henry link
Well-known member
One way to eliminate nearly all the variables except exit pupil is to make a 32mm aperture mask and place it in front of one side of your 8x42. Using one eye, switch back and forth between the two sides.
8x32 has 4 mm exit pupil;
8x42 has 5.25 mm exit pupil, that is 72% larger by area than 8x32;
8x50 has 6.25 mm exit pupil, that is 42% larger by area than 8x42.
So yes objectively the step in night sky brightness going from 8x32 to 8x42 is bigger than going from 8x42 to 8x50.
Hi Mark
I can't work out your maths. I make it
32 to 42 = 58% increase (in area)
42 to 50 = 70.5% increase
So going from 42mm to 50mm objective is more noticeable in theory than 32mm to 42mm.
I did (5.25 / 4)^2 = 1.72 and (6.25 / 5.25)^2 = 1.42. I don't know what you did, sorry.
Pies are round
Unnecessary to introduce pi.
40+2 squared is 1604+160= 1764.
32 squared is 1024.
1764 divided by 1024 is about 1723 divided by 1000, so about 72%.
Pi x Radius squared gives area so 3.14x4 for 32mm gives 12.56 and so on...
and 3.14 x 2.625 x 2.625 = 21.65
and 21.65 / 12.56 = 1.72 just like I said...
Maybe they're just very interested in one another? ...Which raises a question, does loving birds improve the performance of one's binoculars?When I look at movies with young actors, the pupils are often huge, sometimes up to 9mm.
To pick up on Binastro's point in post #30 . . .
While the standard formula to calculate the area of a circle produces an exact result, for most to use it requires a calculator of some sort
And while that’s not a big deal with the proliferation of hand held digital devices, there is a much simpler way to calculate the relative area of two or more circles
- just square the diameter
That is, eliminate Pi as it’s a constant, and don’t bother to divide the diameter before squaring it
It's a good technique for when you have to use your own embedded device
Leica uses this simplified calculation in it’s manuals for the relative area of exit pupils, where it’s called Geometric Light Value
And it works equally well to compare the relative area of objectives
John
Hi Mark
Apologies - I worked out my %age increase incorrectly.
I agree with you though I would express the increases as 172% and 142% respectively.
My head hurts....