What are the alternatives to the pentax hd da fish eye 10 17mm f 3 5 4 5 ed?

Here is what the site says about that.

From Pentax HD DA Fish-Eye 10-17mm f/3.5-4.5 ED: Pentax HD DA Fish-Eye 10-17mm f/3.5-4.5 ED: A zoom lens by Pentax for APS-C cameras, 10-17mm f/3.5-4.5. A fisheye zoom; the older smc version has the same optics. Specs - Maker: Pentax - Focal length: 10-17mm (zoom) - Maximum aperture: f/3.5-4.5 (it gets darker as you zoom in) - Made for: APS-C sensors - Mounts: Pentax K - Stabilised: no - Autofocus: yes What it frames like - On APS-C (Pentax K): like 15-26mm on full frame; ...

From Portraits: The camera: What matters most is eye autofocus, which current mirrorless cameras do very well: it finds the nearest eye and tracks it, so wide apertures stay sharp. Full frame gives you more background blur at the same f-number than APS-C, but a fast APS-C lens closes most of that gap for far less money; see sensor sizes.

Quoted from this site's pages.