Pinhole size and distance

[Darkroom317]

I know this has likely been covered to death but what would be a good pinhole size for 120 (6 x 7). Also, what would be the distance needed between the pinhole and the film plane?

[DWThomas]

Depends on the angle of view you want (or can support if you're modifying a regular camera). There's a calculator on the Mr. Pinhole site that might help (not to mention other info.)

I used about 0.36 mm with about 90 mm film to pinhole for my SQ-Hole 6x6.

Pinhole Designer is a Windoze program that can be used to calculate a bunch of stuff too.

[SMBooth]

the diameter of the pinhole is (kind of) dependent on the distance from the film plane to the pinhole. I use .3mm at 50mm (f166) for my 6x7 pinhole camera.

[Lee L]

the diameter of the pinhole is (kind of) dependent on the distance from the film plane to the pinhole.

Can you clarify? Do you mean aperture, as in f-stop, rather than the physical diameter of the pinhole?

Lee

[DWThomas]

The only numbers are the pinhole diameter (it is the aperture) and the pinhole to film plane distance, sometimes called "focal length" although there isn't any focus involved with a pinhole. "Focal length" / Aperture diameter = f-stop.

There's a fairly long thread back here that touched on a bunch of stuff and has some potentially useful links for the OP.

[Lee L]

Well, the effective f-stop changes with the pinhole to film plane distance as DWThomas notes.

So that's three numbers, and the physical size of the pinhole, once made, is not a variable (as implied by SMBooth's wording), but a constant.

The 'optimal' pinhole size, however, would change with the distance from film plane to pinhole. Perhaps that's the clarification I'm asking for.

Eric Renner, author of Pinhole Photography and owner of the Pinhole Resource has found over 50 charts from the last 125 years. Although he presents a couple of others, his primary suggestion is:

A=sqrt(55*F)

where A = optimal pinhole diameter in thousandths of an inch
and F = distance from pinhole to film in inches

multiply A by 0.0254 to get pinhole diameter in mm

Lee

[SMBooth]

Yes there is technically a optimal pinhole diameter for a given distance of pinhole to film plane, once you have that pinhole diameter and distance you can work out the f stop to calculate exposure times.

[Darkroom317]

So, I tried the equation Lee mentioned and came up with a .3mm pinhole. I then plugged that number in at the Mr. Pinhole site. It would give me a focal length of 50mm. The distance between the pinhole and film plane would be 3 inches.

Thanks for all of your replies.

[DWThomas]

You lost me here .... the focal length and the distance between the pinhole and the film plane are the same thing. 50 mm is about 1.97 inches - is that 3 a typo?

If designing a camera from scratch, I would pick a film format, then pick an angle of view. From that you could determine the film plane to pinhole distance, and from that work out the pinhole diameter. Ergo, take a look at the "Design Wizard" on the Mr. Pinhole site. In my own case, I was using existing cameras, so there were some limitations on those starting parameters.

Edit: Just tried walking through that "wizard" and its behavior is rather strange. It only takes one parameter, seemingly not giving a chance to set anything else before it coughs up a set of numbers based on mysterious assumptions. The calculator button might be a better tool.

[Darkroom317]

Ok, thanks. My guess is the numbers are off then

It gives a waring saying that the image circle will not cover the film. So,I moved the distance until it would.

Edit: The designer gave me a focal length of 50mm. I checked the distance in my plans an it comes out to 76mm. Which for 6 x 6 would be the same as 50mm on 35mm. The wizard is really confusing