Optimal pinhole size?
I normally use a 35mm SLR camera and primarily shoot Kodak HIE film. I have 8X10 and 11X14 pinhole cameras using paper negatives, but just made both cameras from discarded cardboard boxes and punched the hole myself with a sewing needle in brass shim. I made both just for fun and immediately fell in love with the whole concept:confused.
I'm now designing a permanent wooden camera for shooting 11X14 albumen glass plates (127mm focal length) and I'm going to have a variety of hole sizes ranging from .2 to 1 mm and have the holes laser drilled in a brass plate so I can easily change the pinhole for different lighting conditions and / or effects. Has anybody ever done this or know of a good way to mount the plate so I can accurately select the pinhole while keeping light out of the box?
I know the plate will need to be mounted offset from the center in some type of frame so it can rotate, I need some type of sliding 'shutter', the whole thing needs to be light tight AND I need some way of precisely aligning the pinhole with the center of the negative (before opening the shutter), but I'm having trouble with the exact design.
Anybody have any ideas?
I think that mounting the plates on a disk would give you the best option- I did this on a Polaroid packfilm camera I modded once. Rotating the disk would allow me to "dial in" the pinhole I wanted. Careful spacing of your plates, along with some alignment marks should allow you to keep the hole centered. Since the disk will rotate rather than move, you should be able to construct an effective light baffle pretty easily. I can try to make an illustration of this if my description is confusing.
If you improvise a shutter behind the pinhole, centering the pinhole will be easy. Also, a detent working in notches around a circular rotating aperture plate was used in the early days of photography, and should be simple to improvise.
http://www.pinhole.cz/en/pinholedesigner/ with a user's constant of 1.5 for optimum on-axis sharpness gives a pinhole diameter of about .35mm for blue light. Any smaller pinhole would result in less sharpness throughout the image because of diffraction, and increase exposure time. A somewhat larger pinhole will cause a loss of sharpness in the center of the image, but perhaps better sharpness towards the corners.
If you mount the shutter and pinhole on a lens board like that on some view and press cameras, future changes or experiments with zone plates will be easier.
Terry, I can't help you with a blueprint or "how to" procedure, but I think that this book might make things much clearer http://www.amazon.com/Pinhole-Photog...e=UTF8&s=books
Anybody have any ideas?
If you don't have intentions to buy it, just send me a pm, maybe I could scan a page or two.
Sorry if you don't like Amazon, but that was the first link I found.
6x6x9 links to perhaps the most comprehensive single source of information on pinhole photography. The book is also available in older editions that may contain all the information you need. http://home.online.no/~gjon/pinhole.htm has some interesting information, more good links, and a good bibliography. One of those links, http://www.mines.edu/~mmyoung/PHCamera.pdf, has interesting insight into pinhole photography. http://pinhole.stanford.edu/ has practical information.
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Uh ... could you run that by me again? I'd like to know the rationale for using a factor of 1.5 instead of "Rayliegh"; and why the caluculation for "blue light" instad of the default of 550 nanometers (arbitray center of the "white light spectrum).
=Jim Jones; ... pinholedesigner/ with a user's constant of 1.5 for optimum on-axis sharpness gives a pinhole diameter of about .35mm for blue light.
??? Pinholes Work BECAUSE of "diffraction".
Any smaller pinhole would result in less sharpness throughout the image because of diffraction,...
??? I'm competley lost here.
... a somewhat larger pinhole will cause a loss of sharpness in the center of the image, but perhaps better sharpness towards the corners.
One thing to watch out for ... 127mm is a short focal length for an 11" x 14" format... be careful with providing adeqaute coverage. With a short focal length like this, there is apt to be *considerable"* exposure fall-off at the extremes of the frame.
"Pinhole Designer" is good. Another, more extensive program is "pce.exe" from Stanford University: http://pinhole.stanford.edu/
.. and go to "calcuator". Probably MORE than you want to know...
Last edited by Ed Sukach; 11-08-2006 at 11:47 AM. Click to view previous post history.
Reason: URL Correction
Ed Sukach, FFP.
Actually I used this same focal length on a cheap cardboard camera using paper negatives and had very little falloff, but I like the effect of what I did get. Oddly enough when I use a pinhole design program like the design wizard at http://www.mrpinhole.com/index.php it shows I should use a 452mm focal length and a .9mm pinhole. I haven't started building the camera yet -- still in the design stage, so can I change it. I have to admit I am curious why and how I got such good results with my cheap camera! I don't even know how big the pinhole is -- I just punched a barely visible hole with a sewing needle and sanded it flat...
When I run the same numbers in three different programs I get three different results...
getting off the subject, but...
As this camera is still in the design stage and I'm already using a 'variable' pinhole feature, I decided I might as well add variable focal length as well.
I decided on using a bellows and found a very good description for building one at http://my.net-link.net/~jsmigiel/bellows.html. I'm going to go with a maximum fl of 452mm with a minimum of 100mm.
Also, as to the pinhole, I was thinking about mounting a round .001 shim on a brass washer to stiffen it up, then offset that on the face of the camera on a central shaft with a small knob to turn it, covering the edges with a rubber baffle for a light seal and a stiff sliding brass shim on the inside for the shutter. That turned out to be easier than I thought -- NOW I have to learn how to build a bellows!
Ed Sukach -- I use a user's constant of 1.5 in Pinhole Designer based on a fair amount of practical experimenting. Perhaps Lord Rayliegh derived the factor of 1.9 mathematically. The math in his famous paper on pinhole photography is beyond me. I used blue light instead of white light because the original poster mentioned doing paper negatives. If panchromatic film is used, the default of 550nm would be correct.
"??? Pinholes Work BECAUSE of 'diffraction'". Not entirely true. An oversized pinhole obeys geometric optic rules, and diffraction contributes little to its performance. Resolution in an undersized pinhole is limited by diffraction. According to geometric optics, the smaller the pinhole, the sharper the image. However, as the pinhole is reduced in size, diffraction starts to spread the image. At this critical point, diffraction actually sharpens the image. Then a pinhole can resolve line pairs slightly smaller than the pinhole diameter. Diffraction does interesting things to pinhole images. For example, if you directly view a distant point source of light through a certain small size pinhole, a few thousands of an inch in diameter, the center of the image is dark, not bright. Of course this would be impossible if geometric optics was the determinant factor.
I agree that 127mm is awfully short for an 11x14 camera. If my quick figuring is right, that means about four stops fall-off in illumination in the corners due to the fourth power of the cosine law. There is also a loss of sharpness because, as the off-axis angle increases, the pinhole appears elliptic, not circular, and increasingly undersized. In the 11x14 camera, the problem is aggrevated because the distance to the image corners is about twice the distance to the center of the image. In extreme wide angle pinhole photography, the images display something like astigmatism in the corners: radial resolution is less than tangental resolution. Some pinhole photographers don't seem to be bothered by all of this, though, and produce pleasing images with such cameras.