Carl Zeiss Jena Flektogon 20 mm f/ 4 Lens

This is a very sharp lens and the images are saturated with beautiful colors. Small and lightweight. I use it for Landscape photography on my Sony a7Rii.

Weaknesses:

It is dificult to focus because the focus ring is big and in my copy not very smoth. I don't think is a good walk around lens but excellent for landscape photography.

Comments:

I got my at a very low price, it was mounted in an Exakta camera. The camera was damage, but I opened the lens and fixed,  (it was missing the rubber that goes on top of the focusing ring, I bought a generic one and was able to use it with good results) I manage to salvage the lens and I have used it with excellent results.

Incredible picture quality. You can shoot at 15 cm. No optical distortion. Small size and weight.

Weaknesses:

Construction is not very reliable, although of course much better than the modern plastic. Not too smooth focusing. Expensive 77mm filters. Without the hood catch glares.

Comments:

Almost a perfect wide-angle lens. It's great to use for shooting HD video on a Canon 5D mark2.

The quality of images compared with the Canon 17-40 L (sharpness in the center and edge, contrast, vignetting, distortion). With a wide margin Flektogon win in all parameters.