I've often read that this is so, but wonder if it is actually true, and if so, by how much. Do the optics bend the light rays in such a way that, even when the issue looks to be covered by the lens iris to the eye, light might still be passing through the effected portion of the lens on its way to the film?
I ask because I have a 100mm Wide Field Ektar* with fungus etching** that looks to be completely covered by the f/11 setting, and much more than covered by f/16. I know the best way to find out the possible effects would be to use the lens, but I had back surgery a while ago, and won't be doing much for months. I'm also not very patient, and I am very curious.
* I got the lens with a 4x5 Speed Graphic. The camera came in a Vulcanoid (I love that word) case with some unmentioned odds and ends, including this lens, which I thought was very nice, even after I found the fungal growth. I cleaned it as best I could, then set it in a sunny window for several days. It hasn't grown since.
** And, wow, are there a million conflicting opinions about fungus on lenses: where it comes from ('it was trapped there when the lens was made'; 'it's everywhere and always a threat'), what it 'eats' (coatings, glass, balsam), how to get rid of it, whether you can get rid of it, what effect it has on images.... It would be nice if some lens manufacturer published some actual research. If they have, I'd like to be pointed at it.
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