How can I tell what image circle a lens covers?
Asked 3/16/2018
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Is there an easy way to find out the image circle of a lens without testing it on a larger sensor? For example, I’ve heard some lenses like the Zeiss Otus may project a slightly larger image circle than full frame. Does using only the center of a lens’s image circle on a smaller sensor generally improve corner quality because you avoid the outer edges?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
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You may be able to find published data about the size of the image circle produced by a given lens. In the case of the Otus lens line, the image circle (for all three models, 28mm, 55mm, and 85mm) is about 43mm across, so a bit bigger than it has to be to cover a 35mm sensor, but not nearly big enough to cover a much larger sensor with edge-to-edge sharpness/resolution.
(The size I'm quoting for image circles produced by the Otus is from the datasheets linked here: https://www.zeiss.com/camera-lenses/us/cinematography/products/otus-lenses.html#data)
Originally by user74159. Source · Licensed CC BY-SA 4.0
user74159
8y ago
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Generated from our catalog & community — verify before relying on it.
The easiest way is to look for the manufacturer’s published specifications or datasheets. Some makers publish image circle coverage directly.
For example, the Zeiss Otus lenses are listed at about a 43mm image circle. That’s a little larger than what’s needed to cover full frame/35mm, but it’s not large enough to expect proper edge-to-edge coverage on a much larger format.
And yes: using a smaller sensor only captures the central portion of the lens’s image circle, which generally avoids the weaker outer areas. That often means better-looking “corners” on the smaller format, since those corners come from a better-corrected part of the lens projection.
But a lens having a slightly larger image circle than required does not automatically mean it will cover a much bigger format well. Coverage, sharpness, illumination, and aberrations at the edges are separate issues.
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