You asked

Is the viltrox af 9mm f 2 8 air good for astrophotography?

I don't have anything on this site that covers astrophotography specifically, so I can't tell you how the Viltrox AF 9mm f/2.8 Air performs on the night sky. What the page does say is that it's a wide lens: on APS-C it frames like 14mm on full frame, and f/2.8 is its maximum aperture. It's not stabilised, and it's made for APS-C sensors, so it fits Sony E, Fujifilm X and Nikon Z bodies in that crop.

For the framing side of things, the focal length converter explains how crop factor changes the field of view and depth of field. If you're weighing a wide prime for night work, the Viltrox AF 9mm f/2.8 Air page lists every body it fits, and the sensor sizes guide explains why the APS-C crop matters.

Written by Claude from this site's pages.

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