UV Filters on Mamiya 7 Lenses: Testing for Parallel Surfaces
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This is a tale of two filters and why I feel it is important to get high quality UV filters.
When lenses come into the shop with a UV/Sky filter installed I check them as a matter of course on an auto collimator and give a report to the client if they are out of spec. Ideally, each side of the filter would be parallel to each other but 2-3 minutes of angle would be a reasonable margin of error.
The Mamiya 7 80mm lens has a B+W 58ES 010 UV filter installed. The Mamiya 7 50mm lens has a no name, Made in Korea Sklylight (1A) filter.
The second photo show the image from the B+W filter and although it surprisingly shows the surfaces around 12 minutes out of parallel, the image of each star target is sharp. Normally, I see B+W filters at very close to zero angle out of parallel.
The third photo shows the no name filter and it is quite terrible. While it is only around six minutes out of parallel, the star images are not sharp and not good overall. This tells me that the surfaces of the filter are not finished well. No question that I would reject this filter.
Of course, the big question is whether these imperfections would affect image quality. In most cases probably not. But, if you are going for maximum critical sharpness, I would not be overwhelmed with either of these filters although if I had to choose, the B+W filter would be better than the no name filter that I tested here.
