determining "loupe" magnification

Discussion in 'Darkroom Equipment' started by pellicle, Sep 29, 2008.

  1. pellicle

    pellicle Member

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    Hi

    I have an old "loupe" type magnifier here but it has nothing written on it which would give me an idea as to its magnification.

    Can anyone suggest a way for me to 'estimate' how many x (times magnification) it is?

    thanks
     
  2. Struan Gray

    Struan Gray Member

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    1. Estimate the focal length by seeing how far from a piece of paper the glass of the loupe has to be to focus a distant scene such as a tree some tens of meters away.

    2. Magnification = 1 + (250mm/focal length)
     
  3. Pinholemaster

    Pinholemaster Member

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    If your friends have loupes of different magnifications, compare yours to theirs.

    There are not that many variations. 4x, 6x, 8x, 10x, etc.
     
  4. OP
    OP
    pellicle

    pellicle Member

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    Hi

    I assume you want focal length in mm ... so focal length in is ~45mm plugging this in would be:

    1 + (250 / 45) = 6.5


    ok ... thanks :smile:
     
  5. OP
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    pellicle

    pellicle Member

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    Hi

    I wish I had any friends that were into traditional photography. Here in Finland people are digital or not into it. (lets see if that starts anything ... :confused:smile:
     
  6. Struan Gray

    Struan Gray Member

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    Sorry. Should have said so, but you got it right so no harm done.

    FWIW, the 250 mm is a figure for the closest focus of a mythical average person's eyes. If you can focus closer that that, the magnification - for you - increases proportionally.

    FWIW (2) this definition assumes that your eye is close to the loupe. If you back off and and use the loupe like a reading magnifier you lose the one from the formula - i.e. your lens would be a 5.5x magnifier.


    Struan