You didn't describe exactly how you made the pinhole, the actual mechanics may affect the quality. The method described here has produced the best results for me. I have used #600 grit wet-or-dry sandpaper wet, with gentle pressure and circular motion to do the sanding. My last one was blackened with a liquid used in making brass model railroad parts (some sort of sulfide chemical).
You didn't describe exactly how you made the pinhole, the actual mechanics may affect the quality. The method described here has produced the best results for me. I have used #600 grit wet-or-dry sandpaper wet, with gentle pressure and circular motion to do the sanding. My last one was blackened with a liquid used in making brass model railroad parts (some sort of sulfide chemical).
I made mine by hand as well. sanding the aluminium before and after making the hole.
I think you should try to get it sorted on 35mm for a start there's no reason why you couldn't get sharp or at least sharper images on it.
Thumb it may also be that the film is not flat enough like curling and sagging my thoughts for what they are worth.
Is the pinhole size the optimum for this format?
the shots in the gallery you posted look to me as if they were shot with medium format -- 120 film. For yur homemade camera, don't be afraid to experiment -- make another pinhole -- for small format it is more important to have a very small hole and a very round one, so experiment with perhaps drilling one in aluminum from a soda can and filing the edges so it is smooth. Use a needle for a drill and be patient.
It is also very difficult to have too much black tape on a homemade camera, and make sure you paint the inside matt black so there are no reflections. It will take a bit of experimentation, but you'll improve.