2x3 camera questions

[Barry Kirsten]

Just in time for WWPD, I've had to get my skates on recently. I decided on a design based on 2.25 x 3.25 sheet film holders, which I have several of and a fair quantity of film. Eventually I got it right after planning defects and general effects of old age. I used one of Earl's ems pinholes, 200 microns at 36 mm from film plane, f/180. Despite the building issues I'm happy with the result.
2x3 Pinhole.jpg

One drawback I encountered was that not all film holders are the same. While making the camera I used a holder to ensure that it fitted snugly. When I came to test the finished camera I reached for a holder already loaded with film, a Graflex holder, and found that it wouldn't fit !!! I have three brands Fidelity, Graflex and Lisco. The horror of this required the hasty use of chisel as shown below. The problem is in the light-trap ridge just above the top of the film area, 98 mm from the bottom in the Fidelity and 99 mm in the other two brands. I'd taken a lot of care with light trapping, and even made a door on the back to provide (hopefully) a perfect seal. Silly me for expecting that film holders follow a standard!
2x3 inside.jpg

Anyhow, to my main question: I first made an exposure of some pencils at 10 cm increments from the pinhole to test closest focus point. I think the picture below shows clearly enough without the need of any other pics, that the closest pencil is sharpest. On my computer, big enlargements show that all of the others are less sharp, and more in tune with the overall sharpness of all other areas of the negative.
Pinhole focus test667 web.jpg

I'm puzzled because I would have expected gradual increase in sharpness away from the camera. I'm also very surprised that the camera focuses so close. I obviously have a closeup camera here, which is what I wanted, as I like nature closeups. I wonder if anyone here has ideas or thoughts on this?

Another question: It occurred to me during the above, that such a small aperture might easily become dusty and hence render images less sharp than usual. Does anyone think This is a significant issue?

Thanks for your thoughts.

Barry

[Tom Persinger]

Hi Barry-
first, really nice looking camera! Great work! many of us have used window foam insulation (comes in long strips with adhesive on one side) as a way to create a light tight area area to secure film holders (that unfortunately are often slightly diff. sizes).

Since there is no lens to bend the light to a point of focus, pinhole photography renders all things in an equal degree of "focus." The softness of the image is directly related to the size of the pinhole (there are some other issues, but put simply that's a fairly accurate statement). I'd guess that the varying degrees of focus observed in the pencil image is more of an optical illusion (based on the decreasing size of the pencils) more than anything else.

Dust can and generally is an issue. Those small holes seem to act as a vacuum! I generally attach a cheap UV filter to all of my pinhole cameras to help alleviate the problem. And with BW film I also often use Red, Green, and Yellow filters.

Hope that helps!
Tom

[JoeVanCleave]

Nice looking camera, Barry.

If you make the pinhole significantly smaller than the size recommended by formulae such as Lord Rayleigh's, you will have a camera biased for close focus, the reason being that for subjects far away, the image will suffer from diffraction, while for close-up subjects the smaller than normal pinhole will help compensate for the usual softening of the image caused by the geometric effects of a pinhole too close to the subject.

It's hard to describe in words, but try doing some simple ray-tracing sketches to see what I mean. If the pinhole-to-subject distance is equal to the pinhole-to-film distance, then the blurr size at the film plane is twice the diameter of the pinhole; whereas for subjects near infinity, with parallel light rays, the blurr size is close to the pinhole size itself.

So while a too-small pinhole diameter might degrade the image quality of distant objects due to diffraction, it will improve the sharpness of close-up objects.

The image-softening effects of diffraction are always competing with the image-sharpening effects of geometric projection; the optimal pinhole diameter for any focal length is the best compromise between the two.

I've never known dust to be an issue, but a gentle blast from a can of compressed air once in a while couldn't hurt.

~Joe

[Jim Jones]

. . . I've never known dust to be an issue, but a gentle blast from a can of compressed air once in a while couldn't hurt.

~Joe

Or an ear syringe.

[Barry Kirsten]

Thanks all for the comments. I must admit that I'd become bamboozled by the mathematics, various theories, constants and other formulas. I also looked at the size of pinholes used in commercial cameras and noted that they all seem to be smaller than recommended by various formulae. In the end I decided to take the advice from someone in an earlier post and just see what happens. As I said, for closeup work I'm very pleased with the results from this camera. I will also experiment with different aperture size and possibly end up with several cameras for different purposes. Can I ask what aperture size any of you might use for this format? Thanks again for the helpful comments.

[JoeVanCleave]

Barry, since I (usually) make my own pinholes, getting an exact size is problematic. I measure them by holding the pinhole up to a light, adjacent to a millimeter scale, and estimate, using a magnifying loupe, how many diameters will fit in one millimeter. So it's only approxiamate. That said, if I were making a camera of your focal length, I'd try to keep the size below 200 microns - get a bit more than five diameters within one millimeter. That's my "gut feel", which helps explain why some of my cameras are better performers than others, I try consciously not to make the size too much of a science, more like an art.

~Joe

[banana_legs]

Hi Barry,

I have a camera that uses the little film holders too; mine is 37mm focal length and also has a 0.2mm aperture. I have double-sided film holders, some 6x9 roll film holders and also a few 6-shot Graflex backs that 'fit' the camera; as you have noticed, they all follow a slightly different standard! I have a layer of black felt on the face that the film holder mounts onto that takes up the tolerances between the film holders. I hold the film holder on with velcro straps too which allows me to use the thin double sided holders, through to the much larger roll-film backs.

My camera is made from old MDF floor board and is no-where near as good looking as yours. Well done!

Evan

[Barry Kirsten]

So many good points and ideas in these replies. Thank you all, I'll keep experimenting. I'll post some serious shots soon.