comparision between Digaron-W 50 mm, Grandagon 65 mm, Biogon 53 mm

[Alkibiades]

This comparison could be interesting for people who looks for a good lens in the rage of 50-65 mm and can not or dont want spend a lot of money for the Digaron-W 50 mm, that is certainly the best lens in this range.
There were always a lot of questions about the grandagon 65 mm that is a very good option.
Biogon 53 mm is a very rare lens, there is no lens that could be compares to it. This lens is made to be used already wide open and not as Super Angulon/ Grandagons that were designed to use at 16-22.

 

[Alkibiades]

First the Rodenstock Digaron HR 4/50 mm.
this lens is even wide open simply perfect.
Made at aperture 4:

 

[Alkibiades]

here the Grandagon-N MC 4,5/65 mm wide open:

 

[Alkibiades]

As expected the center at 65 mm is sharp, the contrast very good but the courners wide open soft and not usable.
So here the same situation at the best working apeture for this lens, aperture 11:

 

[Alkibiades]

at ap. 11 the grandagon is very good.

 

[Alkibiades]

so let see the zeiss biogon 53 mm ( made for Linhof technika 69):

 

[Alkibiades]

So even wide open at aperture 4,5 the Biogon 53 mm have a superior optical quality.
This lens is even single couted, but the contrast in this light situation is also very good, even wide open.
The edges are really sharp!

 

[Alkibiades]

about calibration:
aspecially such high end lenses like the Digarons ( S, W and SW) needs a perfect calibration to deliver they best optical performance.
here a example for a perfect calibrated 50 mm HR and a comparition for a not as well calibrated one, just watch the extrem corners, you will see that the adges become soft, where the well calibrated is perfect sharp. When you move the lens the difference will become even bigger.

 

[JaapD]

Thanks for sharing. The 50mm-4.jpg doesn't look like a high MP image. Can you tell us what the original image size is of which you've made the detail images out?

Thank you!

Cheers,
JaapD.

 

[Alkibiades]

I have done all the pics with Phase one IQ250 with 50 MP.
It has the same pixel density as the 100 MP backs ( differance only in the ship- size)
The whole images are croped, becouse even jpg are too big as a file.
The details are saved at 100 %, but afcourse the are jpg that have lower quality.
Afcourse the best option would be to send raw files but this is not possible here.
But you should see the differences on these details-jpgs.

 

[jng]

about calibration:
aspecially such high end lenses like the Digarons ( S, W and SW) needs a perfect calibration to deliver they best optical performance.
here a example for a perfect calibrated 50 mm HR and a comparition for a not as well calibrated one, just watch the extrem corners, you will see that the adges become soft, where the well calibrated is perfect sharp. When you move the lens the difference will become even bigger.

Thanks for sharing your analysis. By "calibration" are you referring to shimming (in other words, making fine adjustments in the distance between the front and rear lens cells by placing shims between the cells and shutter body)? With the help of @4x5Australian, I've come to understand that proper shimming is critical for addressing field curvature - something I learned as he very patiently navigated us through my purchase of his SK 60XL (thank you, Rod!).

John

 

[Alkibiades]

Thanks for sharing your analysis. By "calibration" are you referring to shimming (in other words, making fine adjustments in the distance between the front and rear lens cells by placing shims between the cells and shutter body)? With the help of @4x5Australian, I've come to understand that proper shimming is critical for addressing field curvature - something I learned as he very patiently navigated us through my purchase of his SK 60XL (thank you, Rod!).

John

John

exact.
The right calibration is extremly important.
better lens needs even better calibration.
60 xl was very known for critical calibration, several copies were not good enough, Schneider had to recalibrate them.

 

[4x5Australian]

exact.
The right calibration is extremly important.
better lens needs even better calibration.
60 xl was very known for critical calibration, several copies were not good enough, Schneider had to recalibrate them.

Just to clarify: The fault is with the third-party Copal 0 shutter being out of specification, not with the lens cells themselves.

A Copal 0 shutter is meant to separate the front and rear cells by a length (i.e., depth) of "20mm +/- 0.025mm", and generally this is the case.

Occasionally, a Copal 0 shutter is made thinner than the specification and the discrepancy is manifested as degraded imaging performance, which hopefully gets detected during the optical performance inspection checks of the assembled lens and shutter by the lens manufacturer. But not always.

The discrepancy is remedied with a shim placed between the shutter and lens cell. I have found shims of 0.1mm or even 0.2mm inserted, which shows that Copal 0 shutters can be far from the proper length specification.

I have also found some other lenses, notably three Schneider 28XL lenses, whose imaging performance was below expectation but lacked shims. In each instance, rotating either the front or rear cell markedly improved the imaging performance and showed that the inter-cell distance provided by the Copal 0 shutter was the culprit. I was able to make the imaging performance of those three 28XL lenses equally excellent. Based on that and subsequent experiences, I have concluded that the instances of poor lens performance reported by users are due, overwhelmingly, to out of spec Copal shutters.

 

[rdeloe]

+1 for what Rod (4x5Australian) wrote!

By all means send your lenses back to the factory for calibration if you have the money to do that, but if you don't it is possible to make dramatic improvements using a simple setup.

