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  1. #1
    goros's Avatar
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    Some starter questions

    Hi all,

    I'm thinking in building my own pinhole camera out of a biscuit can and I have several questions about it.

    My intention is not to use film, but paper (actually Ilford MGIV RC) therefore, getting a "paper negative". Afterwards, I will get a positive print by contact printing. If I place the negetive print on top of the second paper, emulsion to emulsion, I will get a positive copy but reverse sided (that is, left to right). A solution is to place the negative with the emulsion upwards, then printing through the negative paper. Is there any problem with this way?

    Next question: As I will use a multigrade paper as "film", is there any advantage in using a contrast filter just behind the pinhole, to get a fixed contrast? How long a "standard" exposure would be?

    Now building issues: Which pinhole size would be more or less OK? I will do it with a pin, so there will not be a lot of accuracy, just to get an idea: 1 mm, 2, 5?

    And another one: Once the camera was built, is there any way to calculate the focal length of the hole?

    Thinking about all these things, I have an idea that I don't know if it could be practical. The thing is to use a water lens. Just when the pinhole is open to take the exposure, put a small drop of water in the hole. If the exposure time is very long, the water will evaporate but for a exposure of five minutes it could work.

    Well. too much for the first time.

    Thanks in advance for your help.

    Cheers
    Alfonso

  2. #2
    Ole
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    If you make a print emulsion to emulsion, you will get a reversed print relative to the negative. But the negative is already reversed, so you'll get the print the right way.

    Pinholes tend to be very small - 0.2mm to 0.8mm or so.

    I suggest you read here: http://home.online.no/~gjon/pinhole.htm
    -- Ole Tjugen, Luddite Elitist
    Norway

  3. #3
    goros's Avatar
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    Are you sure? When printing from a neg, it is emulsion-down in the enlarger. If you put it emulsion-up, you will get a symetrical (mirror) image of what you get when it is emulsion-down. The same has to happen with a paper negative.

    Thanks for the link. Very interesting and full of tips.

    Cheers
    Last edited by goros; 06-06-2007 at 03:09 AM. Click to view previous post history. Reason: A better way to expalin it
    Alfonso

  4. #4
    Steve Smith's Avatar
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    Think about taking the picture. You are behind the camera. The paper negative is in front of you with the emulsion on the rear. You contact print emulsion to emulsion so in the final print, the emulsion is where it should be - on the front!

    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  5. #5
    goros's Avatar
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    In this case, yes. But what I had in mind was to take the picture with the paper emulsion in the front, that is on the paper side nearest to the pinhole, to make exposure time shorter and to avoid getting the paper texture on the image.

    Once, when printing a 35 mm negative, I placed by mistake the paper with the emulsion on the "wrong" side, at the bottom. The exposure time was something like two to three times nd there was a pattern on the image showing the paper inner texture. I don't mind to do that, but I would prefer to do it in the printing process (at home) rather than in the taking process (on the field).

    Cheers
    Alfonso

  6. #6
    Steve Smith's Avatar
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    That's exactly what I meant, the emulsion is facing the pinhole. Therefore, when you are viewing the scene, the emulsion on the paper negative is on the opposite side to you. When you contact print it, it reverses so is then correct.

    Do it once and you will see!

    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  7. #7
    goros's Avatar
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    Well, Steve. First of all, I'd like to thank you and everyone who is reading this thread for the time and efforts you are using to reply me. Really, I appreciate it.

    And back to business, yes, you are right. I was all the time comparing it to a 35 mm negative and making the mistake of thinking the emulsion was at the back, not at the front, of the film.

    That solves one of my questions. Thanks again.

    Regards
    Alfonso

  8. #8
    BirgerA's Avatar
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    Quote Originally Posted by goros View Post
    Hi all,

    And another one: Once the camera was built, is there any way to calculate the focal length of the hole?
    Cheers
    I think I've read somewhere that the term focal length is not entirely correct when used for pinhole cameras, but it is normally used when referring to the distance from the pinhole to the film/paper.

    Regards

    Birger A.

  9. #9
    goros's Avatar
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    Quote Originally Posted by BirgerA View Post
    I think I've read somewhere that the term focal length is not entirely correct when used for pinhole cameras, but it is normally used when referring to the distance from the pinhole to the film/paper.
    It should be that, as the focal length is the distance from the lens focal plane to the film and, in this case, the lens is just the hole.

    I asked just in case there was another esoteric way to calculate it.

    Thanks
    Alfonso

  10. #10
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    The diameter of a pinhole is critical for maximum sharpness. Perhaps the best calculator for determining this is http://www.pinhole.cz/en/pinholedesigner/ Measuring the diameter can be difficult. Needles of the correct diameter can be used as a gauge. The pinhole can be scanned and the diameter measured in a photo editor. An enlarger can magnify the pinhole for convenient measuring.

    The texture of the photo paper you observed when printing through the base varies widely with different brands. Sometimes it can be distracting. There's little advantage in using a filter with Multigrade paper.

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