Wow, Thank you to all who contributed to this thread!
I got more about the history, and a way more "confusing" ;-) answer than I ever expected!
Okay, Just for fun, Here's a twist...
With the OP conditions of a full frame, DSLR, at prime focus of a 2800mm scope, and adding here that it's a 21mp camera
For my "twist" I'm going to agree with the "Standard" of 1x for full frame camera is 50mm. Just because, as a norm, a 500mm lens bought for such a camera is almost always called a 10x lens.
So therefore my 2800mm C11Edge is a 56x lens
But any of us who've taken deep sky images with aforementioned setup, would agree that seems low for a "magnification" number.
So here's my twist to correct that....
Hi resolution images are often considered to be 300dpi, - right?
Or in our digital world, 300px/in (ppi)
Normally you print things out on standard 8.5x11 paper, with the image (with a border) say....11x7.4 (maintaining aspect ratio)
BUT the image of a 21mp camera printed on paper big enough to hold a 300ppi image would give you (roughly) an 18.7x12.5 image
Or, roughly 2.85x bigger than fitting the whole image on a standard sheet of paper.
SO FINALLY, by my convoluted reasoning, I'm going to take my 56x "lens" and multiply it by 2.85 = 160x as my hi rez magnification
And that folks is what I'm going say is a reasonable number for this setup's magnification
And I'm not going to argue about it! ;-)
To each his own I say, eh?
Edited by Ettu, 04 September 2019 - 08:02 PM.