Question about optimal focal length for a pinhole camera

[freedda]

I bought a set of pinhole aperture plates, and I'm trying my hand at building a pinhole camera. On the included info. sheet it lists 'Optimal Focal Length' for each of the aperture sizes. Is this the optimal distance between the pinhole aperture and the film? Or, if not. ?

 

[revdoc]

It's exactly that distance, but you don't need to obsess about getting that distance exactly right. Close enough will do.

 

[Jim Jones]

The sharpness of a pinhole photograph is proportional to the diameter of the pinhole: the smaller the correctly sized pinhole, the sharper the image. This means short focal lengths and wide angle coverage provides the sharpest image. I once used a 24 foot long pinhole camera to photograph a solar eclipse with a pinhole about .075 inches in diameter. The edges of the sun were blurred by nearly that amount. That's an awfully fuzzy photograph!

 

[M Carter]

The pinhole calculators on line are handy - sometimes the optimal hole size + focal length won't cover a given film size. When I built mine (converted Isolette), to go really wide meant the image circle was like 5cm for 6x6 film. I ended up with sort of a "pinhole zoom", where I can adjust the position of the "lens". But to go really wide, there's a circle with the image, surrounded by black. But still seems like I'm about 40-50mm which is fine for me.