Pinhole size and distance

Discussion in 'Pinhole Photography' started by Darkroom317, May 10, 2010.

  1. Darkroom317

    Darkroom317 Member

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    I know this has likely been covered to death but what would be a good pinhole size for 120 (6 x 7). Also, what would be the distance needed between the pinhole and the film plane?
     
  2. DWThomas

    DWThomas Subscriber

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    Depends on the angle of view you want (or can support if you're modifying a regular camera). There's a calculator on the Mr. Pinhole site that might help (not to mention other info.)

    I used about 0.36 mm with about 90 mm film to pinhole for my SQ-Hole 6x6.

    Pinhole Designer is a Windoze program that can be used to calculate a bunch of stuff too.
     
  3. SMBooth

    SMBooth Member

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    the diameter of the pinhole is (kind of) dependent on the distance from the film plane to the pinhole. I use .3mm at 50mm (f166) for my 6x7 pinhole camera.
     
  4. Lee L

    Lee L Member

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    Can you clarify? Do you mean aperture, as in f-stop, rather than the physical diameter of the pinhole?

    Lee
     
  5. DWThomas

    DWThomas Subscriber

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    The only numbers are the pinhole diameter (it is the aperture) and the pinhole to film plane distance, sometimes called "focal length" although there isn't any focus involved with a pinhole. "Focal length" / Aperture diameter = f-stop.

    There's a fairly long thread back here that touched on a bunch of stuff and has some potentially useful links for the OP.
     
  6. Lee L

    Lee L Member

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    Well, the effective f-stop changes with the pinhole to film plane distance as DWThomas notes.

    So that's three numbers, and the physical size of the pinhole, once made, is not a variable (as implied by SMBooth's wording), but a constant.

    The 'optimal' pinhole size, however, would change with the distance from film plane to pinhole. Perhaps that's the clarification I'm asking for.

    Eric Renner, author of Pinhole Photography and owner of the Pinhole Resource has found over 50 charts from the last 125 years. Although he presents a couple of others, his primary suggestion is:

    A=sqrt(55*F)

    where A = optimal pinhole diameter in thousandths of an inch
    and F = distance from pinhole to film in inches

    multiply A by 0.0254 to get pinhole diameter in mm

    Lee
     
  7. SMBooth

    SMBooth Member

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    Yes there is technically a optimal pinhole diameter for a given distance of pinhole to film plane, once you have that pinhole diameter and distance you can work out the f stop to calculate exposure times.
     
  8. Darkroom317

    Darkroom317 Member

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    So, I tried the equation Lee mentioned and came up with a .3mm pinhole. I then plugged that number in at the Mr. Pinhole site. It would give me a focal length of 50mm. The distance between the pinhole and film plane would be 3 inches.

    Thanks for all of your replies.
     
    Last edited by a moderator: May 11, 2010
  9. DWThomas

    DWThomas Subscriber

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    You lost me here .... the focal length and the distance between the pinhole and the film plane are the same thing. 50 mm is about 1.97 inches - is that 3 a typo?

    If designing a camera from scratch, I would pick a film format, then pick an angle of view. From that you could determine the film plane to pinhole distance, and from that work out the pinhole diameter. Ergo, take a look at the "Design Wizard" on the Mr. Pinhole site. In my own case, I was using existing cameras, so there were some limitations on those starting parameters.

    Edit: Just tried walking through that "wizard" and its behavior is rather strange. It only takes one parameter, seemingly not giving a chance to set anything else before it coughs up a set of numbers based on mysterious assumptions. The calculator button might be a better tool.
     
    Last edited by a moderator: May 11, 2010
  10. Darkroom317

    Darkroom317 Member

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    Ok, thanks. My guess is the numbers are off then

    It gives a waring saying that the image circle will not cover the film. So,I moved the distance until it would.

    Edit: The designer gave me a focal length of 50mm. I checked the distance in my plans an it comes out to 76mm. Which for 6 x 6 would be the same as 50mm on 35mm. The wizard is really confusing
     
  11. grahamp

    grahamp Subscriber

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    I assembled a 5x4 format camera a few weeks ago. The film to pinhole distance is ~39mm, and the pinhole is 0.3mm. To a certain extent the coverage is governed by the thickness of the material used for the pinhole. The thicker it is in proportion to the hole diameter, the smaller the coverage. Then there is also the amount of corner light fall off that you can accept as coverage.

    My first pinhole was too thick, and I had a roughly circular image on the 5x4 film. The current one is much better and has (weak) detail in the corners. I'd say that there should be no coverage problems with a pinhole to film distance close to the 'normal' focal length for the format.

