Objective diameter and field of view?

[justinp61]

This may be apples to oranges but I'm curious to see. I just bought a pair of Vortex Diamondback 8 X 42 binoculars. While deer hunting last weekend I set the magnification of my Leupold 4.5-14 X 40 VX-3 rifle scope to 8X to compare the clarity to the binoculars. What I noticed the most was how much difference there was in the field of view. Even with one eye closed the binoculars had a huge field of view compared to the rifle scope.

Is this a function of the design or objective diameter?

Thanks, Justin

BTW, if Vortex scopes are as clear as these binoculars I'll be selling some Leupolds and replacing them with Vortex.

 

[dstoenner]

No. Objective diameter divided by magnification definitions exit pupel but width of field is in the design of the eyepiece

 

[Bart B.]

width of field is in the design of the eyepiece

Then why, decades ago, did my Weaver K3 have a smaller field of view than a K1, both with identical eye piece lenses and same diameter objective lenses?

The objective and erector lens' focal lengths and spacing forward of the eyepiece lens determines field of view at the second image plane the eyepiece is focused on. This is done to keep eye relief the same.

 

[Ledd Slinger]

Objective and ocular diameters have nothing to do with field of view. Bigger objectives just bring in more light. FOV has more to do with the distance of the lenses in the optic, which of course includes eyepiece design. Other factors involved too, but just have a read in the below link if you are really concerned about it.

https://www.edmundoptics.com/resour...understanding-focal-length-and-field-of-view/

 

[Bart B.]

Cant compare binoculars to rifle scopes, can't compare at different magnificaton levels, and can't just look at objective and ocular lens sizes. There's a lot more going on internally to set the FOV that you can't see.

use this link to a calculator to get field of view in degrees of angle.

https://astronomy.tools/calculators/field_of_view_calculations

You need to know the eyepiece field of view angle. Use a 60 degree FOV angle with different scope/binocular focal lengths.

A rifle scope eyepiece focal length is typically about 50 millimeters. The scopes objective lens system (objective plus erector/zoom lens) has a focal length 10 times that of the eyepiece if magnification is 10X.

Binocular eyepiece are about 20 to 25mm. A 7x50 binocular's eyepiece's focal length of 20 mm require the objective lens system to have a focal length of 140 mm,

The focal length of the eyepiece is the f number times exit pupil. For example, a Bushnell Custom 7x50 measured at f/3.6 with a 25mm eyepiece (7 x 3.6 = 25). The objective lens system focal length is 7 times that of that of the eyepiece, 7 times 25 = 175 mm or about 7 inches but its physical length will be different.

This link gets into more detail:

https://www.cloudynights.com/topic/13186-focal-length-in-binoculars/

 

[Bart B.]

Other factors involved too, but just have a read in the below link if you are really concerned about it.

I like your link better than mine.

 

[justinp61]

Thanks for the education guys.