4x5 pinhole help

[Pinholethrowaway]

Hey, everybody (: I posted a while back about a friend giving me his old 4x5 pinhole camera. I love using the ~f/280 lens that's on it, but now I'm interested in getting a new lens with an Aperture of f/2000 for a project that is very very bright with artifical lights.

Right now the stats of the 4x5 pinhole are:
An F stop that is somewhere between f/276 and f/287
A lens diameter of .018inches (.46mm)
A distance between the lens plane and the film plane of 5 inches

I guess my questions are:
1) what diameter lens would I need to get to f/2000?
2) And what would that do to my field of view?
3) Would it be easiest at this point to just slap on an ND filter?

Thank you all so much in advance ❤️

[Havoc]

I'd go for 3, if needed combined with slower film.

[tonyowen]

suggest program "Pinhole Designer" which enables all variables to be considered
regards
Tony

[Jim Jones]

The present pinhole diameter is near optimum for that focal length. The optimum diameter depends on focal length. The more the diameter deviates from optimum diameter, the less sharp the image will be, although the field of view will not be greatly changed. A ND filter is the best option. I've also tried B&W film, fully exposed and developed. placed in close contact with the fresh film.

[reddesert]

You have an f/280 pinhole. You want to get to about f/2000. This is about a factor of 7-8 in f-number, which is about 6 stops of exposure. You need two 3-stop ND filters, or something like a red filter and a 3-stop ND filter.

An f/2000 pinhole will be unsatisfactory. There are two reasons.

1. f-number is focal length divided by pinhole diameter. Your focal length is 5 inches = 127mm. You will need a 0.06 mm pinhole. This is not easy to manufacture and it would need to be in a sheet of material that is less than 0.06mm thick to avoid vignetting (mylar?)

2. The images from a f/2000 pinhole will be lousy due to diffraction. The blur circle due to diffraction is roughly 2 * f-number * wavelength of light. Use about 500-550 microns for wavelength of green light. For your f/280 pinhole, the blur circle is about 0.28 mm, which will make a reasonable contact print. For the f/2000 pinhole, the blur circle is about 2 mm, 8 times larger, which will look really blurry.

[paulbarden]

The present pinhole diameter is near optimum for that focal length. The optimum diameter depends on focal length. The more the diameter deviates from optimum diameter, the less sharp the image will be, although the field of view will not be greatly changed. A ND filter is the best option.

This is good advice, and Jim is quite correct: smaller hole size will only result in loss of sharpness. You have nothing to gain by making a smaller pinhole.

[Pinholethrowaway]

Seriously floored by the wonderful responses. Thank you all for taking the time to answer my crazy pinhole questions!!! :D