Size of viewfinder image?

I am not at all sure why you are talking about angle of view. What does angle of view have directly to do with angular subject magnification?
You could conceivably use AOV in some intermediate math as long as you adjust for other factors,, but the fact is, you can have the same subject magnification with different angles of view. If my FF camera did crop mode by matting 61% of the sensor area instead of magnifying an extra 1.6x, the angle of view would be different, when the magnification would be the same. The optics of the viewfinder also play a role; the same angle of view with a sensor size and focal length

We have an angle of view windowed in the used sensor area (based on focal length and sensor size), and we also have an angle that the EVF appears to exist at (independent of focal length), but neither defines magnification alone without other factors.

That's how I understand "Angle of View". Tom seems to be conflating that with how large an EVF or ground glass screen appears to be as an angle, which should have another name, like "Angle of Display".

If we could digitize what our retinas actually capture, I'm sure we'd be shocked by how horrible our organic sensors and lenses are, and give due praise to our brains that make consistent simple sense out of crap "hardware". I'm certain that the reason why humans tend to lose their ability to focus at certain distances, seemingly "all at once", because the brain compensates as focus starts to fail, and then at some point can no longer make sense out of the data, so we get a perceptual threshold effect that is probably based on a more subtle and gradual loss of focus.

I find it interesting how much energy our brains waste on obsessing over focus. I've noticed that when I do puzzles like Sudoku, Ken-ken and Kakuro, if I don't have my positive diopter reading glasses, and the paper is slightly OOF, where I can see the lack of perfect focus, but still recognize numbers seemingly as fast as I would with perfect focus, my brain keeps protesting the lack of focus, and I find clues at a much lower rate, and make more mistakes. Same when I play an 8x8 game of minefield on a large monitor, but I am not focused on it. Each clue numeral is easy to see immediately, but the lack of focus just completely breaks down my ability to assimilate information. This would explain why people have such a visceral affinity towards Nearest Neighbor downsampling, and under-sampled captures with large pixels. We did not evolve to see things magnified any larger than proximity alone allows, and our lower-level lizard brain freaks out over perceptual softness in a capture.

Thanks for re-posting the above which, to me, clarifies the matter of appearance of a scene in a viewfinder:

It also covers the case of Sigma's odd-ball "SportsFinder" where what you see is not what all gets captured and also covers a Finder with frame-lines and also covers my Sigma with a viewfinder Magnifier and probably covers Diopter adjustment too.

A truly Unified Theory !! 😉

I am not really concerned about the names, along as it is understood that there are two different concepts here and I was talking about both of them. I have understood the difference for decades, it is other people here who may be conflating the two.

The angle of view of the camera when taking the picture is one thing. It is determined by the size of the sensor and the focal length of the lens.

The angle of view of the viewer when looking at the picture is an entirely different thing. It is determined by the size of the image being viewed and the distance to the viewer's eye.

It is a great pity that these things are not taught in photography books and tutorials in the way that they used to be when I started taking an interest in photography in the 1950s.

HAND.

[deleted]

You have missed the point. For a viewfinder, the angle of view remains constant, while the angular subject magnification does not (it also depends on the focal length of the camera lens). If I know the angle of view and the coverage, that tells me most of what I need to know about the viewfinder.

Personally, I find the angle of view more intuitive and easier to understand than the viewfinder magnification.

Because the angular subject magnification varies with the focal length, the viewfinder magnification is defined as the angular subject magnification for a 50mm lens. That focal length is quite arbitrary, but has probably been chosen because 50mm is commonly regarded as the "normal" focal length for full frame cameras. However, that means that the definition does not work very well across formats. An MFT camera with a viewfinder magnification of 1.0 will have only about half the angle of view of the viewfinder of a FF camera with a viewfinder magnification of 1.0.

HAND.