I unfortunately know very little about optical design; and although I assume it wouldn't make any measurable difference I do realise that in this business distances in the microns can have significant impact.

Some people shim the rear lens group, others have stated that preferentially the front should be shimmed in accordance to the manufacturer's recommendation, and I wonder what the practical difference between the two options would be: either to not mess with the manufacturer's stated flange focal distance, the precise placement of the aperture/shutter in between the front and rear cells, or some other obvious reason I'm ignorant of.

Maybe one day when I get some suitable gear I'll just reverse the Copal shutter on a lens and see if it makes a noticeable difference to the lens' behaviour.

 

[Ben730]

I regularly switch from Copal to Compur to Schneider E-Shutter to Copal Press. I also used to have Rollei and Sinar electric shutters.
I do the shutter changes when I buy a used lens or to do job-specific work. For example, if I need to take several pictures without touching the camera or if I need a special bokeh.

I would be happy to share my experiences with you when I change a lens shutter and calibrate the lens:

Measuring doesn't help much. In German they say: "Wer misst, misst Mist." This is a play on words.
It means: He who measures, measures crap.
I have already bought lenses that were completely wrongly calibrated.
This gives you an incorrect initial value. In addition, accurate measurement is very difficult.
We are talking about 0.02 mm here.

Buy first some shim rings (0.02 mm, 0.05 mm, 0.1 mm, 0.2 mm).
If you don't know where to get them, try MISUMI (https://uk.misumi-ec.com).
They ship worldwide. The costs are minimal.
The registration process is a bit time-consuming due to the risk of importing weapons etc.
You have to make sure that you are not building weapons.

First, screw the lens elements into the shutter without the shim ring.
Try, test, look.
The best way to do this is to connect the camera to the computer and look with 100% view.
To roughly estimate how many washers you need, you can unscrew the front element of the lens a little.
A quarter turn already makes a difference.
In the image center, the differences are minimal. I therefore recommend testing at infinity in a corner with maximum shift.
The attached screenshot shows a 100 % section of three images with the 90 mm HR Digaron SW.
Sorry, today was a rainy windy day in Lucerne, Switzerland.
They are shifted 25 mm up and simultaneously 20 mm to the right. (That's a lot!)
The first one is optimally adjusted. In the second and third, I unscrewed the front element by 1/4 in each case.
At the same time, you can't see any difference in the center of the image.
Try, test, look, compare.

My preferred shutter is the latest Copal (at the bottom left of the picture, Copal - No. 0).
It has seven rounded aperture blades. The older Copal 0 has only five blades.
The Schneider E-Shutter has five non-rounded ones. This results in a clear pentagon. This can look cool but can also be annoying.
The old Compur shutters are still easy to repair and last a very long time.
They have very round apertures, with countless blades, but are prone to internal reflections as the blades are not completely dark matte.

The plastic ring at the bottom of the picture is mounted on top of an unused Copal. For lenses with a large front element, it must be removed, otherwise the lens cannot be screwed all the way onto the shutter. You can simply click it out with a flat screwdriver.

So, that's everything so far, I hope I haven't forgotten anything. The most important thing is to test and see, it's not witchcraft, it's possible for almost anyone.

Regards,
Ben

 

[diggles]

The plastic ring at the bottom of the picture is mounted on top of an unused Copal. For lenses with a large front element, it must be removed, otherwise the lens cannot be screwed all the way onto the shutter. You can simply click it out with a flat screwdriver.

Thank you Ben! This information in your post is fantastic and the part I quoted explains why I was not able to get my lens sharp outside of the center. I didn't even notice the ring that was keeping the front element from screwing all the way onto the shutter. When the lens came back from being calibrated at Greiner, this ring was in the box.



When they first saw the lens they commented immediately that it was not set up properly. I'd bet this ring installed on the COPAL-NO.0 mount is what they were seeing when they said that.

 

[rdeloe]

To the excellent information here provided by Ben and others, I can add a couple point in no particular order.

My Compur 0 shutter has plastic rings like the ones in Warren's picture that prevent some cells going all the way down. I ran into this when remounting my APO-Digitar 35mm L-88 cells in a Compur 0 shutter. The ring can be removed, which allowed those cells to go all the way down to the front mounting surface.

