As a newbie to LF and on a tight budget I have pieced together a kit over the last year(Cambo SC). I acquired by default a Schneider Xenar 135mm f4.7 which has seen better days optically. Indications are that the previous owner taught Ice Skating on the front and rear surfaces.
I have run a preliminary batch of shots using this lens, trying to test the clarity of the image especially some backlighting through trees and river shots with lots of glare.
Can anybody offer a method of testing without putting the lens on an optical bench to ascertain whether to ditch the lens and look for a cleaner alternative?
Phil, If it were me, I would shoot a typical scene and enlarge the negative to the largest size typical print.(your preference) If the print conveys what you want in the terms of sharpness and tonal separation, then I would keep the lens. If not then I would get another. But as in all things, this is a matter of your satisfaction with the result that you produce.
The problem with using an older, possibly suspect lens for your first LF shooting is you have nothing to compare it to. You may use the lens and think it is totally acceptable compared to previous experience with other formats, yet put up against a newer or more pristine older lens it will be lacking in quality.
If you know any other LF shooters in your area, borrow a lens that is of known quality, regardless of its age. This would show you any major defects in your lens.
If the lens does not produce the quality your seek, but has a good consistent shutter, I would purchase another Xenar maybe from Ebay with a gaurantee and keep the old one. You never have enough good shutters. Other lenses in that price range are 135mm Optars and the 127mm Kodak Ektars.
If the lens surfaces are very worn, the most noticable problem you will have is a diffusion effect or flare around strong highlights. I had an Optar like this once and had to return it.
Many older lenses show a bit of a halo around strong highlights anyway due to spherical aberration (it can actually be a nice effect), but it has a somewhat different quality than the effect of diffusion or flare, as the image should still be sharp if the glass is clean, and it should sharpen up as you stop down.
If you find you can't make a sharp image at any aperture, get another lens.
I have an old Ektar that suffered at the hands of an overzealous cleaner. And honestly, I haven't noticed much of a problem. Those lenses can take some serious bashing apparently. Going off of 4x5 polaroids taken with that lens and an Ektar that is very clean, I can't see any difference.
Probably the most important thing is that it works for you.