Originally Posted by
TreednNC
Ive tried searching here and google as well, but after wading through several threads, I just can't find what I am looking for. Looking at what point is the objective size vs tube size and all a mute point in terms of low light transmission.
I know good quality glass is key here, but glass being equal, when is objective size not matter in terms of tube size and how much light the eye can take in?
The objective diameter is directly coorelated with the resolution of an object. Hense the reason a guy with a 25X20mm binocs might not be able to count the tines of a deer at 500yards, but a person with a 8X50mm might.
Also, Twilight performance factor is directly coorelated with objective and magnification. Its the square root of the two multiplied.
Brightness however is mostly exit pupil, The most a human can handle (most, depends on someone's eye) is 7mm exit pupil. Exit pupil
Exit pupil = Objective Diameter / Magnification = Eyepiece Focal Length / Objective f/number
All has to be taken into account.
Now, this is for an (ideal) lens. There is no such thing. So we have coating that is bacially thin film filters to attenuate some wavelengths, and let some thru, that the human eye is more responsive too. Human eye cannot see IR, or UV, but at the edge of night, different wavelengths are emited and more responsive to the human eye.
There are lots too it. I don't design thin films for the human eye but for an electronic eye or photonic reciever. There is a complete science for it. We used to make in house the filters. We had a 20million setup for it. It was cool. But now just like everything else, our company in its wisdom sold the equipment for pennys on the dollar and has outsourced it to China. I crap you not. Sad state of affairs.
To answer your question, the general tube size does nothing for light transmission. The coatings and objective size does. And it does this in a beautiful harmony of exit pupil along and focal lengths.