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  1. #11
    Ed Sukach's Avatar
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    Quote Originally Posted by Jim Jones View Post
    "??? 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.
    Now you've done it!!! Brought me to the realization that I've GOT to rearrange my bookcase! I'm searching for the Textbook that was the mainstay of the Optic Courses necessary for training to become a "Quality Assurance Specialist" in the "wildly state-of-the-art" (don't ask - most of what they made was Classified) company where I was employed.
    I remember that one of the authors was "Van Heel" - burned into my memory because there was a delightfully stunning secretary there by the same name... When I find the book, I'll identify it (the book - not her) more efficiently.

    In that training "diffraction theory" and its accompanying math was an integral part of "Geometric Optics" - so I don't know where one "set" of mathematics ends and another begins. It is necessary to have diffraction to form an image without a lens ... uh, unless we are considering Electron Microscopy ... and probably other cases where a "sweeping generalization" does not apply.

    True, there IS an optimum pinhole diameter - and the image quality will be lessened with deviations form that diameter - but not because of the "shift" from "diffraction" to "geometric".

    Diffraction theory was not a "take it and sail through" subject. The only subject more difficult, IMHO - and in the opinion of others - was "Polarization."
    Carpe erratum!!

    Ed Sukach, FFP.

  2. #12

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    I have no idea what you just said, but it sounds like you know what you're talking about! But, I still say my photos turned out better than your description indicates they should have. I used a cardobard box about 5 inches deep and made my pinhole with .001 brass shim and a sewing needle. Didn't even try to calculate the size of the hole -- just punched the point through and sanded it down! Kodak B&W paper, held in place with a little masking tape in the corners. Seems to me most pinhole photographers are trying to produce as 'perfect' a photo -- or as close to a lens photo -- as possible -- and most calculators seem designed to do that as well. Anyway, I'm already going to use a rotating variable pinhole 'lens' and re-worked my design yesterday to include variable focal length with a paper and cloth bellows. This will let me have a range of focal lengths from 452mm down to 120mm and 6 pinhole sizes ranging from .42mm up to 1mm-- should produce some interesting results!
    AND I think the pinhole wizard and calculator available at http://www.mrpinhole.com/index.php provides more useful information than the ones on the Stanford site. Sorry -- but thanks for all the information. I am learning a lot! :-)

  3. #13

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    Quote Originally Posted by Jim Jones View Post
    If panchromatic film is used, the default of 550nm would be correct.
    As I understand it 550nm is a compromise, used because it is at the centre of the visible spectrum ?
    Does this mean, if using panchromatic film, that if a coloured filter was used (e.g. Red), and a matching wavelength value used in the calculation (e.g. 700nm) the results would be 'more optimal' (I hesitate to use 'sharp' and 'better' when discussing pinholes). Or is the difference insignificant (the fact that the different 'constants' that are proposed make far more difference to the pinhole size suggests it is ) ?

    Crispin
    (Thinking out aloud again :rolleyes: )

  4. #14

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    OK, here are two photos made with my old 11X14 pinhole camera with a 127mm focal length and unknown pinhole size (very small). I concede they may be sharper with a longer focal length, but according to you guys they should be terrible. ???

    Terry
    Attached Thumbnails Attached Thumbnails yard.jpg   Machine.jpg  

  5. #15
    Jim Jones's Avatar
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    Terry -- Nice photos. The one of the machinery looks, on a computer screen, labout as sharp as you could expect from a large pinhole camera. It's difficult to evaluate computerized versions of analog photos. Some of Edward Westons famous photos were taken with an inexpensive lens modified for very small apertures fairly close to pinhole size. For some subjects extreme sharpness is unessential. This is especially true when other aspects of the photos are well done.

    Crispin -- you are right that the optimum pinhole diameter changes with filtration. The difference is only noticable in close inspection.

    Ed -- The book you are thinking of may be one of these: http://www.abebooks.com/servlet/Sear...kn=optics&x=66 I'm not familiar with any of them, and would rather see the stunning secretary anyhow.

    "True, there IS an optimum pinhole diameter - and the image quality will be lessened with deviations form that diameter - but not because of the "shift" from "diffraction" to "geometric"." I agree that "because" isn't the most precise word here. Many experts are vague when describing pinhole optics in this region.

    ". . .cases where a "sweeping generalization" does not apply. . . ." Good one!

  6. #16

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    Thanks Jim, now that I've recently made a pinhole panel for my Horseman 6x9 ( I can't decide between Holeman or Horsehole) I'll have to have a play varying focal length and using different filtration and see what happens.

    Terry, I like the photo of the machinery, that big cog really seems to loom over one, almost 3D. Whilst I like to find out about the physics behind it, for me the trick with pinhole photography is to just to have fun making the camera and taking the pictures and not worry about the 'science'. If i like the result I'm happy. If anyone else also likes it - bonus ! Good luck with the camera, be sure to report back when it's finished.

    Crispin

  7. #17
    Ed Sukach's Avatar
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    Quote Originally Posted by Jim Jones View Post
    Ed -- The book you are thinking of may be one of these:....
    it was - : "What is Light", by Van Heel A.C.S. and Velzel C.H.S.
    That was a basic cookbook for the classes, taught by one of the better Optical Engineers on board.

    My 'bag" there was mainly in the Optical - Mechanical interface.
    Carpe erratum!!

    Ed Sukach, FFP.

  8. #18

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    Thanks for the compliments. I like my photos even though I doubt they'd win any awards, but it's always gratifying when others like them too. The 'Machine' photo is also my favorite among my earlier large format pinhole work. If I make another print I think I'll burn the right side in a little deeper next time. The 'Back Yard' was developed in Selctol and both were toned in Kodak Sepia toner. The negative isn't quite so ethereal, but, they are both actually very close in sharpness to the attachments. After doing about a dozen or so of these I went to 35mm format with a lens cap pinhole on a Minolta X570. Got some interesting results but could never quite duplicate the 3D look I got with the larger format.
    I've got what looks like a fairly long term project coming up in my job so it may be a while before I get the time to build the new camera but I hope to have it ready by next Spring and I will definitely be showing it off!
    Crispin, go with Horsehole.

  9. #19
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    Crispin, I'd go with Horsehole, too. In these days just after the USA election, it sounds appropriately political.

    Robopro -- If you wrestle with the math, you'll see why pinhole images can show more detail with large format than with 35mm. The relatively longer focal length with a body cap pinhole contributes to the lack of depth and intimacy of your wide angle large format pinhole camera.

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