What is the sigma 15mm f 1 4 dg dn diagonal fisheye art good for?

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From Sigma 15mm f/1.4 DG DN Diagonal Fisheye Art: Sigma 15mm f/1.4 DG DN Diagonal Fisheye Art: A prime lens by Sigma for Full frame cameras, 15mm f/1.4. A fast full-frame fisheye, made with night-sky photography in mind. Specs - Maker: Sigma - Focal length: 15mm (prime) - Maximum aperture: f/1.4 - Made for: Full frame sensors - Mounts: Sony E, L-Mount - Stabilised: no - Autofocus: yes What it frames like - On full frame (Sony E, L-Mount): as marked, 15mm. - On APS-C (Sony E, ...

From Focal length converter: How it works: Multiply the focal length by the sensor's crop factor to get its full-frame equivalent. To go between two smaller formats, multiply by the first crop factor and divide by the second. Crop factors are measured on the sensor diagonal, so formats with a different shape (4:3 against 3:2) frame slightly differently across the width.

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