Quote:
Originally Posted by JA
As per Erwin and Ray's comments on the field of view (acceptance angle, solid angle of view or however named), it is like considering a ray diagram for a convex lens with an object at infinity with on-axis parallel light rays(BLUE) and off-axis parallel (GREEN and RED) rays from infinity. The field of view being formed by the angle between the GREEN and RED rays as shown.
This is shown in the attached ray diagram, with the 3D effect forming a cone, or more correctly a truncated cone at the lens surface.
Best
JA
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Great diagram. Certainly helps toward visualising an optic's field of view.
Then I pondered the "magnifying glass" concept for a bit...it was sort of a Eureka moment for me
...and considered the flux being converged by an optic.
With a BIG magnifying glass, and a sunny day, you can burn most things
with a concentrated image of the sun.
But a (very) long focal length lens gives you a nice big solar image, but no smoke.
Similarly, a tiny short focal length lens gives you a tiny bright spot, but again no smoke.
The simple physics is not enough concentrated flux in either case.
But this only applies to extended sources (eg Sun/Moon/Nebulae) that you can concentrate.
With point sources..eg stars.... aperture wins every time.