Schneider-Kreuznach APO-Digitar 35mm f/5.6 L-88° on GFX

[4x5Australian]

The question could be solved easily by someone presenting the original technical data table and datasheets for the L-88° that presumably were published on its introduction in 2002.

Perhaps someone somewhere has a pdf on an old hard drive or a hard copy in their filing cabinet.

Rod

 

[rdeloe]

Motivated by Rod's suggestion, I dove into the old Plaubel site using the Wayback Machine (Internet Archive) and found links to a Schneider-Kreuznach data sheet for the version of the APO-Digitar 35mm f/5.6 they were selling in 2005. This is the link: https://web.archive.org/web/20050128222728/http://plaubel.com/ Here are JPEG images for posterity.

Based on these images, it's clear that there are some differences in the optical design of the L-88 and the XL-102. For one, it looks like Schneider was feeling very conservative when they specified the image circle, because in this sheet it's 60mm wide open and at f/11, where the XL-102 is 70mm and 90mm, respectively. A 60mm image circle on the L-88 exceptionally conservative; it doesn't even match the formula, where a 36.4mm focal length with an 88 degree angle of view creates a 70mm circle. Empirically, I'm getting excellent results out to just under 70mm.

 

[rdeloe]

And for easy reference, here are the data sheets for the XL-102 (thanks Rod!)

 

[4x5Australian]

Rob has brought the technical datasheet for the 35L-88° back from the dead. It's a real contribution to our understanding of SK lenses and their development. Thank you, Rob.

To recap: The Apo-Digitar 35 L-88° was issued in tandem with the 24 XL-100° at the Photokina show in September 2002 but was replaced only two years later by the 35 XL-102°.

The two-page datasheet reveals that the 35 L-88° and 35 XL-102° lenses have a number of distinct differences.

Optical parameters: Three of the listed optical parameters differ from those for the XL-102° by small but significant amounts.

Bp’ is the pupil magnification (diameter of exit pupil / diameter of entrance pupil)​

S EP is the entrance pupil position (from the front glass vertex)​

S’ AP is the exit pupil position (from the rear glass vertex)​

Those parameters provide definitive evidence that the two lenses have different optical formulas.

Image circle: The datasheet gives the image circle as 60mm yet the MTF graphs are drawn for an image circle diameter of 70mm. The latter agrees with Rob’s report of a 70mm image circle for the L-88° when used with his GFX 100S. In contrast, the 35 XL-102° has an image circle of 90mm.

(That figure of 60mm is also given by the SK technical sheets for the 47 XL and 24 XL, even though the image circle of the 47 XL is clearly much larger; the later technical brochure gives 113mm. The 60mm value seems to be an early standard statement by SK for its wide-angle lenses, related to an expectation (expressed in its literature of that time) that 4x5 film cameras were being replaced by digital sensors of 24 x 36mm, with an image circle of 60mm satisfying the requirement for shift on that format size.)

MTF: The 60 l/mm line in the f/5.7 graph for the L-88° is distinctly higher than that in the same graph for the XL-102°, suggesting that the changes in the XL-102° that enlarged the angle of view and, with it, the image circle, came at the expense of some image quality at f/5.7. In contrast, the MTF of the two lenses at f/8 and f/11 appear to be identical. The trade-off made for a 90mm image circle in the XL-102° was a very positive one.

Still, the 35 L-88 provides excellent image quality for those photographers not requiring the 15mm shifting capability of the later 35 XL-102°, and at a lower price (!).

Rod

 

[rdeloe]

That's a very helpful analysis Rod. Thanks so much for following up.

It can take a while to get to know a lens properly. I'm a long way from being able to say I know this L-88 intimately! However, the more I use it the more pleased I am with its performance. I'm also discovering some interesting characteristics, some of which may be relevant for people using the XL-102.

One of those is the important of the three screws on the rear being tight! Last night I was exploring slight softness on one side of the image at f/5.6. This was puzzling, but I noticed that one of the screws was a bit loose. When I tightened them all, the softness disappears. This happens because the only thing holding the rear lens group inside the housing that has the Copal 0 thread is the pressure of the circular plate and those three screws.

 

[dchew]

This is a wonderful thread. Thank you both.
Dave

 

[rdeloe]

A bit more about the lens for those who are curious about these things. But first a confession: they had two and I bought them both. It's always nice to have a backup.

The shop I bought the lenses from had a lot of other lenses for the Plaubel system. The sticker on mine says it came from Studio Gieske, which is a going concern. If you know these folks, say "hi" for me and tell them their 35mm APO-Digitar lenses are going to have a good second life.

I like buying lenses from working professionals because they're unlikely to keep using a bad lens for paid work. If they're in good condition, which these ones are, that means they earned someone lots of money. The photographers at Studio Gieske took good care of their equipment because the cells in both units are in excellent condition.

This is what one of these looks like, front and back. As I mentioned at the start of the thread, this unit is the product of a partnership among Schneider-Kreuznach, Plaubel and Jenoptik. That's a Schneider-Kreuznach electronic shutter, in a custom arrangement that is screwed to the Plaubel lens board.


