Optimal pinhole size?

Discussion in 'Pinhole Photography' started by robopro, Nov 6, 2006.

  1. robopro

    robopro Member

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    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?
    Terry
     
  2. PhotoPete

    PhotoPete Member

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    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.
     
  3. Jim Jones

    Jim Jones Subscriber

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    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.
     
  4. 6x6x9

    6x6x9 Member

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    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-Photo..._bbs_sr_3/102-8098902-5106525?ie=UTF8&s=books
    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.
    Best wishes!
    Snjesko
     
  5. Jim Jones

    Jim Jones Subscriber

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  6. Ed Sukach

    Ed Sukach Member

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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).

    ??? Pinholes Work BECAUSE of "diffraction".

    ??? I'm competley lost here.

    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...
     
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  7. robopro

    robopro Member

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    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...
     
  8. robopro

    robopro Member

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    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!

    Doh!
     
  9. 25asa

    25asa Member

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  10. Jim Jones

    Jim Jones Subscriber

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    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.
     
  11. Ed Sukach

    Ed Sukach Member

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    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."
     
  12. robopro

    robopro Member

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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! :smile:
     
  13. crispinuk

    crispinuk Member

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    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: )
     
  14. robopro

    robopro Member

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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
     

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  15. Jim Jones

    Jim Jones Subscriber

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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/SearchResults?sts=t&an=Van+Heel&y=8&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!
     
  16. crispinuk

    crispinuk Member

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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
     
  17. Ed Sukach

    Ed Sukach Member

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    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.
     
  18. robopro

    robopro Member

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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.
     
  19. Jim Jones

    Jim Jones Subscriber

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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.