Relative Brightness in Binoculars?
 

Earlier I asked a question about which binos would be best in the $250 to $300 range and I got some great responses that I will go with some Pentax. But I would like to know what is meant by relative brightness it seems a 8X binocular has more than a 10X even if they are the same model with both having 42mm objective lenses. Thanks for any info.

RE: Relative Brightness in Binoculars?
 

Theoretically the lower powered binoculars will be brighter due to a larger exit pupil.If you divide the lens size by the power you arrive at the exit puil.42 divided by 8 results in 5.25 compared to 4.2 for the ten power binocular.Unfortunately theory does not always hold true in the optic world.The quality and amount of lens coatings also has a big influence on brightness.In other words a high quality 10x42 binocular could be brighter than a 8x42 binocular with lesser quality coatings.

RE: Relative Brightness in Binoculars?
 

This might help. http://www.eagleoptics.com/search.as...tness&pid=3377

RE: Relative Brightness in Binoculars?
 

Ok it must be due to the larger exit pupil. I am looking at some Pentax DCF HRII in a 10x42 with a relative brightness of 17.6 or there is a 8X42 with a brightness of 27.6. One more question. What exactly does this number refer to or mean? Since I usually hunt in more open country I think it would be best I go with the 10X so I guess you have to give a little to go one way or the other.