I've been fiddling around, fixing a Russian Jupiter-12 lens that wasn't focusing correctly, and I realised I had a way of checking ir. The Jupiter-12 is a Russian-made version of the Contax Biogon, a 35mm lens which, alas, won't fit the modern Voigtlander Bessa cameras which take Leica-screw lenses. What I needed was some way of checking infinity focus, There's a trick of using a camera, with a long lens, as a collimator. An object in the film place will, with the camera lens set to infinity, appear to be at infinity when looked at through the camera lens. So if you look through that camera lens with an SLR, its lens set to infinity, a sharp image proves both lenses are set correctly. When I'd figured that out, it was quick to set up. A broken CD case gave me a fiece of clear plastic I could use as the object, with a few lines scored on the plastic. Open the back on the old Fed-2, set the shutter to B, and use a cable release. And you can see the image go out of focus as you turn the focus ring on the lens. What was wrong? The lens assembly is screwed into a carrier, which the focusing mechanism moves. It had worked loose. (And it was worth cleaning the old, dried, grease off the threads.) Now just to get some photos as a final check...

This is a picture of the camera with the back off, and the test target in place. I've done a little postwork on the photo to emphasise the lines -- they're on the side of the plastic facing the camera, and don't otherwise show up well.

This is a full-size image taken through the lens being tested. Re-sized to be convenient, and a bit of blurring of the outer areas, all saving bandwidth.

The vignetting is in the original, and down to the size of the len's front element.

And now zoomed in on the central area. You're seeing the detail of the marks on the plastic. Note that the light from behind does make a difference. All the zoom is done in computer, cropping rather than resizing.

And this shows the difference when the lens being tested is not focused on infinity. Remember that wide angle lens have great depth of field, you have to look closely to see a difference.

Finally, the same area of the test target, with a different lens on the camera. I don't think I have the 35mm quite right yet, but the different background lighting, and simply being a different lens, may be a factor. Can I ever get the 35mm to give as good a result as this Jupiter-9 85mm?

I shall have to see what the film reveals...

...hmm... interesting...