beseler lens

[v1d9uy]

i found a beseler lens says its a 135mm 1:5.6 enlarging lens
but says nothing about FOV i have no idea what the 1:5.6 means
im no optical expert.

[dnsey]

1:5.6 means that the aperture is f/5.6.
To estimate the FOV, take the lens outside, and hold it to focus a view of the surroundings onto a sheet of paper. You'll see quite easily where the brightness drops off. Allow 10-15% smaller radius for practical use (to compensate for the eye's poor ability to judge such things).

[v1d9uy]

my problem is i dont have it ... but i can get it for $30

[dnsey]

It's impossible to tell what the FOV will be without further information.
A serial number might enable you to track down the design, or if you know the original application that will give you a good clue.
If I had to guess, I'd say that an 'enlarging lens' of that FL was either for a medium-format enlarger (6 X 9 cm?), or a process camera (W/A lens for A3+ format).

[Guy Grotke]

These are generally too small in diameter to use, unless you have a short-arc lamp. If you really need a 135 mm lens (for a tiny LCD?), then I would look at surplusshed.com. But I have no idea where you would find fresnels to match that short a focal length.