Interesting technical problem. I don't see a shift in the point of focus but there does seem to be a greater depth of field in the unfiltered image. A plano parallell filter should not do this as you have only added one "neutral" element to the lens. I suspect a professional optician would have to answer this properly. I have a hard time knowing what could lead to it beyond slight vignetting caused by a thick filter mount that somehow reduced the working aperture. However this seems unlikely with a 55mm macro. It seems more likely with a very wide angle lens. If the camera and lens were fully automatic some mischief might occur in the electronics but it shouldn't happen with a manual aperture lens. So I really haven't come up with anything. The last possibility and probably the best would be the weird variables that can creep into tests run outside of laboratories. If you were to chase this I suspect you would wind up doing a lot of tests. Replicating this test to see if the same thing happens, running depth of field tests at a series of apertures, running the test with different filters to observe results, etc.
After staring at this for awhile I think I see higher contrast in the filtered image and lower contrast in the unfiltered. Photoshop could tell you if this is true. However at the end of all this perhaps the best thing is to blame it all on aliens.
No, I don't see a difference, but, I have to admit that I probably don't have as critical an eye as some others. I know I don't trust my eyes over auto focus in most cases.
KEN THIS IS NOT MY THING, BUT I SEE MOSTLY A DIFFERENCE IN THE FILTER/NO FILTER PIC. SHOULD THERE BE A DIFFERENCE IN FOCUS POINT? LOUIS N.
ReplyDeleteInteresting technical problem. I don't see a shift in the point of focus but there does seem to be a greater depth of field in the unfiltered image. A plano parallell filter should not do this as you have only added one "neutral" element to the lens. I suspect a professional optician would have to answer this properly. I have a hard time knowing what could lead to it beyond slight vignetting caused by a thick filter mount that somehow reduced the working aperture. However this seems unlikely with a 55mm macro. It seems more likely with a very wide angle lens. If the camera and lens were fully automatic some mischief might occur in the electronics but it shouldn't happen with a manual aperture lens. So I really haven't come up with anything. The last possibility and probably the best would be the weird variables that can creep into tests run outside of laboratories. If you were to chase this I suspect you would wind up doing a lot of tests. Replicating this test to see if the same thing happens, running depth of field tests at a series of apertures, running the test with different filters to observe results, etc.
ReplyDeleteAfter staring at this for awhile I think I see higher contrast in the filtered image and lower contrast in the unfiltered. Photoshop could tell you if this is true. However at the end of all this perhaps the best thing is to blame it all on aliens.
No, I don't see a difference, but, I have to admit that I probably don't have as critical an eye as some others. I know I don't trust my eyes over auto focus in most cases.
ReplyDelete