I have a Cambo 470 Wide which is not quite sharp at infinity. Given that the Schneider 47XL seems to be quite a good lens and that the one I have seems in good condition, I wonder what the problem is.
Could the focusing helicoid be off? And in this case, does anybody know of a (hopefully easy) way to recalibrate it?
I don't know how to re-calibrate that particular helicoid- but find yourself a piece of ground glass that can be where the film sits, and remove the ground glass and spring back. Then check your focus on that piece of ground glass.Originally Posted by F64
@domaz: thanks, but I think the helicoid might be shy of infinity.
The moon makes an excellent target that's close enough to infinity if you don't have a collimator. The helicoid is almost certainly adjustable, and it's very possible someone played with it or that it was improperly calibrated when installed.
There are other tricks for calibrating a lens to infinity, such as using another camera with known focus as a collimated light source. Place the 2 lenses facing each other, set the known camera to infinity, shine a light through the back with the shutter on 'B', and adjust the other camera until the light source is sharp. Obviously you'll need to find the adjustment mechanism on the Cambo helicoid to do that. It may need shims, or have shims that need to be removed.
@Jim Noel, @Jody_S: thanks. I do have a ground glass. The 2 lens trick seems quite practical.
Light source presumably is not in the focal plane; not even confined to any plane. You need an object precisely in the focal plane; e.g. the ground glass, with some lines scribbled on the ground side.
YOu don't need ground glass for testing. A single sheet of toilet tissue stretched tightly across the film plane is brighter and does an excellent job.
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