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  1. #11
    Ed Sukach's Avatar
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    Quote Originally Posted by ilona
    Thanks Ed! I didn't realize until I read your message that this 85mm film dimension was the diameter absolutely needed by the film. But of course, the diagonal is also the diameter...
    You lost me here. The diagonal of a "6cm x 6cm" (actually a lot closer to 5cm x 5cm ... measured it) frame is about 70mm and that would be the necessary image circle. An 85mm focal length, with an image circle of 163mm is considerably more than necessary. OK to have more than you need, not good - at all - to have less.

    However, my previous question was also about "what is a safe margin between the diameter absolutely needed by the film (or diagonal) and the diameter of the image produced by the hole (or coverage)": 1cm, 2cm, 4cm extra on each side???
    I don't have an answer to that. It depends on how much "fall-out" (dimness at the extremes of the frame) you consider to be acceptable. Some will tolerate - or even WANT more than others.

    I can only suggest that you try it - and see what happens - which is pretty much what is necessary in pinhole photography anyway.
    Carpe erratum!!

    Ed Sukach, FFP.

  2. #12

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    Ilona,
    This image was taken with my 80mm rollfilm pinhole camera. The lab cropped the sides a bit to make a 4x5 print but the negative doesn't show any fall off. The 57mm camera works just as well. I'm sure that if your camera's "focal length" falls within the two you'll be satisfied with the coverage. I'm planning on building a new camera as wide as the physical limits allow. The diameter of the film spool is about an inch; plus 1/8" for clearance makes it in the 30 to 35mm range. If there's fall off.....who cares? It's a pinhole camera.
    Attached Thumbnails Attached Thumbnails FortPierceInlet.jpg  
    Last edited by ElrodCod; 04-25-2005 at 10:02 PM. Click to view previous post history.

  3. #13
    ilona's Avatar
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    I'm going to give that 85mmm focal length a try and we'll see! As you said, it's pinhole photography ;-)
    I'll be curious to get news about your new camera, ElrodCod. You'll post updates in the forum, I guess.

    Thank you all for your useful tips and input!!!

  4. #14
    Donald Qualls's Avatar
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    FWIW, I've seen pinhole images done on 8x10 film with a focal length under 30 mm, which cover the whole frame (albeit with light fall-off in the corners like a Holga, but still printable and with detail recorded over the whole frame). The field of view limitation for a well-made pinhole is more likely to be from vignetting by parts of the camera than by light fall-off; most negative film will let you overexpose the center by one to two stops, and underexpose the edge by one stop, and still produce an image that just needs a little dodging and burning; with reduced EI, low-contrast development, darkroom manipulation and the right film (like 400TX), you can get away with still one more stop of difference, which would be equivalent to a 4:1 path length difference between center and corners of the frame.

    On 6x9 cm, you could probably get away with a 35 mm pinhole, if the camera were carefully made to avoid vignetting. 45 mm isn't at all uncommon, and though the exposure will vary too much over the 6x9 frame for slide film, not many folks shoot 6x9 slides anyway.
    Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.

  5. #15

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    I agree with Donald. I've read (can't remember where) that the image circle formed by a pinhole is three and a half times the focal length. The image circle calculator on the Mr.Pinhole site uses a factor of 1.92 which, IMO, is quite conservative.

  6. #16
    ilona's Avatar
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    Indeed, I noticed that the results given by mrpinhole.com and the Pinhole Designer software were quite different.

  7. #17
    ilona's Avatar
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    I found another calculator on the web: http://www.stanford.edu/~cpatton/pin...alculators.htm (for Windows).

    I didn't try it yet.

  8. #18

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    Quote Originally Posted by ilona
    I found another calculator on the web: http://www.stanford.edu/~cpatton/pin...alculators.htm (for Windows).

    I didn't try it yet.
    I have that one too but I don't find it as useful or as easy to use as the Pinhole Designer.

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