    There's a negative scan of the first image with the camera here: http://grahampatterson.home.comcast.net/~grahampatterson/grahamp/pinhole/jpg/dock-ford-building.jpg The fall-off in a print is not quite as pronounced. You can see the darkslide being used as a shade in the top left corner :cool:
     
  12. bowzart

    bowzart Member

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    So when you moved it so it would cover, you've changed your F to an arbitrary value. Then, you might as just poke a hole and see if it works, because you've invalidated the calculations. If it is supposed to be 76mm, that's the value of F regardless of whether it covers or not. Of course, if you change it to an arbitrary value and can accept the results, it's ok, but you will need to refigure your f/#.

    I've often used the formula in the old Photo Lab Index since I started doing this before Eric published his data. That formula is sqrt( .00007 x F) all in inches. I suspect the formula cited above, by Lee, at .000055, would be as good or better. The difference in the various formulae stems from the specific wavelength of light that the individual chooses as a basis for the calculation. The result is always a compromise between the softening effects of diffraction (becomes more pronounced as the diameter decreases) and resolution (which becomes more pronounced as the diameter increases). Any diameter within the range between Lee's quotation from Eric and mine ought to be good. As for the wavelength of the light, I don't bother with it, although I suppose I ought to consider it.

    The other factor which nobody seems ever to consider (although grahamp alludes to one aspect of it) is the quality of the physical hole. You can have a hole that agrees with the math and still produces crummy images because it has ragged junky edges and most likely forms a rough tube through metal that is too thick. A nice clean hole with sharp edges will give the best results.
     
  13. RalphLambrecht

    RalphLambrecht Member

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  15. SMBooth

    SMBooth Member

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    for any given pinhole diameter there is a focal length, a .39 pinhole is suitable for your 76mm camera weather its 6x6, 35mm or 4x5. If you have a .3 pinhole then your correct pinhole to film plane is 45mm. As you use larger formats the light falloff at the edges is greater.
     
  16. Lee L

    Lee L Member

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    Poorly stated again to the point of falsehood. A pinhole has no focal length, as it doesn't focus. It has a pinhole-to-film distance.

    For any given pinhole diameter, there is a range of pinhole-to-film distances that gives a reasonably good balance of point spread and diffraction. Theory also often assumes a perfectly made pinhole in an infinitely thin material.

    See bowzart's post for other considerations that need to be taken into account.

    Lee
     
  17. DWThomas

    DWThomas Subscriber

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    OK, I ran through some numbers ...

    Typically a focal length equal to the diagonal of the film frame is provides a "normal" lens field of view.

    Using the square root of the height squared plus width squared for a 6 x 7 frame comes out to about 9.3 cm = 93 mm for the frame diagonal dimension. The angle of view is about 53º.

    Going into Pinhole Designer with a focal (pinhole to film distance) length of 93 mm, using 1.9, Rayleigh's constant, in the calculation, I get a pinhole diameter of 0.43 mm, which results in an effective aperture of f216.
    If I use the constant of 1.6, which some folks use, I get a pinhole of 0.36 mm for f258.

    For a bit wider angle by using a focal length of 60 mm -- approx 75º angle of view, I get a 0.35 mm pinhole diameter (f171) with the 1.9 constant. And 0.29 mm pinhole, f207, with the 1.6 constant.

    Even wider, using 50 mm focal length -- approx 85º angle, I see 0.315 mm pinhole diameter (f159) with the 1.9 constant, and a 0.265 mm pinhole (f189) using a 1.6 constant.

    In all, I used the PD default of 0.00055 mm for the light wavelength (green == mid-spectrum). Note that anything using numbers between those pairs of results will work, and indeed numbers some distance outside will also work to some extent. It's not a real tightly defined situation.
     
  18. RalphLambrecht

    RalphLambrecht Member

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    I agree with your calculations, but have a couple remarks:

    There is such a thing as a Raleigh's constant, but it has nothing to do with Pinhole photography:
    http://hal.archives-ouvertes.fr/docs/00/21/39/53/PDF/ajp-jphyscol197132C1135.pdf
    I think what you're referring to is simply the square root of the Airy disc's diameter (square root of 2.44 or 3.66, respectively). One maximizes sharpness (2.44). The other maximizes resolution (3.66).

    You correctly referred to the angle of view, which is calculated from the negative-format diagonal and the focal length, but we need to make sure that we are not confusing it with the 'actual' angle of view, which is highly dependent on the thickness of the pinhole material and responsible for the image circle? (see attachment)
     

    Attached Files:

    Last edited by a moderator: May 12, 2010
  19. Lee L

    Lee L Member

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    I would agree with you that DWThomas correctly describes 'angle of view' as a product of film size and pinhole-to-film distance.

