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  1. #1

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    Interchangeable lens camera when aperture size remains constant!

    So I tgot tis Diana F+. Loving it and all my expsoures seem to be spot on for all the settings, given I was using an ISO 400 film (I believe the shutter speed is around 1/60-1/100s) and the apertures on the camera are as follows": Cloudy - f11, Partially Cloudey - f13, Sunny f-19 and a Pinhole setting of f150.

    Now here is my slightly technical question (I know bizzare to say that about a Toy Camera)...

    All the above f numbers are for a lens on the camera of 75mm. On the Diana F+ you can change the lens (e.g. to a 38mm lens) while the Aperture remains a part of the body. Given the focal length has changed, and the aperture diameter has stayed the same for the various settings...does that mean the f number has changed?

    i.e. I now has a 38mm f5.6, f6.8, f9.6 for the same settings? (Using the f numbers claimed by the Lomography group, I have calculated the aperture diameters to be 6.8mm, 5.7mm and 4mm)

    I know this may seem like overthinking it, but I have a project coming up with the camera, and I would rather not come back with massively over-exposed negs (in this case possibley up to 2 stops!!).

    Rgds, Kal
    Kal Khogali

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  2. #2
    Christopher Walrath's Avatar
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    The aperture value is a ratio between focal length and aperture diameter. A 75mm lens with a body aperture value of f/11 has an aperture diameter of just under 7mm (75/11=6.81). That same aperture (part of a camera body and not the lens) with a 38mm lens would give an aperture value of about f/5.6 (5.6*7=39.2). If the aperture is part of the lens then the aperture value would remain the value published on the lens.
    Thank you.
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  3. #3

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    That's what I was thinking, but that is not referred to anywhere on the web...i.e. that as you change lens on the Diana so the f number changes....two stops is a massive amount Toy camera or not....thanks for confirming my view. Rgds, Kal
    Kal Khogali

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  4. #4

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    One VERY easy way to find out for sure: Take a pic with the attachment off. Then take the same pic with it on. Finish the roll any way you like and process. Compare the negatives.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

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  5. #5

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    Thanks 2F...I have switched lenses half way through the test roll and will take a couple of shots at various settings just to be sure. Rgds, Kal
    Kal Khogali

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    "Wake up, dream, and photograph what you have seen.
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  6. #6
    ic-racer's Avatar
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    If you have a way to check the size of the entrance pupil as viewed from the front of the lens at the various settings (like a "B" setting), you can calculate the F numbers from there.

  7. #7

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    That is what I have done ic-racer..as per the measurement above which is consistent with what I see with my eyes. Need to remember that when using the 38mm, ISO100 film will be better for most uses. K
    Kal Khogali

    www.kal-khogali.com


    Visit my Photo Scrap Book

    www.shutteringeye.wordpress.com


    "Wake up, dream, and photograph what you have seen.
    Don't wake up, photograph, and dream of what could have been."



 

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