LensTip.com

Lens review

Carl Zeiss Distagon T* 25 mm f/2.0 ZE/ZF.2

21 February 2012
Arkadiusz Olech

7. Coma, astigmatism and bokeh

On a smaller sensor of the Canon 50D the coma is not bothersome at all. Even at the maximum relative aperture this aberration is hardly noticeable. More problems you can encounter on full frame but even there the coma level can be described as medium. It is a pity that, on stopping down the lens by 1 EV, this aberration decreases just slightly.

Carl Zeiss Distagon T* 25 mm f/2.0 ZE/ZF.2 - Coma, astigmatism and bokeh

The astigmatism is not corrected in a perfect way because the result of 6% doesn’t deserve to be described so but it can be certainly considered good. Overall, no major reservations.


Please Support Us

The coronavirus crisis has been adversely affecting many businesses and, sad but true, ours is not an exception. Despite that difficult situation we would like to preserve continuity and high quality of publications available on all our websites. Still, we are now aware it might be impossible without additional financial help. That's why we would like to ask all those who visit, read, and care about Optyczne.pl, LensTip.com i Allbinos.com for support - it's enough you send us a small sum of money via PayPal. If a lot people decide to support our websites we think we'll stand a chance and survive next months without any lasting harm. We count on your support and understanding, stay safe and be healthy.

- - - - - - - - - - - - - - - - - advertisement - - - - - - - - - - - - - - - - -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Let’s look at the defocused images of a point-like diode which was put in different parts of the frame and photographed by different apertures.

Carl Zeiss Distagon T* 25 mm f/2.0 ZE/ZF.2 - Coma, astigmatism and bokeh

Also in this case the lens’s performance falls a bit short of perfection. Many images show diversities in the form of concentric rings which signal some problems with the spherical aberration correction. These problems are real- they can be noticed in the resolution measurements as well. When you set the resolution by f/2.0 and reach the best possible result and then reset the aperture to f/2.8 the resolution level doesn’t improve sharply. If you want to see that improvement you must to move the focus ring a bit. This effect might be small but it remains measurable.