    I think it's misleading and confusing to also call the restriction of the light path by the thickness of the pinhole material the 'angle of view'. Why use the same term for two entirely different effects? In my view the effect of the pinhole material thickness would much more accurately be described as 'angle of coverage' if we're choosing terms analogous to lenses.

    Lee
     
  20. RalphLambrecht

    RalphLambrecht Member

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    Yes, I agree with that. That's more consistent. I will change my notes accordingly.
     
  21. DWThomas

    DWThomas Subscriber

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    Enh, this is how the world works .... maybe another decade or two of instant worldwide communications will clear some stuff up. In Pinhole Designer, there is a pull-down for that constant value. One of the choices is "1.9 Lord Rayleigh." I was under the impression that he gets credit for the number, but can't say I've ever delved into it at any detail and may have misspoken. Anyway, perhaps I should say:
    That is a good point about the angle of view business. The numbers I posted were from using Pinhole Designer, but I'm sure it is based on the "perfect pinhole," an infinitesimally thick sheet of absolutely opaque non-reflective material with a perfectly round hole (since it's infinitesimally thick, it's got a knife edge for sure. :D As anyone who has tried it well knows, the ideal is only a goal and some of us don't get anywhere close to it. And at the minimum, the light fall-off is an issue of the hole becoming a narrower and narrower ellipse viewed from an angle off the pinhole to film axis, eventually a (closed) line at 90º. But that too can be complicated by the actual fabrication.

    Anyway, the calculations I suggested above were to illustrate my approach to the original poster's question. You have to pick some basic parameter(s) and work out the rest. When I did my pinhole body cap for the SQ-A, the film format and film to pinhole spacing were pretty much fixed, so there was no point in agonizing over angle of view calculations, other than to learn what it was.
     
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  22. Joe VanCleave

    Joe VanCleave Member

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    I believe there's a thread over on F295 where someone went and calculated what the actual off-axis focal ratio and light falloff would be when taking into account a pinhole made in an actual material of finite wall thickness which, when viewed from an angle, appears to be elliptical, due to the real-world wall thickness of the pinhole material.

    It's a great exercise in geometry and math, but really doesn't effect my personal pinhole photography, which I do by imperical testing rather than through calculation.

    As for an "acceptable" angle of view, this is really an aesthetic choice that an online spreadsheet can't decide for you. Some people like the "Holga-like" dark corners, or whacked-out extreme wide-angle views, while others like their images more serene and even-exposed from center to corner.

    I think it's an interesting technical challenge to determine all the parameters of a pinhole camera and image ahead of time, but that doesn't really make us better photographers, nor do such calculations inform us about aesthetic choices that only we can make for ourselves. The great thing about pinhole photography is that there's no "right" or "wrong" approach, so the idea of hard, fast, fixed rules is a misnomer. Sometimes the best pinhole images are the ones resulting from the most spontaneity, with the least amount of preplanning.

    ~Joe
     
  23. DWThomas

    DWThomas Subscriber

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    Actually, even with zero thickness the pinhole appears elliptical from an off axis view; the finite thickness only increases the problem. In truth, I'm in basic agreement with the idea that it's not necessary to calculate the stuff to death, just put something together and take some pictures. I view it a bit like cooking/baking without a recipe, sometimes it's fun to blur some boundaries!
     
  24. RalphLambrecht

    RalphLambrecht Member

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    Agreed, but I like to understand the facts before I ignore them.
     
  25. Lee L

    Lee L Member

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    I feel the same way. I think the difference across a range of pinhole sizes won't optimize an image to the point of making it succeed or not as an image worth looking at. Finding some discrete optimal pinhole size is an exercise in math and theory, not making significant photos, even if you can define precisely where along some spectrum your optimum image quality lies.

    I also think there are many other, more interesting things about pinholes to explore, along with slit apertures, zone plates, and other lensless image forming methods. I recently acquired a handmade pinhole from bowzart that I'm hoping to have time to work with this weekend (if I can get out from under other chores and mount it), and the subject matter and other considerations are more important to me than whether it might be possible to get a 5% increase in 'sharpness' from a pinhole. One of those is the fun of using a tool expertly hand-made by a friend.

    That being said, the OP does deserve some reasonable answers to his questions, and I think he's gotten that.

    Lee
     
  26. Joe VanCleave

    Joe VanCleave Member

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    Yes, of course you're right; I poorly worded my response (or is that "worded poorly"...).

    In case anyone's curious, here's the thread over on F295 that talks about "exposure mapping", which morphs into a discussion about real-world pinhole "tunnels" vs 2-D imaginary pinholes, and the difference it contributes to off-axis exposure.

    ~Joe