The rear lens group twists off easily. The front lens group is a different story. It's in that cavity so deep that it's difficult to remove the lens cap. I couldn't get a hand grip on the lens group to get it off, and had to build a special tool out of some aluminum pipe. There's rubber on the inside of this tube to protect the front of the lens. Tightening the nut provided a good clamping grip. With a quick twist, the front lens group comes loose.



The front and rear lens groups are very tiny. There's a picture earlier in the thread that shows how the rear lens assembly sits loosely inside the housing with the Copal 0 threads, and is held on only by the pressure of the ring around the rear.

On both of the lenses I bought, three Copal 0 shims totalling 0.21mm were included. I only needed one of the 0.09mm shims to get excellent results on my GFX camera. As explained earlier in the thread, the thickness of the cover glass and the close distance of the exit pupil to the sensor appear to be the reason a closer spacing of the lens groups is needed than normal.


The picture on the right shows the solution the three partners devised for the fact that the front lens group is in the cavity so deeply that mounting filters on the front lens group is nearly impossible. There's a set of threads in the board for filters. This is why in the Schneider-Kreuznach Digitar brochure you see a special IIg centre filter with M67 x 0.5 threads; it's for this assembly.


Unless something new turns up, I think this completes the story of the Schneider-Kreuznach APO-Digitar 35mm f/5.6 L-88. On my F-Universalis setup, where I can only shift 8mm anyway, the 70mm image circle it provides is a perfect match. I am looking forward to working it hard during fieldwork that hopefully starts soon (as long as winter gets over itself and makes way for spring!)

 

[buildbot]

A bit more about the lens for those who are curious about these things. But first a confession: they had two and I bought them both. It's always nice to have a backup.

The shop I bought the lenses from had a lot of other lenses for the Plaubel system. The sticker on mine says it came from Studio Gieske, which is a going concern. If you know these folks, say "hi" for me and tell them their 35mm APO-Digitar lenses are going to have a good second life.

I like buying lenses from working professionals because they're unlikely to keep using a bad lens for paid work. If they're in good condition, which these ones are, that means they earned someone lots of money. The photographers at Studio Gieske took good care of their equipment because the cells in both units are in excellent condition.

This is what one of these looks like, front and back. As I mentioned at the start of the thread, this unit is the product of a partnership among Schneider-Kreuznach, Plaubel and Jenoptik. That's a Schneider-Kreuznach electronic shutter, in a custom arrangement that is screwed to the Plaubel lens board.

View attachment 211726
The rear lens group twists off easily. The front lens group is a different story. It's in that cavity so deep that it's difficult to remove the lens cap. I couldn't get a hand grip on the lens group to get it off, and had to build a special tool out of some aluminum pipe. There's rubber on the inside of this tube to protect the front of the lens. Tightening the nut provided a good clamping grip. With a quick twist, the front lens group comes loose.

View attachment 211727

The front and rear lens groups are very tiny. There's a picture earlier in the thread that shows how the rear lens assembly sits loosely inside the housing with the Copal 0 threads, and is held on only by the pressure of the ring around the rear.

On both of the lenses I bought, three Copal 0 shims totalling 0.21mm were included. I only needed one of the 0.09mm shims to get excellent results on my GFX camera. As explained earlier in the thread, the thickness of the cover glass and the close distance of the exit pupil to the sensor appear to be the reason a closer spacing of the lens groups is needed than normal.

View attachment 211728
The picture on the right shows the solution the three partners devised for the fact that the front lens group is in the cavity so deeply that mounting filters on the front lens group is nearly impossible. There's a set of threads in the board for filters. This is why in the Schneider-Kreuznach Digitar brochure you see a special IIg centre filter with M67 x 0.5 threads; it's for this assembly.

View attachment 211729
Unless something new turns up, I think this completes the story of the Schneider-Kreuznach APO-Digitar 35mm f/5.6 L-88. On my F-Universalis setup, where I can only shift 8mm anyway, the 70mm image circle it provides is a perfect match. I am looking forward to working it hard during fieldwork that hopefully starts soon (as long as winter gets over itself and makes way for spring!)

Woah - not to sidetrack this too much, but I wonder if that gaussoptic program exists anywhere. It sounds like it has the full lens designs for all Schneider lenses at the time?!

Love the lens modding! Would you consider selling the shutters if you don't need them? I think they will work with my jenoptik back haha.

 

[rdeloe]

Woah - not to sidetrack this too much, but I wonder if that gaussoptic program exists anywhere. It sounds like it has the full lens designs for all Schneider lenses at the time?!

Love the lens modding! Would you consider selling the shutters if you don't need them? I think they will work with my jenoptik back haha.

I don't know if it still exists, but here's a link to the user's manual: https://web.archive.org/web/2004120...hneider-kreuznach.com/pdf/foto/gaussoptik.pdf
It looks like it ran under Windows.

 

[daz7]

@rdeloe
Did you buy it in a physical shop or online?
Do they have a website?
I would be interested in some Plaubel bits and pieces.

 

[rdeloe]

@rdeloe
Did you buy it in a physical shop or online?
Do they have a website?
I would be interested in some Plaubel bits and pieces.