Ben is right about measuring. I expect that the manufacturers had tools that allowed them to check whether the distance between the mounting surfaces was within spec (20mm +/- 0.025mm for Copal 0). If the best you can do with your own tools is what you see in this picture, don't bother. I measured 10 times and got 10 different measurements. They were all close, but being out by 0.03mm is easily enough to affect image quality.



It's a pain, but some shutters and housings are on the long side of the specification, and some on the short side. I have two Compur 0 shutters (most recent black housing) that are identical, except that one works with a set of APO-Digitar 47mm cells I was trying, and one does not. The only way to find out if a set of cells will work may be to try. Rod Sainty @4x5Australian has mentioned a few times on this forum that in his experience people who have "bad" lenses may just have the wrong shutter; I think that's true.

Fun fact by the way: the housing you see above is from a Componon 135mm enlarger lens. It's Copal 0 thread on both sides. As long as the front cell is no more than 42mm in diameter in the part that sits within the "bowl", they will work. My APO-Symmar 100/5.6 cells fit fine in this housing. The APO-Digitar 47mm f/5.6 Multicoating cells also fit because the front cell has a straight section that is ~42mm before it flares out. They're nice housings because they are all metal and have 19-bladed apertures. The one in the picture is 60 years old and works fine.

I've found that longer focal lengths are much easier to move from shutter to shutter than wide lenses. Don't start a wide angle lens rehousing without a supply of shims. To get best results with the APO-Digitar 47mm cells, I had to find just the right combination of 0.03mm shims. A piece of ordinary paper is about 0.1mm thick, so you can imagine how delicate 0.03mm shims are. They damage very easily and have to be handled very carefully.

Sometimes you can't get good results with a shutter or housing because it is on the long side of the specification. If the cells need to be closer together and there are no shims to remove, you might be out of luck. This happened to me with one wide symmetrical lens I purchased. It likely worked fine on other cameras, but the cover glass on GFX sensors is so thick that the edges and corners of the image are a mess with the "correct" cell spacing. The APO-Digitar 35mm cells I use now and some APO-Digitar 47mm cells I tried yesterday require closer than correct spacing if used with GFX cameras. If you're in that situation and your shutter is long, you only have two choices: (1) try a different shutter and hope it's shorter, or (2) if you're desperate, you can lightly sand the rear mounting surface to allow the rear cell to come a bit closer. This is a desperation move because it's a permanent modification. I had to sand the rear mounting surface of the Componon 135mm housing you see in the picture above to give me the room to adjust the APO-Digitar 47mm cells, but that housing cost me $7 USD plus shipping so I wasn't concerned about permanently modifying it. This worked.

One additional complication with moving cells as close together as I had to for my GFX setup is that the shutter may no longer work. The blades of the Compur 0 shutter that I use with my APO-Digitar 35mm cells catch on the part of the rear cell that projects into the shutter. The aperture blades clear easily, but the Compur 0 shutter has to be locked open. That's not a problem for me because I'm not using the shutter with that lens.

 

[Reginald Fluggelding]

This does look like a solid method for keeping the lens calibration consistent between different shutters (and definitely the method I would prefer!); or at the very least a good benchmark/baseline to start at before further optical tests and tweaking to see if further improvements might be obtained.

My question would be whether it matters about where the aperture is placed in between the front and rear cells and whether that makes any difference with optical performance? I unfortunately know very little about optical design; and although I assume it wouldn't make any measurable difference I do realise that in this business distances in the microns can have significant impact.

Some people shim the rear lens group, others have stated that preferentially the front should be shimmed in accordance to the manufacturer's recommendation, and I wonder what the practical difference between the two options would be: either to not mess with the manufacturer's stated flange focal distance, the precise placement of the aperture/shutter in between the front and rear cells, or some other obvious reason I'm ignorant of.

Maybe one day when I get some suitable gear I'll just reverse the Copal shutter on a lens and see if it makes a noticeable difference to the lens' behaviour.

That's a good point. I've only done a few different lenses and the shims were always on the front of the shutter, so the aperture is going to be closer to the rear element on average. My theory is that the shutters tend to be on the short side, intentionally. You can add shims to get correct spacing but never make the shutter shorter. With some knowledge of machining and turning I know it's not particularly difficult to get something in spec. I would hypothesise given production methods, materials and mechanical construction that it's more likely that lenses have less precision. In both cases a lens or shutter can also be out of spec because of mechanical damage.

