[IsaacSteiner]

Hey,

I have a Pentax-M 40mm F2.8 lens, and at the back of the lens, near the mount, that area of glass has this purple/blue ring around the outside of glass? But it's inside the lens. I went to trade the lens in for something else at Henry's, but they wouldn't trade it because of this little mark or stain.

I attached a photo, so you can see what I'm talking about. It doesn't affect the image or image quality, but I'm curious what it is.

Thanks,

-Isaac

Attached Images

 

[Just1MoreDave]

I strongly suspect element separation. This is what my copy looks like:



The rear two elements in this lens are glued together. The glue can sometimes break down and cause this problem. A professional repair would likely exceed the value of the lens.