Thanks for the extra info. I had never considered the extra resolution
afforded by the larger diameter objectives but should have thought of
that. But even so, I don't think I could be persuaded to carry a pair
of 7x50s very far. Sort of like there's nothing photogenic more than
500 yards from the car.
Chuck Norcutt
Moose wrote:
> Chuck Norcutt wrote:
>> The first thing is to understand the size convention which is to
>> list magnification and objective lens diameter. For example, the
>> common 7x35 (and there's a reason why it's common) means
>> magnification 7X and an objective (front) lens diameter of 35mm.
>> These two numbers are important since together they determine the
>> size of the exit pupil.
>>
>
> <big snip>
>
> Nice explanation of issues I was too busy/lazy to spell out. The only
> problem is that it leaves out at least a couple of related issues.
>
> A problem with exit pupils beyond what you have said is that they
> also affect ease of use. With a small exit pupil, careful alignment
> of both optical paths and irises is required. Some people find this
> troublesome, complaining about difficulty getting them adjusted so
> the image is not partially occluded in one eye or the other.
> Particularly a problem for some with folks with glasses and some
> vision problems.
>
> The whole objective/magnification/exit pupil business interacts with
> resolution. Assuming equal optical quality and good vision, the 7x50
> in the beach example is capable of resolving more detail than the
> 7x35. Just as with camera lenses, and all optical systems, resolution
> is a function of aperture. This factor is important in birding, which
> is why you often see serious birders hauling around bigger, heavier
> binocs than might otherwise seem needed.
>
> Moose
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