I've taken lenses from mediocre to excellent through a step-wise approach: start with the rear cell at all the way tight in the shutter, make a picture of the test chart, loosen by 1/4 turn, make a picture, loosen by another 1/4 turn, make a picture, etc. Repeat until it's obviously gone from bad through good and back to bad. Then compare and choose the best one. To fine tune, start at the best one and then make a set of pictures on either side with finer turns. Once you have the correct spacing, insert a shim. Done. The hardest part is sourcing shims of various thicknesses.

 

[Paul Spinnler]

Who sells shims nowadays? Is this a mail to Rodenstock?

 

[rdeloe]

Who sells shims nowadays? Is this a mail to Rodenstock?

I don't know if anyone sells shims. I keep a stockpile of shim-making materials around from lens disassembly and other projects. I never throw that kind of thing out (and ditto for screws!)

What's hard to replicate is a proper circular shim the correct size and thickness -- which again is an argument for sending your lens to the manufacturer if one doesn't want to mess around with a self-made solution.

 

[jng]

The process that Rod (@4x5Australian) and I used on his->my SK60 XL was as @rdeloe described - iteratively loosening one of the cells (in this case, the front cell as it's more easily accessible), finding the sweet spot, and then calculating the thickness needed based on the thread pitch - 1/4 turn seemed to be optimal, which IIRC works out to 0.12~0.15mm, although I may have slipped a decimal in there somewhere (h/t to @dchew for the [correct] info - I don't have the Copal manual with design specs in front of me).

Finding shims of the appropriate thickness (or any thickness, for that matter) proved to be the biggest challenge in my limited experience, however. I contacted multiple shops on multiple continents, some of which after valiantly searching didn't have any, while others just flatly stated "send the lens back to Schneider, you should leave this to the professionals so they can do it right with their test equipment." To which I say maybe - my main use case is shifting out to the edge of the image circle at distant focus, which I don't know falls within the parameters used by the manufacturers (my ultimate test is in the field). And all these DIY shenanigans assume that the lens isn't decentered or otherwise knocked out of spec.

Anyway, looking into this a bit further, one can get a precision metal shop to cut shims for you but this typically requires a minimum order of 100s with a total cost in the neighborhood of $1000+ USD. Any takers?

My solution was one of serendipity: Rod had seen an SK 135 in Copal mount for sale on eBay for not a lot of $$ and a generous return policy, and for some reason the seller had a picture of it broken down into front and rear lens cells and Copal, showing two shims hanging off one of the cells. @dchew (Dave) was looking for a spare Copal shutter so on a gamble I purchased the lens. When it arrived, one of the shims was missing but as luck would have it, the remaining shim gave a 1/4 turn offset, so I installed it on my lens and shipped the rest to Dave.

Final note(s): while I optimized the lens to offset field curvature, this wound up introducing longitudinal chromatic aberration (purple fringing) at the edge of the image circle. A thinner shim may have been a better compromise but I found that Capture One's purple defringing tool could mostly eliminate the fringing. It's also important to confirm that you can still hit infinity focus after making the adjustment. If I learned nothing else, "fun" with tech cams can be quite the adventure but worth the effort if one is patient and gets a little help from one's friends.

John

 

[buildbot]

Finding shims of the appropriate thickness (or any thickness, for that matter) proved to be the biggest challenge in my limited experience, however. I contacted multiple shops on multiple continents, some of which after valiantly searching didn't have any, while others just flatly stated "send the lens back to Schneider, you should leave this to the professionals so they can do it right with their test equipment." To which I say maybe - my main use case is shifting out to the edge of the image circle at distant focus, which I don't know falls within the parameters used by the manufacturers (my ultimate test is in the field). And all these DIY shenanigans assume that the lens isn't decentered or otherwise knocked out of spec.

Hmm how precise do they need to be? OSHCut has 301 shim stock, hardened , and probably could cut that small... might not be very flat though? OSHCut would be like, 5$ for a run of a few I think. https://www.oshcut.com/capabilities/

 

[buildbot]

Hmm how precise do they need to be? OSHCut has 301 shim stock, hardened (too thick!), and probably could cut that small... might not be very flat though? OSHCut would be like, 5$ for a run of a few I think. https://www.oshcut.com/capabilities/

Okay, 7$ each, 15 setup:

 

[rdeloe]

This kind of thing is a lot easier if you're OK with "janky" solutions.

This is my Mamiya N 43mm f/4.5 L after modifications. I couldn't find a circular shim the right diameter, but I had a piece of brass that was curved and the right thickness. I cut two pieces: one for each side. You can see one of them here. I "temporarily" wrapped the join with electrical tape; it's still there because it works, and I'm all about function rather than pretty.

By the way, this was a fascinating example of how this can all get weird when you're adapting lenses. Bill Rogers (awesome Mamiya tech in Nevada) did the gut job on the innards, and as part of that process he uses the correct Mamiya tools and procedures to confirm that the right shim is in place and that the spacing is perfect. This is the equivalent of "Send it back to Rodenstock". Weirdly, the correct spacing for a Mamiya 7 is completely wrong for a GFX camera. Image quality at the "correct" spacing was horrendous. I had to use the procedure I described above to get to a spacing that worked for GFX. If I was only using this lens on my F-Universalis, the fact that I'd now lost infinity wouldn't be an issue; it's a unit focusing lens that I focus with the F-Universalis. However, I also use this on an adapter I made for hacked Mamiya 7 to GFX. To make this lens usable on that adapter, I had to adjust the helicoid. All my other Mamiya 7 lenses required no adjustment of cell spacing. It's strange, but it works superbly well so I'm fine with the jankiness.