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Thread: Human sized camera

  1. #21
    Tin Can's Avatar
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    Dec 2011
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    Re: Human sized camera

    [QUOTE=Jim Jones;1550912]
    Quote Originally Posted by Pere Casals View Post

    . . . Of course it will work, your aperture will be small so exposure will be long. With pinhole you have the blurr confusion circle around the hole size, suposing subjet is far, a larger blurr circle if subject is close.

    For a 1200mm focal you are to use a 1.5mm hole delivering f/822 . Here it balances optimal diffraction vs hole : https://www.mrpinhole.com/holesize.php

    Your image would have a 1.5mm blurr circle.

    Pros: you only need a hole, a 1.5 mm one it's easy to make. Holes for smaller formats have to be better machined to do a good job.

    Cons: low speed, 1.5mm blur for f= 1200. . . .

    There are many recommendations for the correct diameter of any focal length in pinhole photography, often based more on theory or poor advice rather than on hands-on experience. Based on my experience, the optimum pinhole diameter for a 1200mm focal length would be about 1.3mm. This would resolve about 1 line pair/mm where the on-axis blur circle from geometric optics and diffraction phenomena are about equal. At that point, image blur is less than predicted by both geometry and diffraction. As the pinhole diameter increases, geometry determines image blur. As the pinhole diameter becomes smaller, image blur increases in a less predictable manner due to diffraction. Also, interpreting image blur of standard test charts varies among different people.

    Wide angle pinhole photography brings up other factors which affect one's choice of pinhole diameter. As the angle of coverage increases, some photographers may wish to slightly increase the pinhole diameter to improve sharpness towards the edges of the image despite enlarging the central image blur. A pinhole image has negligible drop-off in sharpness up to 20 degrees from the pinhole axis. By 40 degrees there is little loss In radial sharpness, but about 35% in tangential sharpness. By 50 degrees the radial sharpness has dropped of noticeably and the tangential sharpness by 60%. This demonstrates that wide angle pinhole cameras show substantial astigmatism in addition to the distortion that all wide angle cameras have. If we move in close with a well-designed wide angle pinhole camera while maintaining the same image size, the image blur decrease. That is one way of improving pinhole image sharpness if the subject permits.

    Much of this information is based on 40-year-old photography. It is based on rather casual photography instead of the more rigorous work that would be more valuable to researchers. I don't even have a darkroom now. If the more inventive photographers on this site unite to pool their findings, we may become the new center for pinhole photography.
    Very good info and new to me

    Thank you
    sin eater

  2. #22

    Join Date
    Jul 2016
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    4,498

    Re: Human sized camera

    [QUOTE=Jim Jones;1550912]
    Quote Originally Posted by Pere Casals View Post
    Based on my experience, the optimum pinhole diameter for a 1200mm focal length would be about 1.3mm. This would resolve about 1 line pair/mm where the on-axis blur circle from geometric optics and diffraction phenomena are about equal. At that point, image blur is less than predicted by both geometry and diffraction.
    Jim, clearly the geometric blur circle is uniform and exactly equal to the the pin size for distant subjects, when taken rays are parallel (distant subject) the pin circle is exactly equal to the projected circle...

    Click image for larger version. 

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    (hole painted way larger than ideal to show the effect)

    but the blurr effect in the resolving power is lower, because when adding all circles generated by a white line (say vertical lines patern) adds more overlaping light power in the vertical direction than in the horizontal direction.

    I guess this may explain the difference between blur circle size and the better than expected resolving power...

    I guess that the ideal hole depends also in how well made it is, what subject distance optimized, what (angle) format size vs focal length...

    If your ideal circle is 1.3mm instead what the calculator says... then of course your hole is of high quality, generating a lower diffraction from a perfectly smooth bore.


    For the moment my experience is only with paper negatives, mostly at around 240mm focal for 5x7, but I plan to play with larger formats. Clearly the larger the hole the easier to make an efficient one !!

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