It is already sharp at its fastest aperture and maintains very good performance across the entire frame. Centre sharpness is already excellent at f/2.8 with the sweet spot being around f/5.6. The corners are excellent from f/4.
http://www.mirrorlessons.com/2015/07/23/zeiss-batis-25mm-f2-review/
Batis 25mm is clearly superior at wide apertures, across the frame. At f/2, the Batis is slightly sharper in the center, though the Sony also does quite well here. The Sony 28mm catches up a bit by f/2.8, and beyond that it’s very hard to pick between them. In the corner, it’s no contest. While the Batis isn’t tack sharp here, it’s still showing some detail, while the Sony 28mm is just mush in the corners at f/2.
http://admiringlight.com/blog/zeiss-batis-25mm-f2-vs-sony-fe-28mm-f2/
Center and edge are amazingly close from f/2 right through to f/11. Even at f/16 the image still borders on excellent, and it's only at f/22 that the sharpness tails off to being very good in the center and fair to good at the edges. It is still worthwhile to offer f/22 as an option as sometimes maximizing depth of field is necessary.
https://www.ephotozine.com/article/zeiss-batis-25mm-f-2-distagon-t--review-28389
The Zeiss Batis 85mm f/1.8 is an excellent portrait prime lens. You’d expect sharpness to be high across the frame from such a premium optic, and it doesn’t disappoint.
http://www.photographyblog.com/reviews/zeiss_batis_85mm_f1_8_review/
Zeiss Batis 25mm f/2 is amazing wide-angle prime lens. You’d expect sharpness to be high across the frame from such a premium optic, and it doesn’t disappoint. Even with our A7R II test camera shooting 42-megapixle images at high ISOs, detail is exceptionally sharp
http://www.photographyblog.com/reviews/zeiss_batis_25mm_f2_review/
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