In several different binocular reviews, people mention that the depth of field is "very good" on a particular pair of binoculars. My understanding is that depth of field is determined by:
- Subject Distance
- Magnification
- Focal Ratio of the Objective
Is there really a significant difference between brands and models? Obviously, the magnification will make a difference and the size of the objective as well (since large objective bins usually have faster focal ratios), but once you have chosen, say, 8x42 bins, are the differences in depth of field noticeable?
From comparing measurements on various Zeiss, Leica, Nikon, and Swaro roof prisms, it appears that they all have a focal ratio of somewhere between f/4 and f/5.5 with the Zeiss at the short end (presumably to keep overall length down with the Abbe König prisms which have a less "compact" light path) and the Swaros at the long end. These are only estimates since none of the manufacturers appear to publish focal ratios.
I am curious whether anyone on this forum has every really A-B'd depth of field between brands, and whether the differences are significant.
Thanks - Jared
Greetings!
I've personally found that the only factor that seemingly contributes to depth of field is the magnification of the binoculars. If there are DOF differences between brands or models that are due to some other factor besides power rating, it seems to be a minor effect at best - maybe a few percentage points.
I would love to hear otherwise if other people have actually measured this in a controlled setting... I'm going from pure observational experience on this one!
Best wishes,
Bawko
I agree with Bawko. Even objective focal ratio makes no difference. There is one special circumstance that produces a real increase in Dof and that is when the exit pupil of a binocular is smaller than the entrance pupil of the eye. You can demonstrate that to yourself by making a pin hole stop down and placing it in front of any binocular. You will see huge Dof (and a very dim image). A number of things can simulate differences in Dof, like focus speed and field curvature, but I have become convinced that magnification is the only significant factor when it comes to real differences. I came to this view the hard way, by argueing against it and then performing an experiment that forced me to change my mind. Unfortunately, I believe an earlier thread on the subject here got lost in last winter's computer crash, but there is an excellent thread from Cloudy Nights here: http://www.cloudynights.com/ubbthre...5/o/all/fpart/1