A larger objective will always be brighter but I understand it's not a certainty you can use it - but it's brighter, period.
If you cannot use the entire light, the larger exit pupil size will mean the device will have larger eye relief and just be easier to use all around.
10x50 is brighter and easier to use than say 10x42 and especially 10x30.
So, more exactly, HOW is the larger objective brighter? Beats me when I try to understand your assertion.
Are you not admitting that there are occasions when the user cannot use all the light that comes through the exit pupil?
While optical brightness of binoculars is determined by the exit pupil size, by squaring it, the user position is the guiding principle for how to gradate brightness for that individual user
and at the momentary level of illumination.
The technical brightness value does not tell the final truth about how bright the binoculars will appear. It does tell that they have the possibility to deliver more light to the eye, not that they will always appear brighter.
There was a recent discussion where there were claims that binoculars with too large objectives/too large exit pupils would actually be less bright than those with objective sizes that match the user's pupil.
Exactly the opposite to what you claim.
That is incorrect, just like your idea that big objective binoculars will always be brighter (if that's what you're saying)
I maintain it's only brighter compared to a smaller exit pupil binocular when at least the smaller exit pupil is smaller than the user's pupil.
If both are smaller than the user's pupil, the larger exit pupil will be the brighter anyway.
And no, eye relief has exactly nothing to do with this.
It's just optics / science 101.
We are not talking about different coatings or pupil size. Two equivalent devices - one with 42mm and the other with 50mm - the latter will gather more light. It's just optics / science 101.
Leica 7x50 will be brighter than same model in 7x42.
I've compared 42mm optics with 30mm optics - the former are noticeably brighter. You cannot get any 30mm optic to show up as bright as a 42mm, nor can you get a 42mm to show up as bright as a 56mm. Same brand, same configuration.
if you have issues seeing it, then that is another problem. It is a user problem at that point.
The larger the pupil exit size, the brighter it appears and the easier to use.
Brightness is determined by exit pupil size and more is better. You get bigger exit pupil size by keeping the same power and going to a larger objective. Or something like a 6x42 device - not sure if anyone even makes that.
In a 7x50 configuration, if your eyes cannot make full use of the 7mm exit pupil, then it's a user issue. But 7x50 is scientifically brighter than say 10x42. If this applies to you, 8x42 might be just as effective as 10x56.
here is a post articulating this well:
https://www.birdforum.net/showpost.php?p=1563082&postcount=3
Now, if I look at a huge wall with uniform colour and brightness, and then I take a swimming ring and look through it, the wall's brightness won't be any different. And going from the swimming ring, via a napkin ring to a 10 mm hole in a black sheet of paper, nothing will change the perceived brightness of the wall. Same brightness - no more, no less.
But as soon as the hole is smaller than your own pupil, the perceived brightness will decrease because the exit pupil now substitutes your pupil as the limiting aperture of your eye's optical system.
It is not the objective size that determines the perceived brightness, it is the exit pupil size, but the perceived brightness will not decrease until the exit pupil is smaller than your own pupil.
In reality, this means that if your pupil is restricted to an absolute maximum of 3 mm, a 10x30 will for you always be as bright as a 10x70.
One could admit that the bigger exit pupil "scientifically" is brighter than the smaller one, but that line of thinking violates the very concept of how binoculars are used. If you're totally blind and cannot even perceive light, the notion of a "brighter" binocular, or for that matter one with more magnification, is useless.
Binoculars' usefulness is inseparably associated with the human vision, and not one of their optical properties have any meaning without the user.
So using the phrase "user issues", "user problems" as if those were rare exceptions, and claiming the greater geometrical brightness to be almost always noticeable and useful, is misleading.
//L