ProOptic Pro Optic 0.42x Semi-Fish-eye Auxillary Lens,

The Auxiliary Fish-Eye screws directly into the prime lens. Slight curvature, but no distortion takes place if the camera is held level. The wider the lens the more fish-eye effect attained.

As Reviewed in Popular Photography Jan.2002
"Fisheye lenses are expensive. Independent brands go for over $500, and versions from camera makers run about $800 to $2,000-and these are street prices. OK, here's a fun alternatives a front-mounting fisheye converter. These are usually marketed as video converter lenses, but the type that mounts via a Series VII ring will work on most any SLR lens.

We tried the 0.42X Pro-Optic converter marketed by Adorama (www.adorama.com), $39.95 including case and one mounting ring. We mounted it on a 28-70mm f/4 Pentax FA zoom with a Pentax ZX-5n body, and compared results with a real fisheye, Pentax's very groovy 17-28mm f/3.5-4.5 zoom fisheye.

With the Pro-Optic converter in place, we were able to dial the 28-70mm zoom down to a point (around 38mm) where a curvaceous fisheye image filled the frame, corner to corner. (Auto focus and auto exposure worked without a hitch.) Zooming to a shorter focal length resulted in vignetting in the corners.

Here's the fun part: We zoomed the lens down to 28mm and got a circular fisheye image! So why not try this converter on a wider focal length, you ask? Answer: the angle of view doesn't get any wider, the circle just gets smaller.

Pentax's real fisheye, by comparison, produced a considerably wider full-frame fisheye image with no vignetting, and fine sharpness throughout the: frame. The Pro-Optic converter produced decent sharpness at the center, but quite fuzzy images toward the edges.

But hey, for a tenth of what you'd pay for a "real" fisheye, you can get a fun lens that lets you take both full-frame and circular-image fisheye shots-and possibly whet your appetite for the Real McCoy someday."