Hello, big story below for anyone interested but the TLDR is “are colour casts a significant problem when using the Schneider 58mm XL lens on a CCD digital back?”
Full detail:
The past year and a half I've been working on a homemade technical camera to use for exteriors architectural photography, just as a hobby user not a professional. I initially built the camera around 6x7 film using an RB67 back (and designed tolerances accordingly) and have had a lot of successful shots with that unit, mostly with a Nikkor 65/4. Over the past 9mo I've been shifting to tighter tolerances with more CNC and less 3d printing, and bought a P45+ at a good price to get away from the cost and hassle of film, especially with plane travel. I've been loving the files out of that back and while it's a bit clunky to be composing with a ground glass and loupe on a digital back I like the workflow.
In May I took a prototype to Taiwan, bringing a Schneider 47mm (non XL) as well as two Bronica ETRS lenses I'd rehoused into Copal 0 shutters - a 75mm and a 150mm. My experience was the 47mm was plenty sharp for the phase one when stopped down but suffered badly from colour casts and I didn't do a good job of shooting LCC frames, so I "lost" a lot of shots to serious colour casts that are hard to correct.. However I was pleasantly surprised by the image circle, sharpness and lack of casts on the 75mm, which I put down to the difference in FFD and angle of incidence of the rays.
Looking to avoid casts but still not wanting to bother with LCC shots; on a more recent trip to Japan I brought a rehoused 50mm/f2.8 Bronica lens which is a fairly significant retrofocal design (~76mm FFD) - I thought I was pretty clever as the lens is sharp and does not exhibit any noticeable colour cast even with a lot of rise, but having now got the shots on my macbook for some closer inspection I can see the image circle for this lens was very deceptive – it can happily do 20mm of rise without blacking out, but the sharpness suffers badly when doing more than about 12.5mm, which wasn’t obvious on the janky P45+ screen… I think stopping down to f16 would have saved some, but then diffraction is becoming noticeable across the frame so it’s not an overall win.
So now I’m back to the drawing board on what lens I should use as my “wide” with this system (where I’m quite happy with something in that focal length range and can stitch a bit if I want wider). The obvious (and free) one is to just get more disciplined with LCC shots with the 47mm but given the traditional design of that lens and incredibly short FFD I feel like it’s just got to be about worse case possible for angle of rays meaning religiously doing LCCs when there is basically any rise which is annoying. The common suggestion on this forum is a digitar lens or similar, but frankly they just don’t have the image circle for the kind of shots I want to do, and they cost a bomb.. so I’ve been thinking about others and have a 58mm XL available locally for a decent price which got me thinking:
1. Probably just wide enough for my needs – basically a standard lens but I like that for a lot of shots and then can shoot a decently bigger/wider stitched frame if needed.
2. Retrofocus design for bigger image circle should be better behaved for colour casts? (not as retrofocus as the cast-immune 50mm Bronica though)
3. Image circle way exceeds my needs so I should be mostly using just the middle portion and get corner to corner sharpness (although image circle is quoted at f22 where I'm likely to do most work at 8-11, so good to have a lot to spare in the numbers)
4. Can serve dual purpose when I put on the 6x7 back, whereas the 47mm will run out with the amount of rise my body can do.
But probably unsurprisingly I can’t find any good data on whether that design will actually be a noticeable improvement on casts – If I’m still going to need to shoot LCCs basically all the time I’ll save my money and stick to the 47mm, but if the XL lens seems like it will be a better performer on the digital back I’ll take the leap. Does anyone have experience using that lens with a digital back? (I appreciate this may be more of a memory than recent user experience 😊)
