Screw this item onto the front of your lens, and you're photographing
90 degrees from where the camera is pointing. The false "lens" on the
front looks believable, but the pictures are actually taken from the
side. Shots are candid because subjects don't realize you're
photographing them.

This is a high-quality Asahi (Pentax) Right-angle Lens Adapter which
fits any lens that accepts 67mm filters. You could use an adapter if
your lens accepts smaller-size filters, but I wouldn't go with larger
filter-size because of possible vignetting.

This was made for a medium-format film camera, but it should work
just as well with digital cameras, large-format cameras or any normal
or longer focal-length lens. (Wide-angles might vignette)

http://cgi.ebay.com/ws/eBayISAPI.dll...m=330023903153