I've tried a few shots with a pinhole in a rangefinder body cap. My pinhole was from a set in stainless steel by Eric Renner at pinholeresource.com, sized 0.0087 inches, where the web site mentioned above recommends 0.009 inches for the focal length of my setup, which is 28mm. This works out to about f:130.

I don't have a lot of shots with this, but you can see one (without much in the distance) at:

http://www.oberlin.edu/observatory/DomePinhole.jpg

The pinhole/camera is at:

http://www.oberlin.net/~lee/BessaPinhole.jpg

You can see that I blacked out the pinhole with a Sharpie permanent marker to cut down on reflections and flare. Hope this helps as an example of what to expect.

With an SLR, and its longer film-to-lens-flange distance, you'll want to use a different sized pinhole, as the diffraction limit that determines optimum pinhole size will allow you to use a somewhat smaller f:stop, perhaps in the f:150 to f:200 range. There are some lists on the web that have film-to-lens-flange distances that you can plug into the mrpinhole calculator, but I couldn't find a really comprehensive one in a quick search.

Hope this helps.

Lee