I'm just a newbie into pinhole photography but as for the shape of my pinhole, I've tried to get it as round as possible using a needle. For the material, I use the metal from soda cans and sand it down with an electrical orbital sander using 60 grit sand paper. This gets it pretty thin pretty fast. As for the color of the material, I usually paint both sides black. Below is probably the best shot I've done using the methods described.
Originally Posted by Cesaraugusta
The focal length for the camera it was taken with is 125mm and my new 8x10 camera that I built has a focal length of 190mm - which is what sparked the thread. Wanted to know if there was a reason why making a larger pinhole for the longer focal length would be beneficial. I think the pinhole diameter for the above shot was .46mm.