I've been posting for a while about shooting pano on 35mm loaded into a 220 back for my RB67.
Most medium format cameras can do some version of this trick -- get a couple (now fairly cheap, or almost free if you have a 3D printer) spool adapters to mount a 35mm cassette in place of a 120 spool, cover up any red frame counter windows (if present), optionally adjust frame counter hardware to deal with film thinner than the film+backing paper of 120, optionally add a frame gate to cover the 35mm sprocket holes and/or help hold the film flat, optionally mask the viewfinder for the new frame size/shape...
I've been slowly working my way toward a really practical way of doing this with my RB67. It has about the same frame width as an Xpan, and very similar focal lengths available (90, 65, and 50 are the wide angle lenses, along with a much more costly 37 mm fisheye). I've got a 3D printed frame gate replacement designed for 35mm film, a roll of cine leader film to use with a second cassette, working toward minimizing film waste due to the long strip that gets exposed when loading without backing paper, a 220 roll holder that will handle the full length of a 135-36 without freewheeling -- really, the only thing I'm missing for field reloads at this point is some way to cut the film near the supply cassette to eliminate needing a changing bag or darkroom to unload (and I'm working on figuring that out).
The RB67 is a lot heavier than an Xpan, but literally thousands of dollars less expensive, with replacement bodies, roll holders, viewfinders, and lenses readily available and no electronics to fail unrepairably without warning.
The latest step here is covering the widest of the Xpan's lenses -- there's apparently a (fairly rare, quite expensive) 35 mm lens for the Xpan, fully rectilinear and with even coverage over the 24x70 frame. The widest rectilinear lens for the RB67 is the 50 mm.
However, recently, I acquired this front-mount conversion lens, a 0.46x wide angle converter for 77 mm filter thread. I expected to see significant vignetting and find it useless for the full 6x7 frame, but hoped that would be limited enough to make the lens practical to use on a 24mm high frame. For $40, it was worth the experiment; worst case, I could mount i on my 90 mm and have the equivalent of a 40 mm, and be pretty confident it would cover fully.
Today, however, I had time to mount the auxiliary lens on my 50 mm, and was amazed to find it fully covering the viewfinder, at least, without any visible drop-off or unsharpness (of course, for the latter especially, processed film is the only real test -- working on it). On a 50 mm, this gives an effective focal length of 23 mm -- not "like a 23 mm on 35mm film" but 50 x 0.45 = (rounded) 23 mm on frames up to 6x8! That's equivalent to about 11 mm on the 35mm frame, fully rectilinear! It even looks wide when I'm visualizing the masked frame (don't yet have a viewfinder mask made up); by my calculation, it should be about 106 degrees corner to corner, on a camera setup that can be recreated for well under $1000 (compared to $3500 to $5000 for an Xpan).
The conversion lens is pretty light and fairly thin, and came with a protective pouch and front and rear caps; not bad for forty bucks. One tradeoff is that, probably to design out vignetting, the front ring on the converter is larger than the rear thread, so I can't use my 77 mm filters on this lens, but I'm sure I can pick up inexpensive filters from the same sources where I got the filters I keep with my RB67 and my Kiev 4.
Most medium format cameras can do some version of this trick -- get a couple (now fairly cheap, or almost free if you have a 3D printer) spool adapters to mount a 35mm cassette in place of a 120 spool, cover up any red frame counter windows (if present), optionally adjust frame counter hardware to deal with film thinner than the film+backing paper of 120, optionally add a frame gate to cover the 35mm sprocket holes and/or help hold the film flat, optionally mask the viewfinder for the new frame size/shape...
I've been slowly working my way toward a really practical way of doing this with my RB67. It has about the same frame width as an Xpan, and very similar focal lengths available (90, 65, and 50 are the wide angle lenses, along with a much more costly 37 mm fisheye). I've got a 3D printed frame gate replacement designed for 35mm film, a roll of cine leader film to use with a second cassette, working toward minimizing film waste due to the long strip that gets exposed when loading without backing paper, a 220 roll holder that will handle the full length of a 135-36 without freewheeling -- really, the only thing I'm missing for field reloads at this point is some way to cut the film near the supply cassette to eliminate needing a changing bag or darkroom to unload (and I'm working on figuring that out).
The RB67 is a lot heavier than an Xpan, but literally thousands of dollars less expensive, with replacement bodies, roll holders, viewfinders, and lenses readily available and no electronics to fail unrepairably without warning.
The latest step here is covering the widest of the Xpan's lenses -- there's apparently a (fairly rare, quite expensive) 35 mm lens for the Xpan, fully rectilinear and with even coverage over the 24x70 frame. The widest rectilinear lens for the RB67 is the 50 mm.
However, recently, I acquired this front-mount conversion lens, a 0.46x wide angle converter for 77 mm filter thread. I expected to see significant vignetting and find it useless for the full 6x7 frame, but hoped that would be limited enough to make the lens practical to use on a 24mm high frame. For $40, it was worth the experiment; worst case, I could mount i on my 90 mm and have the equivalent of a 40 mm, and be pretty confident it would cover fully.
Today, however, I had time to mount the auxiliary lens on my 50 mm, and was amazed to find it fully covering the viewfinder, at least, without any visible drop-off or unsharpness (of course, for the latter especially, processed film is the only real test -- working on it). On a 50 mm, this gives an effective focal length of 23 mm -- not "like a 23 mm on 35mm film" but 50 x 0.45 = (rounded) 23 mm on frames up to 6x8! That's equivalent to about 11 mm on the 35mm frame, fully rectilinear! It even looks wide when I'm visualizing the masked frame (don't yet have a viewfinder mask made up); by my calculation, it should be about 106 degrees corner to corner, on a camera setup that can be recreated for well under $1000 (compared to $3500 to $5000 for an Xpan).
The conversion lens is pretty light and fairly thin, and came with a protective pouch and front and rear caps; not bad for forty bucks. One tradeoff is that, probably to design out vignetting, the front ring on the converter is larger than the rear thread, so I can't use my 77 mm filters on this lens, but I'm sure I can pick up inexpensive filters from the same sources where I got the filters I keep with my RB67 and my Kiev 4.