Members: 77,698   Posts: 1,716,086   Online: 982

1. ## determining "loupe" magnification

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

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

4. Hi

Originally Posted by Struan Gray
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)
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. Hi

Originally Posted by Pinholemaster
If your friends have loupes of different magnifications, compare yours to theirs.

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

6. Originally Posted by pellicle
I assume you want focal length in mm ...
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

 APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY: