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Thread: Circular Image Pinhole Camera

  1. #1

    Circular Image Pinhole Camera

    Hello...

    I want to build a pinhole camera that makes circular images...

    I'm thinking it will be based around an 8x10 film holder...

    How do I figure out what size pinhole and the distance I have to mount it from the film plane, in order for it to be a circular image?

    Thanks for your help!

  2. #2

    Circular Image Pinhole Camera

    There are 2 ways to do this; you can place a circular mask (made of cardboard or heavy black paper) directly in front of the film holder; with a normal angle of view pinhole this will give circular images with a constant exposure out to the edge. This will resemble the first Kodak Brownie paper rollfilm cameras in the 1890s, which created circular images using such a mask.

    The other way to make a circular image is to have such a short projection length that the image is totally vignetted around the edges. This method won't give a sharply defined circle; rather, the central image will gradually fade out to black. I would guess that a projection length of about 2" from pinhole to film holder would give an angle of view around 126 degrees; this might work for a negative 8" wide. If the image doesn't fade out quickly enough, shorten the projection distance to 1.5" for an angle of view around 138 degrees.

    ~Joe

  3. #3

    Circular Image Pinhole Camera

    I think that a good way to get quick fading out by vignetting would be to make what is not recommended in pinhole photography : to drill a hole in a material of "not negligible thickness".

    For instance, drilling a hole of 1mm diameter in a 1mm thick material would cut off entirely the light for incidences of more than 45 from the optical axis.

    Varying diameter and thickness would give any vignetting angles at will.

    Paul

  4. #4

    Circular Image Pinhole Camera

    But do you get an image with a thick pinhole material?

  5. #5

    Circular Image Pinhole Camera

    Yes, and you should call it "tunnelhole photography"

    Attached files

  6. #6

    Circular Image Pinhole Camera

    And may I predict an even more interesting effect ?

    Progressive tangential scattering ;D

    Paul

  7. #7

    Circular Image Pinhole Camera

    BTW, Jeremias, there are far fewer people who come over here to read the ALT forums. They are more lens-oriented (but not exclusively).

    You got some quick replies, but some posts sit here for days before anyone notices or says anythig.

    Alot more activity on the pinhole side...

    Murray

  8. #8

    Circular Image Pinhole Camera

    Unless you are using Polaroid materials and want to display the orginal, why not just crop the image in printing or scanning? Most image-processing programs allow a circular (or square, or elliptical, or whatever) mask over the image, and the edge can be feathered if you don't like a sharp edge. That way you can adjust the mask to suit the image, instead of trying to frame in-camera to suit a mask you can't see.

    If you do wet-darkroom prints, a mask over the printing paper works the same, and you can feather the edge by lifting the mask and moving it up and down slightly during the print exposure. If you're contact printing just put your mask on the light source side of the negative/print stack. If you want the area outside the image to be dark, just make a dodging mask in the shape you want, then make a burning exposure to the area outside the mask.

    Finally, if you do want to mask in-camera, a circular mask in FRONT of the pinhole allows you to change the shape or size of the mask at will (pinhole only - won't work with a lens). A simple way would be to use a Cokin filter holder, but instead of slide-in filters just use an opaque "filter" with your mask opening cut in it. You would have to be careful to make sure the mask is centered over the pinhole, however. A commercial matte box would also work, and these days are probably available for next to nothing or you could make one.

  9. #9

    Circular Image Pinhole Camera

    Instead of all this work about making masks or using software to make a circular image why not just construct a camera that will make a circular image at the outset?
    Here is one of the cameras that I began using some 15 years ago; all of the ones that I use are of the same design, the only variation is the length of the cans. They range from about 4 inches for the wide angle, to the 'tele' version of ~ 7 inches focal length. SInce the rim of the can butts up against the 4x5 inch B&W film the image is a circle, and no messy fall-off to clean up after... :K)
    For an 8x10 sheet size just use a larger institutional food supply can - do empty the beans out first, unless you want VDB as the 'native' toning. You would have to use a 8x10 film box of course with the tripart box for light baffling, but you could cut away part of it to insert the film holder. I just use them with 1 sheet in a box and go out with 15 of them loaded in my darkroom.
    Someone once asked me what I would do if I won the lottery. My reply, 'get bigger cans...'
    Peter Attached files

  10. #10

    Circular Image Pinhole Camera

    OH, I forgot to add that the black circle is the result of my filing out the 4x5 film support so that it sits flat in my D2V enlarger. This came out my my 35mm street photography practice of showing the whole of the frame. I continued this for several years as a proof that though I used no viewfinder, it was possible to sight the camera on my tripod and get an exactly composed image and one in which the near foreground was not empty space but an integral part of the composition and used the complete depth of field that is pinhole work's essential characteristic. After some time I was satisfied that I had proved that element of the task that I set myself, so now I use a slightly smaller support that allows maybe a mm of cropping to tighten up the composition. The image size from each of the 3 types of cans varies from about 3 1/8 to 3 3/8 inches on the 4x5 film.

    Attached files

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