Re: Binocular help. 700 dollar budget
Originally Posted by
Elkaddict
Agreed, years ago I had some first gen Pentax DCF 10X42s. My buddy liked them so much he got some 8X42s. We compared them side by side, real world, out in the bush. Wider field of view and brighter view in really low light trumped the very little gain in image size.
- The diameter of the objective lens (furthest from the eye) basically determines how much light the binocular gathers. Hence, larger objective lens more light gathered.
- In low light conditions, our eye pupils can open up to 7mm. Suppose that Elkaddict's binos had an exit diameter of 7mm while his buddy's were very large at 19mm, then of course the light is going to be brighter in the lower power binos . The same reasoning applies in ToddBartell's example where he states that the exit lens was larger. Take the 10x and the 8X with the same diameter objective and exit lens and they will be closely comparable except for the magnification.
- Then there is "relative brightness" which is actually a scale pertaining to the exit lens. If you take an exit lens with a 4.5mm diameter and square that number, the result is 20.25 indicating a level of brightness. With a exit lens diameter of 7, the square is 49 which is more than double the brightness of the 4.5mm. Then there is the 18mm exit lens which when squared is a whopping 324. Project these numbers on a straight line and you can see the difference of light you can see.
- Essentially, you should pick a set of binos with an exit lens diameter of at least 7mm. Of course, light gathering is enhanced with an increasing objective lens diameter but unless you are star gazing, it would be best to restrict that to less than 50mm. If you are hunting dense forest, then you would prefer low power binoculars, something in the 6 or 7 power range to take advantage of the wider FOV.
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