Originally posted by stevewig Lowell, did you notice during any of your testing whether the SMC filter reduced the flare at all? My guess would be that it had no effect.
I tried with and without filter and also with and without a hoya circular polarizer. Filter did not change mush if anything
The rainbow is a behavior which appears when the sun is inside the full frame image circle but outside the DSLR image circle. I could easily see it, and all the other impacts of flare, i.e. loss of contrast and the aperture shape when present, through the viewfinder.
I have also noticed, when shooting at night my super taks are somewhat vunerable to internal reflections from bright lights, although this is also a filter issue. The SMC filters are the best out of pentax, hoya, canon, nikon, kenko and some cheaper brands tested, but do nothing here.
I find once the sun is at your back it all goes away, and using flash (about F11 and the K10D internal flash in manual mode) the images are pretty good as my cat's nose proves.
I have noticed similar loss of contrast on some other M42 lenses especially wider ones when shooting with the sun close to the angle of view. I suspect that these lenses would benefit from an optimum designed tulip lens hood.
I have not noticed this problem with longer lenses, but it is hard for me to make a general statement for my M42 lenses. I have them scattered all over the map from a manufacturer's point of view and even within pentax from an age point of view, with almost the entire range of ages represented.
24mmF2.5 Tameron Adaptall II
28mmF2.5 vivitar
35mmF2 S-M-C Tak
50mmF1.4 super tak (8 element)
55mmF2 SMC Tak
58mmF2 Helios 44
85mmF1.9 Super Tak
105mmF2.8 Vernon Edonar Preset
135mmF2.8 Tele-Lentar
135mmF3.5 S-M-C Tak
200mmF3.5 Tak preset
The only other one so far that I have seen loss of contrast with at all, but no where near his bad is the vivitar 28. Clearly I need to do more testing.