And like I said and then Ben370 alluded to "Wer misst, misst Mist." My way is just a starting point to compare two different mounts and try and match them. If the lens was not well calibrated in the original shutter then matching the spacing won't make it any better. I was reshuttering lenses taken from SINAR DB (which is just an aperture mount). On that basis I trust that they were well calibrated, I know they tested them. There is a lot of talk about shutters being out of spec but I highly doubt SINAR would have produced and sold units that were out of spec. I've had a few of them and they had shims.

 

[Reginald Fluggelding]

To the excellent information here provided by Ben and others, I can add a couple point in no particular order.

My Compur 0 shutter has plastic rings like the ones in Warren's picture that prevent some cells going all the way down. I ran into this when remounting my APO-Digitar 35mm L-88 cells in a Compur 0 shutter. The ring can be removed, which allowed those cells to go all the way down to the front mounting surface.

Ben is right about measuring. I expect that the manufacturers had tools that allowed them to check whether the distance between the mounting surfaces was within spec (20mm +/- 0.025mm for Copal 0). If the best you can do with your own tools is what you see in this picture, don't bother. I measured 10 times and got 10 different measurements. They were all close, but being out by 0.03mm is easily enough to affect image quality.

View attachment 212324

It's a pain, but some shutters and housings are on the long side of the specification, and some on the short side. I have two Compur 0 shutters (most recent black housing) that are identical, except that one works with a set of APO-Digitar 47mm cells I was trying, and one does not. The only way to find out if a set of cells will work may be to try. Rod Sainty @4x5Australian has mentioned a few times on this forum that in his experience people who have "bad" lenses may just have the wrong shutter; I think that's true.

Fun fact by the way: the housing you see above is from a Componon 135mm enlarger lens. It's Copal 0 thread on both sides. As long as the front cell is no more than 42mm in diameter in the part that sits within the "bowl", they will work. My APO-Symmar 100/5.6 cells fit fine in this housing. The APO-Digitar 47mm f/5.6 Multicoating cells also fit because the front cell has a straight section that is ~42mm before it flares out. They're nice housings because they are all metal and have 19-bladed apertures. The one in the picture is 60 years old and works fine.

I've found that longer focal lengths are much easier to move from shutter to shutter than wide lenses. Don't start a wide angle lens rehousing without a supply of shims. To get best results with the APO-Digitar 47mm cells, I had to find just the right combination of 0.03mm shims. A piece of ordinary paper is about 0.1mm thick, so you can imagine how delicate 0.03mm shims are. They damage very easily and have to be handled very carefully.

Sometimes you can't get good results with a shutter or housing because it is on the long side of the specification. If the cells need to be closer together and there are no shims to remove, you might be out of luck. This happened to me with one wide symmetrical lens I purchased. It likely worked fine on other cameras, but the cover glass on GFX sensors is so thick that the edges and corners of the image are a mess with the "correct" cell spacing. The APO-Digitar 35mm cells I use now and some APO-Digitar 47mm cells I tried yesterday require closer than correct spacing if used with GFX cameras. If you're in that situation and your shutter is long, you only have two choices: (1) try a different shutter and hope it's shorter, or (2) if you're desperate, you can lightly sand the rear mounting surface to allow the rear cell to come a bit closer. This is a desperation move because it's a permanent modification. I had to sand the rear mounting surface of the Componon 135mm housing you see in the picture above to give me the room to adjust the APO-Digitar 47mm cells, but that housing cost me $7 USD plus shipping so I wasn't concerned about permanently modifying it. This worked.

One additional complication with moving cells as close together as I had to for my GFX setup is that the shutter may no longer work. The blades of the Compur 0 shutter that I use with my APO-Digitar 35mm cells catch on the part of the rear cell that projects into the shutter. The aperture blades clear easily, but the Compur 0 shutter has to be locked open. That's not a problem for me because I'm not using the shutter with that lens.

using a dial gauge/test indicator like I have explained is a lot more accurate than calipers. You'll easily get outside of the caliper tolerance just by not having them fully perpendicular to the shutter and reference surface. My decent Mitutoyo callipers only read to 0.02 mm anyway and that's probably with +- 0.01 tolerance. You can also achieve higher precision just by the function of the dial gauge fluctuating as you move reading positions. If the indictor doesn't fluctuate as you move the object you are measuring you know things are well set up.

