Originally Posted by
wickerprints
The problem with your question is that the optical performance of a lens is not uniform across the entire image circle, and consequently, the size of the format has an effect on what potential aberrations you will see. This is why the question of camera body is relevant.
Especially for an ultra-wide angle lens, corner performance is often significantly poorer than the center performance, as is vignetting. However, these issues become less noticeable on a smaller sensor because those aberrations simply fall outside of the sensor's field of view. This is why you cannot simply ask "is it good," because some people won't even see parts of the image circle that the lens is designed to project. Furthermore, the resolution of the sensor itself plays a role in how easily certain aberrations will be apparent, but this is not as significant an issue as the sensor size itself.
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