# determining "loupe" magnification

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

1. ### pellicleMember

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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 GrayMember

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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. ### PinholemasterMember

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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. ### pellicleMember

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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

5. ### pellicleMember

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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

6. ### Struan GrayMember

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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