Ben730 procedure (which I have used too) is really the best test in the end. It just takes some patience and fiddling. I did this with my SINARON 55 digital (which is really a 55 Grandagon, maybe with some optimisation, better coating, who knows). I came to the conclusion it was as good as I could get it to start: stronger on mid to close range with the image circle opened up more, not perfect but with a overall character that trumps it's foibles.

 

[rdeloe]

using a dial gauge/test indicator like I have explained is a lot more accurate than calipers. You'll easily get outside of the caliper tolerance just by not having them fully perpendicular to the shutter and reference surface. My decent Mitutoyo callipers only read to 0.02 mm anyway and that's probably with +- 0.01 tolerance. You can also achieve higher precision just by the function of the dial gauge fluctuating as you move reading positions. If the indictor doesn't fluctuate as you move the object you are measuring you know things are well set up.

For sure, but my point was it doesn't matter. I suppose if you had a box of shutters and wanted to find the one that had the shortest length you could measure them all with a dial gauge. I don't do this a lot (moving cells into new housings), so an empirical approach works (insert the cells and see how it does). It's quickly obvious whether a shutter or housing is too long.

Ben730 procedure (which I have used too) is really the best test in the end. It just takes some patience and fiddling. I did this with my SINARON 55 digital (which is really a 55 Grandagon, maybe with some optimisation, better coating, who knows). I came to the conclusion it was as good as I could get it to start: stronger on mid to close range with the image circle opened up more, not perfect but with a overall character that trumps it's foibles.

Much patience, and much fiddling! With a fairly simple setup it's not difficult to find the best possible spacing. One just has to be patient.

 

[Reginald Fluggelding]

For sure, but my point was it doesn't matter. I suppose if you had a box of shutters and wanted to find the one that had the shortest length you could measure them all with a dial gauge. I don't do this a lot (moving cells into new housings), so an empirical approach works (insert the cells and see how it does). It's quickly obvious whether a shutter or housing is too long.

Agree. It's really only in the case that you have an already perfectly setup lens in one shutter and want it to match in another shutter that you'd do what I suggest. I also think if you had access to a proper test bench with a collimator it might be a more scientific way of adjusting the spacing than using live view. I would assume that's how the lens makers did it …

 

[Niddiot]

I regularly switch from Copal to Compur to Schneider E-Shutter to Copal Press. I also used to have Rollei and Sinar electric shutters.
I do the shutter changes when I buy a used lens or to do job-specific work. For example, if I need to take several pictures without touching the camera or if I need a special bokeh.

I would be happy to share my experiences with you when I change a lens shutter and calibrate the lens:

Measuring doesn't help much. In German they say: "Wer misst, misst Mist." This is a play on words.
It means: He who measures, measures crap.
I have already bought lenses that were completely wrongly calibrated.
This gives you an incorrect initial value. In addition, accurate measurement is very difficult.
We are talking about 0.02 mm here.

Buy first some shim rings (0.02 mm, 0.05 mm, 0.1 mm, 0.2 mm).
If you don't know where to get them, try MISUMI (https://uk.misumi-ec.com).
They ship worldwide. The costs are minimal.
The registration process is a bit time-consuming due to the risk of importing weapons etc.
You have to make sure that you are not building weapons.

First, screw the lens elements into the shutter without the shim ring.
Try, test, look.
The best way to do this is to connect the camera to the computer and look with 100% view.
To roughly estimate how many washers you need, you can unscrew the front element of the lens a little.
A quarter turn already makes a difference.
In the image center, the differences are minimal. I therefore recommend testing at infinity in a corner with maximum shift.
The attached screenshot shows a 100 % section of three images with the 90 mm HR Digaron SW.
Sorry, today was a rainy windy day in Lucerne, Switzerland.
They are shifted 25 mm up and simultaneously 20 mm to the right. (That's a lot!)
The first one is optimally adjusted. In the second and third, I unscrewed the front element by 1/4 in each case.
At the same time, you can't see any difference in the center of the image.
Try, test, look, compare.

