Focal length of bins

[bomberbaz]

Ok so really not sure if this is right but here was my calculation as there isn't a focal length on Bressers website for my bins.

They are 16x42 which gives a 2.6 exit pupil. 

Devide objective by exit pupil gives F ratio 16\2.6=6.1.

Is this correct or am I barking up a wrong un?

[Peter Drew]

Sounds about right to me considering the magnification.  Common 10x50's are usually F4 - F4.5.      🙂

[BinocularSky]

On 04/04/2023 at 21:23, bomberbaz said:

Ok so really not sure if this is right but here was my calculation as there isn't a focal length on Bressers website for my bins.

They are 16x42 which gives a 2.6 exit pupil. 

Devide objective by exit pupil gives F ratio 16\2.6=6.1.

Is this correct or am I barking up a wrong un?

You're dividing the magnification, not the objective, by the exit pupil (dividing objective by exit pupil gives you the magnification). Unless I'm missing something, to get the focal ratio, you need the focal length of the objective. If you know the focal length of an eyepiece, you can work it out from that (multiply by magnification).  If you're interested, there's a CN post on it:  https://www.cloudynights.com/topic/13186-focal-length-in-binoculars/#entry157926