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What is the correct distance? There are so many different "ideal" distances and hole sizes that trying to get things exact seems to be pointless. What color light do you want to be "in focus"? What correction factor? What is the distance of the object from the "lens"? All these things go into determining the "perfect" pinhole size. Use Pinhole Designer to work out some variations.
My suggestion is get a bunch of different size holes, figure out what the approximate exposure will be, and shoot them all and see what you like best with the film and subjects that you are shooting. And before someone says, well just put an XYZ color filter over the hole so that you are dealing with "monochromatic" light, remember that a pinhole has almost infinite depth of field, so any bit of dust will show up in your image.
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One general thing you can do to improve sharpness is restirct the rameg of sensitivity of your film (or paper). Recall that a pinhole focuses different wavelengths to very different distances... the very antithesis of an apochromatic glass lens. So what you can do is use ortho film or paper, which have mostly blue sensitivity. Once you work out the optimum effective focal length, you will indeed see more sharpness. Some of that sharpness is 'real' sharpness... and some of it is implied by the overall tonality and comes from the contrastier tone separation that you get from the ortho film/paper if you look for the right light. On this point, the very simplest thing you can do to make your pinhole images appear sharper is simply to look out for contrasty light and contrasty edges (e.g. stark shadows etc.). If you do that then you can indeed get results that people won't believe are pinhole images.
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 Originally Posted by Greg_E
What is the correct distance? There are so many different "ideal" distances and hole sizes that trying to get things exact seems to be pointless.
Yeah, many of the simple formulas are based on center green, around 532 nm or so.... because most people don't realize how horribly non-apo a pinhole is. If you want the best results, then, you'd have a film that has sensitivity only right around that point. For this reason, as I just mentioned, I'd dig into the formulas, insert a wavelength in the mid blue, and shoot to ortho film or paper. Done. [N.b. I do realize that some cool effects can be had by shooting to pan film or colour... but I think we're talking about maximum sharpness here.]
Of course, you can also put on a colour filter to restrict the wavelength. That works too. Costs you light though.
Whether restricting the wavelength is as important as looking for contrastier light, well, you be the judge!
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The formulae for optimal pinhole size also favor longer focal lengths, and longer focal lengths imply that, for the same angle of view as your 35mm format pinhole camera, it would require a larger film format, which prints or scans with more detail, due to a lower magnification ratio.
Thus, the simplest way to achieve sharper pinhole pictures is to up-size to a bigger film format.
~Joe
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Can someone list the current ortho films? I spent a little time looking for ortho B/W film in 120 a while ago and didn't turn up much in the way of results. This is about the only way to effectively filter the light without risk of dust getting into the image. Even better if it can be processed with DR5 for positive images. Also must be a slow emulsion for finer/smaller grain.
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Ilford ortho plus, arista aphs, and arista-II. I haven't used any ortho films in 120 format though.
Paper is plenty good for LF pinhole though.
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I am moving towards a lens cap hole holder, and macro extension tubes to get the desired angle of view on my regular lens camera, so paper is out for me. I'll have to see what DR5 says about processing those films, I scan everything and positives scan better than negatives.
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Sharper: 1) Bigger film (build yer own camera!) 2) Sharp pinhole (check it under a microscope, if practical) 3) Flame the hole with soot and recapitulate 4) Restrict a wavelength with a filter 5) Optimize hole to film plane distance, which requires knowing the size of your pinhole.
Wider angle: 1) Move the film plane closer to the hole.
For reference, my f250 cameras have a hole to film distance of about 10 to 11 cm, and that gives about 70 degrees of coverage.
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