My preferred shutter is the latest Copal (at the bottom left of the picture, Copal - No. 0).
It has seven rounded aperture blades. The older Copal 0 has only five blades.
The Schneider E-Shutter has five non-rounded ones. This results in a clear pentagon. This can look cool but can also be annoying.
The old Compur shutters are still easy to repair and last a very long time.
They have very round apertures, with countless blades, but are prone to internal reflections as the blades are not completely dark matte.

The plastic ring at the bottom of the picture is mounted on top of an unused Copal. For lenses with a large front element, it must be removed, otherwise the lens cannot be screwed all the way onto the shutter. You can simply click it out with a flat screwdriver.

So, that's everything so far, I hope I haven't forgotten anything. The most important thing is to test and see, it's not witchcraft, it's possible for almost anyone.

Regards,
Ben

Really useful - could you tell me what shim size you buy ? Would 35mm ID, 45mm OD be right ? Thanks

 

[Ben730]

Really useful - could you tell me what shim size you buy ? Would 35mm ID, 45mm OD be right ? Thanks

MISUMI Teile-Nr.: CIMRSF-D35-V30-T0.1
Hersteller: MISUMI
Produktbezeichnung: CALLAR

MISUMI Teile-Nr.: CIMRS30-35-0.02
Hersteller: MISUMI
Produktbezeichnung: SHIMS

 

[cunim]

After reading all this, I feel so incompetent. All you handy people, respect!!! My wife changes the light bulbs at our house because I wreck the threads. Time to use an expert.

I have two lenses going to Greiner today (the 120 macro and a 70 HR). After putting the Copal 0 in the macro I cannot get really crisp focus even on center. Adjusting the front element outwards makes it worse so the shutter spacing may be too thick. The 70 HR is still in its Rollei shutter.

There will be two options for element optimization. Greiner will do whatever he does and I hope that will be enough. @diggles seems happy with it so hope I will be as well. If Greiner feels he is not getting the best out of these lenses, Rodenstock have equipment which will do the spacing based on MTF measurements. Expensive but sure. Hoping to avoid that but nice to know it is there.

 

[diggles]

After reading all this, I feel so incompetent. All you handy people, respect!!! My wife changes the light bulbs at our house because I wreck the threads. Time to use an expert.

I have two lenses going to Greiner today (the 120 macro and a 70 HR). After putting the Copal 0 in the macro I cannot get really crisp focus even on center. Adjusting the front element outwards makes it worse so the shutter spacing may be too thick. The 70 HR is still in its Rollei shutter.

There will be two options for element optimization. Greiner will do whatever he does and I hope that will be enough. @diggles seems happy with it so hope I will be as well. If Greiner feels he is not getting the best out of these lenses, Rodenstock have equipment which will do the spacing based on MTF measurements. Expensive but sure. Hoping to avoid that but nice to know it is there.

After getting the lens back from Greiner it can handle the max movements of the Rm3di, 30mm camera fall and 15mm shift, which equals a 120mm image circle. Before sending the lens to Greiner it could only handle a 70mm image circle.

Looking forward to finding out how it works out!

 

[rdeloe]

I think that one thing you may get from Greiner or Rodenstock is what I think of as "true best".

The people who adjust these lenses all the time should have a good understanding of what the very best that is possible looks like. People who do "one off" adjustments for specific lenses can never be sure if the best they're able to achieve is the best that can be achieved with that lens model. Last night, and again this morning, I've been tweaking and adjusting a lens. I can compare it to other lenses of similar focal length, and I can compare it to itself with different adjustments. But what I can't do is compare it to the results of a dozen previous adjustments of the same lens.

In other words, while the lens I've (hopefully) finished adjusting is as good as I can get it, I don't know if it's as good as it can be. Hopefully -- for the money this will cost you -- Greiner or Rodenstock can give you the very best that is possible.

 

[Ben730]

The next hurdle after the correct calibration is the aperture scale.
It's interesting that no questions have arisen about this yet.
The scales are not transferable between different lenses! Each lens has its own scale.
F 5.6 of the Rodenstock HRSW 90mm/5.6 is wider than F5.6 of a Rodenstock HR 23/5.6.
They have different scales.

