[Toffle]

The optimal pinhole diameter for a focal length of 40 mm is roughly 0.23 mm. So, 0.3 mm is a bit on the larger order, but it will work fine. Most people shoot pinholes for their unique characteristics and not to get optimal sharpness results.

Good luck and don't forget to post some images.

Hi Ralph,
Where did you get your figures? (I don't doubt them) My calculations, from the designer at pinhole.cz came to .282 mm, but I figured .3 was about as precise as I could get without specialized tools.

One problem I have found with my design, is that not all 4x5 film holders are created equal. I built my camera around a holder with a pronounced ridge that keeps the holder in place when you pull the darkslide. Without the tension of a spring back, some holders are prone to slipping out of place. I already have an idea or two to fix things; this has been a tremendous learning experience.