I bought it from the eBay store of these folks: https://www.photouniversal.de/

 

[corvus]

Last year I was in the photouniversal store. Nice people there. Their ebayshop is called "fotorabatnix". They still had a lot of this type of offer - lenses with Schneider electronic shutter on Plaubel board.
The only thing that comes to my mind is the saying: "The world is a village"

 

[rdeloe]

Last year I was in the photouniversal store. Nice people there. Their ebayshop is called "fotorabatnix". They still had a lot of this type of offer - lenses with Schneider electronic shutter on Plaubel board.
The only thing that comes to my mind is the saying: "The world is a village"

It is a small world, indeed. I must say though that I've never had more trouble buying something than buying from those folks. I had to use a parcel forwarding service with a German address to be able to purchase the lenses.

 

[John Leathwick]

The rear lens group twists off easily. The front lens group is a different story. It's in that cavity so deep that it's difficult to remove the lens cap. I couldn't get a hand grip on the lens group to get it off, and had to build a special tool out of some aluminum pipe. There's rubber on the inside of this tube to protect the front of the lens. Tightening the nut provided a good clamping grip. With a quick twist, the front lens group comes loose.

View attachment 211727

The front and rear lens groups are very tiny. There's a picture earlier in the thread that shows how the rear lens assembly sits loosely inside the housing with the Copal 0 threads, and is held on only by the pressure of the ring around the rear.

On both of the lenses I bought, three Copal 0 shims totalling 0.21mm were included. I only needed one of the 0.09mm shims to get excellent results on my GFX camera. As explained earlier in the thread, the thickness of the cover glass and the close distance of the exit pupil to the sensor appear to be the reason a closer spacing of the lens groups is needed than normal.

View attachment 211728
The picture on the right shows the solution the three partners devised for the fact that the front lens group is in the cavity so deeply that mounting filters on the front lens group is nearly impossible. There's a set of threads in the board for filters. This is why in the Schneider-Kreuznach Digitar brochure you see a special IIg centre filter with M67 x 0.5 threads; it's for this assembly.


Unless something new turns up, I think this completes the story of the Schneider-Kreuznach APO-Digitar 35mm f/5.6 L-88. On my F-Universalis setup, where I can only shift 8mm anyway, the 70mm image circle it provides is a perfect match. I am looking forward to working it hard during fieldwork that hopefully starts soon (as long as winter gets over itself and makes way for spring!)

Truly Rob deLoe, your ingenuity knows no bounds, and this last detail of the extractions and subsequent rebuild takes the cake.

As the French would say - Chapeau!

John L.

 

[rdeloe]

A quick update on the spacing between the cells....

Earlier in the thread I noted that one 0.09mm shim was needed to get optimum performance. I was out shooting yesterday and noticed that at maximum shift, image quality on the right side didn't match the left. I'd determined that 0.09mm was optimum based on an unshifted frame. Revisiting this to compare maximum shift performance, I've now concluded that 0.12mm produces a noticeable improvement.

It's amazing how much difference that slight change makes: 3/100th of a mm is not a lot, but it's enough to produce a significant improvement.

 

[rdeloe]

I'm not in a position to compare the performance of the XL-102 and the L-88 versions, and given how rare the L-88 lenses are, we may never see the results of that test. Nonetheless, based on using the L-88 extensively in the last week, I was curious to know if the lens data sheets suggested that the XL-102 would be a lot better at my maximum shift (which is 8mm). I don't think they do. In fact, I think they suggest the opposite.

For ease of comparison, here are the infinity charts for the two lenses. The red dashed line marks the edge of the GFX image circle on both charts; the blue dashed line on the XL-102 chart marks the 70mm image circle of the L-88 lens; note that Schneider's data sheet says it's a 60mm image circle, but the math says it's a 70mm image circle. Earlier in the thread, Rod explained why Schneider might have used 60mm on the sheets from this time. I'm assuming it's 70mm for this comparison.

One thing I've noticed about my L-88 is that it is surprisingly good at f/5.6. It's extremely sharp in the centre, with low contrast at the edges, but it maintains detail across the frame. I've never read anyone saying they'd use an XL-102 at f/5.6. Compare the 30 lp/mm lines for the two lens, and I think you can see why. The L-88 is noticeably better right across the image circle. Rod noticed this in his comments, suggesting that the price for the bigger image circle of the XL-102 was paid in resolving power. You can see that here.

A similar pattern is evident at f/11, where the 30 lp/mm lines for both radial and tangential are better across the 70mm circle on the L-88. Charts like this obviously don't tell the whole story, but for my situation, they strongly suggest that if I bought an XL-102 thinking I would get better shifted performance within the range I can use on my GFX plus F-Universalis outfit, I would be disappointed.

The last thing that stands out to me is how the XL-102 seems to fall apart out from 70mm to 90mm in the chart. I've seen samples people have shared where image quality at f/11 looks decent with shift right out to the 90mm edge of the image circle, so obviously the charts don't tell the whole story. But they do suggest that performance falloff can be expected between 70mm and 90mm.