making pinhole aperture for SLR
I'm very new to pinhole photography. I'm trying to mounted a pinhole aperture opening on a body cap for my SLR by drilling a hole with a sewing needle into a thin brass shim (as described in Jim Shull's intro pinhole book).
I've been able to get images with objects in focus up to about 20 feet away; beyond that they get blurry. I'm not sure if I need a larger pinhole, smaller pinhole, or a hole that is drilled "cleaner." Shull's book claims I can get a clean pinhole opening with this method, but I'm not sure its working. Any suggestions?