Here too, measuring is not exact, or rather complex.
How do you compare the aperture of a pentagon with that of a rounded heptagon?
skgrimes.com has the necessary information and can engrave your aperture scales.

 

[cunim]

The next hurdle after the correct calibration is the aperture scale.

Good point. In my case, I am starting with Copal shutters so I will have approximate apertures. That’s good enough to know what to expect in terms of DOF and diffraction. If I had no aperture control of my own, your Grimes suggestion would be the way to go. They can both supply the iris and calibrate it to the lens.

 

[rdeloe]

The Compur 0 shutters I'm using clearly have a way of controlling the size of the maximum aperture because the shutters were configured for the focal length of the lenses they contained (in my case, both were 100mm lenses). There's lots more room for larger apertures in the aperture mechanisms, but the larger apertures are locked out on these shutters. This is only a problem if you're putting a longer focal length in a shutter that was locked down to the maximum aperture of a shorter focal length. In my case, I put 35mm cells in a shutter locked to the apertures needed for 100mm, so the only concern was figuring out where f/5.6 was.

The aperture markings are printed on the housing on my Compur 0 shutters, unlike some of the older Copal shutters where the aperture scale was on a thin metal plate that was screwed onto the housing. I could have had Grimes engrave a nice scale that I plopped on top, but my concern is function rather than form, so I used a hand written label to mark f/5.6 and smaller for the 35/5.6 lens I was mounting.

You can get fancy and determine the actual aperture optically; the procedure is documented in forum posts here and there. I use a rough and ready approach. Set up the camera, set the aperture larger than needed, and close it down until the exposure changes. I'll assume that's the widest aperture and go from there. My concern is the range that defines acceptable image quality for my purposes. I'm less fussed about whether the setting I marked f/8 is exactly f/8. As a final test, I'll compare against another lens that has a scale set up by the manufacturer. If the same aperture setting in the same position with the same focal length on the same scene gives me the same shutter speed, I'm happy.

 

[rdeloe]

A frequent complaint I read when people are adapting lenses is that the lens is bad because it has "tilted elements", which seems to be a generic stand-in for all manner of ills (most of which are not actually tilted elements). What people don't realize is how an extremely tiny alignment or spacing error can make a big difference.

This is my rough-and-ready indoor test setup. These are very high resolution Siemen's Stars printed on good quality matte 8.5" x 11" paper. Nothing about this is perfect, but it works well. The idea is I focus on the centre star, using the ones immediately on the left and right to define the edges of the unshifted frame. The other stars are far enough apart to test various amounts of shift room.


I was finishing up my APO-Symmar 100/5.6 this morning. My simple procedure is to get to the best overall shifted image quality at f/5.6. I would never shoot it at f/5.6, but if it's good at f/5.6, it's going to be terrific where I use it.

Here's an example that illustrates the challenge. This is the APO-Symmar on that wall in the above picture. The columns are the left-most star and the right-most star. This takes 20mm of shift -- which is the maximum I'd likely use (although 25mm is still fine with this lens). With 0.15mm of shim under the front cell, I could get a very good left side and an OK right side at f/5.6. With 0.12mm of shim, left gets worse and right gets better. I don't have shims to split the difference, which would be ideal. At f/8, both sides are fine, and if I shifted this lens 20mm I'd use f/9.5 or f/11.


I started out with no shims, and the left looked horrendous. If I didn't know better, I would have said the lens had "tilted elements".

 

[Ben730]

May I ask what kind of camera you use for these tests?

 

[dchew]

I don't remember if this was discussed in another thread or not, but Copal 0 shutters have an 0.5mm thread pitch. It's easy to calculate the shim thickness required once you figure out how many degrees of rotation you need for the best image. The formula is just 0.5mm x fraction of full rotation. Here is an example:

 

[rdeloe]

May I ask what kind of camera you use for these tests?

I use the camera I'm using the lens on. Currently I use a Fuji GFX 100S. This creates a special issue that seems to be unique to me, which is that the thick cover glass of the GFX cameras must be taken into account. There's a point at which it's not an issue; empirically and very roughly, I'd say lenses wider than 50mm require adjustment specifically for GFX. The 35mm APO-Digitar is a clear example. The cells needed to be closer than would otherwise be the case.