Originally posted by JS357
Typical opera glasses are 3x by 25 mm.
Did you see the ones he posted, clearly marked 30X60 which I assume means 30 mm lens and 60 power, which of course means a very narrow view, smaller than iris size.
Usually the numbers are reversed, 60X30 and clearly those glasses are not 60 mm diameter so they were probably made in China or some such country not knowing the conventions for such.
The standard hunters/birdchaser binocs are 7X50, 7 power, 50 mm lens.
That results in a view angle that matches the size of the average iris so you get a fairly wide viewpoint angle. If you had a 50 mm lens with say ten times the magnification or a 70X50, the image would be like looking through a knothole.
So to get full iris spanning image at 70 power you would need a 70X500 mm lens, a bit impractical, eh. 18 inch lens, you would have a bit of a problem just picking it up, and then you would have two of them side by side which would present its own set of problems like needing extra high quality surface reflector mirrors to go from lenses over a meter wide to the distance between human eyes. Then if you wanted 700 power........