Sigma 50mm lens with adapter producing red spot in middle. Why?

[jungleexplorer]

So I tried out my Sigma 50mm macro lens that fits my Pentax on my a6500 yesterday using this adapter.

Fotodiox Lens Mount Adapter - Pentax K AF Mount (PKAF) DSLR Lens to Sony Alpha E-Mount

All of the pictures turned out with a purplish red area right in the middle. Can someone tell me why?

Here is a picture for you to see what I am talking about. I have bumped the contrast up on the picture to make the purple area more pronounced.

Why are you trapping pigs?

Not me. A friend. But I live in Texas where feral hogs cause an estimated 2 billion dollars a year in crop and farm damage, so people trap them to reduce the population.

Just FYI, feral hogs are non-native invading species and harmful to other native species and driving some to extinction in their native habitat.



--
I am a rubber wall covered with flubber, which is a metastable compound that reacts with greater force then it is impacted with. So be careful what you throw at me. ;-)

 

[jungleexplorer]

Do you usually shoot at f/22? That's a really small aperture, and probably is in diffraction territory. Might be better to use no smaller than f/11.

Because stopping down give a deeper DOF and I was trying to get the whole pig in focus with a macro lens that has an almost flat DOF.

You might want test the lens at different apertures. My guess is sensor reflections are most visible at f/22.

So I did a test today. I set up a white sheet of paper and started at F2.8 and stepped down each shot until I reached F22. I could not reproduce the effect that occurred in every one of the pig pictures.

Any ideas?

 

[Sympa]

Sensor reflectiosn could also be affected by the distance of the lens to the sensor surface (so the distance the lens is focused at). And there may be a factor that a bright section in the image causes the reflection, but it is mostly visible in darker areas in the image. Shooting a half-white half-black scene may give some insight in this.