This is probably the cheapest decent wideangle lens available. I paid $120 for it on ebay and it came straight from Russia. While it is a fisheye, it can be converted to a rectilinear image using a Photoshop plug-in like the free PTLens.

This is also a manual focus lens, which is extremely difficult to focus accurately because you can't see all the tiny details at 16mm!! The quality of the lens is not superb, but it will do the job in a pinch when you need a cheap ultra-wide angle lens.

I used a Canon 1D (Auto White Balance mode) on a tripod with autofocus and 2 second timer delay to prevent shake. The purpose of using the autofocus was to test the consistency of the focusing. Due to errors in focusing consistency, some pictures came out of focus (OOF) and were useless for comparing sharpness.

Zenitar 16mm f/2.8 Manual focus
f/2.8 "Near"	f/2.8, "Far"
f/3.2, "Near"	f/3.2, "Far"
f/4.0, "Near"	f/4.0, "Far"
f/5.6, "Near"	f/5.6, "Far"
f/8.0 "Near"	f/8.0, "Far"
f/11, "Near"	f/11, "Far"
f/16, "Near"	f/16, "Far"
f/22, "Near"	f/22, "Far"
f/8, Corner at near focus	f/8, Corner at far focus

Notes on Sharpness

Near:
• Sharpness picks up around f/4
• Unlike my auto-focus, auto-aperture lens tests, there is no color shift at different aperture values.
• Chromatic abberation in the corners is very well controlled (on the 1.3x 1D).

Far:
• Sharpness picks up around f/5.6
• I was unable to get more than a gray square in the center of the chart with the 1D! I'm not sure if this is the lens's fault of the 4MP resolution of the 1D.
• Again, chromatic abberation in the corners is very well controlled (on the 1.3x 1D).