[maxe]

Since I own a Sony a65 and was looking for a fast lens, I came across the T* Distagon 24mm F2 of Zeiss. I’ve decided to buy a used one in good condition and was happy until I noticed something while testing:

https://drive.google.com/file/d/18V03ljC...drive_link

It seems like there is a circle where the optical resolution is much lower than in the rest of the picture (at least I assume it’s a circle because the dunes in the foreground are out of focus, so they’re blurry anyway...). Does someone have an idea what can cause this or have experienced this? The seller assured me that the lens have never been dropped or anything. I was using a UV filter (just as protection), but without this still occurs. The front and back lenses also looked fine. I’m considering having the lens repaired but I’m unsure whether it’s worth it.

Here the original file:

https://drive.google.com/file/d/1xnMp6sw...sp=sharing

[toni-a]

Looks like field curvature ...
What is Field Curvature? (photographylife.com)

[Klaus]

Hmmh, at f/4 and infinity focus, the field curvature shouldn't be a huge issue anymore on an f/2 lens.
And the blurriness on the left side seems to be more pronounced? It's hard to tell with this scene, though. Subjectively, this looks fishy to me.
Maybe take a shot of some (image-covering) buildings from the other side of a street at various apertures.

[maxe]

https://drive.google.com/drive/folders/1...sp=sharing

@toni-a @[b][b]Klaus [/b][/b]Thanks for your replies. I took some pictures of a building today, also a bit closer for a more uniform image. I hope this helps.

I’ve also noticed that when testing for dust particles on the lens, a small barely visible dark circle shows up in the center of the image when using F2 and focussing to ∞. When stopping down, it disappears. I’m not sure if it’s related to the sharpness-problem or a normal optical phenomenon.