I ask this question to all those who have a lens or two that exhibits severe loss of contrast, usually in a circular pattern when the lens is stopped down.
I got prompted on this issue, because I have such a lens, a Rikenon 135mm F2.8 screw mount, and because there was a post a few weeks ago with a complaint that their 645 pentax lenses took poor photos on their K20.
https://www.pentaxforums.com/forums/pentax-dslr-discussion/102680-my-k20d-tak...enses-why.html
The results looked the same as mine, and I assumed, wrongly, that it was sensor reflection off the elements.
When reviewing the thread as it developed, and photos of the adaptor were shown, it was obvious there were shinny black surfaces all around the optical path. The OP used part of an old sock to absorb the light reflecting off these surfaces and posted before and after shots with the same lens.
This got me thinking about my Rikenon 135, so I looked at it, and the retaining ring for the rear element was indeed very shinny black.
I painted it with flat black acrylic craft paint, and the difference is amazing, as shown by the shots below, before and after shots of my "lens calibration wall" where I check exposure consistendy, and also a more real world subject.
While I am pleased that I fixed this lens, the issue was more principle than cost, I hate buying anything that does not work properly, it opens up a bigger question. Is the issue of sensor reflection off the rear element a myth, and the issue really is poorly finished internal lens parts.
What do you think?
One thing I know, I have to go back and edit my lens review, and perhaps upgrade the rating based on what I now know