Wikipedia in the article about refracting telescopes says “The combination of an objective lens and some type of eyepiece is used to gather more light than the human eye is able to collect on its own, focus it, and present the viewer with a brighter, clearer, and magnified virtual image.”
I found a page which uses this terminology: surface brightness (which would be amount of light per unit of solid angle) and “total brightness” (which would be total amount of light received by the eye and what I would call “brightness” whithout qualification).
Since telescopes are often used to view stars, and since stars are point-like, saying the image is brighter doesn’t contradict what people in this thread are saying.
I, and I suspect most people, would use “brightness” without qualification to mean surface brightness, not total brightness.
Wikipedia uses “brighter” without qualification to mean total brightness, not surface brightness.
Furthermore, if brightness without qualification is understood to mean surface brightness then:
The question “which star is brighter?” is meaningless
The question “which planet is brighter” cannot be answered just by observation and requires calculation regarding total light observed and surface of the disk of the planet.
Your quote says precisely what I’ve been trying to explain.
My point being, without altering the projected angular size smaller than what the naked eye percieves, you can’t make the image brighter with optics alone.
A 1:1 projection will yield you nothing insofar as amplifying brightness, however you define it (indeed, since you’re using imperfect lenses or mirrors, you’d actually be degrading the image if ever so slightly below human perception). Whether you’re projecting this image on a wall or your retina makes no difference.
Again, we are in the field of semantics in this thread.
I would propose that brighter / dimmer refer to total or absolute brightness and darker / lighter would refer to “surface brightness” or “relative brightness” by area unit.
I do not think your explanations are helping clarify anything. I think from the very beginning we are all here in agreement about the concepts and what is being discussed is the terminology.
The way I interpret it at face value I would say it is wrong. Then you explain that you mean something else which is in agreement with what I think and what the other web sites say. Then I say I agree with the concept as explained but not with the way it was initially expressed. Yeah, I would say that is semantics. Or are we now going to argue about what is and what is not semantics?
I agree it cannot be done with a simple, two lens, objective-eyepiece, telescope or binocular.
I have no idea if it can be done or not with more complex lens combinations. I have seen plenty of camera lenses which were complex enough that I did not understand them. Some had effective focal lengths which were in front or behind the actual lenses which I did not quite understand at the time I saw them.
So, while I agree a simple, two piece telescope magnifies brightness in the same proportion that it magnifies area (neglecting losses in the glass), I do not know if this is true for all complex lenses and it has not been shown or proven here.
I certainly have never seen such a device that would provide brightness amplification but not size magnification. This does not prove it is conceptually impossible to design and built though.
There is nothing to test with camera lenses. The light-gathering ability of a camera lens is measured by the f number which is a direct function of the diameter of the lens and its focal length.
I have never seen it done and this I consider a strong indication that it is probably not possible. But it doesn’t prove it.
Sailing directly into the wind seemed impossible until it was done.
I have not seen proof that a large diameter lens system cannot gather light and concentrate it so it can go into the eye. I understand this cannot be done with a simple two lens telescope because this system just effectively lengthens the eye’s focal length so what you gain one way you lose the other. But I have not seen proof that it is impossible to do with more complex lens systems.
“So you’re telling me, that with this lens system, I can use a standard, consumer 100w lightbulb to project film, shot in IMAX, and it’ll project this image at 580x while also amplifying the light as it diffuses across the theater, as if I were using a 15 Kw lamp?! I’ll take all you have!”
