aperture and magnification gain puzzle


Let's use this aperture 50mm and 70mm for refractor...

50^2= 2500
70^2= 4900

So 70mm has almost twice the area of the 50mm...

Now let me use 10mm eyepiece....

both refractor is f/8. Therefore 400mm/10=40X and
560mm/10=56X.

The 50mm has 40X, the 70mm has 56X both having the
same exit pupil of 1.25mm...

Now my question is...

The 70mm is supposed to have twice the area of 50mm...
so it should be twice as bright... however they have
the same exit pupils at 40X for the 50mm objective
lens and 56X for the 70mm objective lens. Where did
the extra twice brightness of the 70mm go?? There is
only small increase from 40X to 56X. Since both
have same exil pupils of 1.25mm, hence same brightness
at the eyepiece. What happened to the twice brightness
of the 70mm?? If its 80X versus 40X, you can put it in
the same difference, but at 40X and 56X?? Do you mean
the twice brightness is used up at 56X (in the 70mm)
versus the 40X (in the 50mm lens)??

Ch.

.

Relevant Pages

  • Re: aperture and magnification gain puzzle
    ... > same exit pupil of 1.25mm... ... > The 70mm is supposed to have twice the area of 50mm... ... > lens and 56X for the 70mm objective lens. ... What happened to the twice brightness ...
    (sci.astro.amateur)
  • Re: aperture and magnification gain puzzle
    ... >> same exit pupil of 1.25mm... ... >> so it should be twice as bright... ... >> have same exil pupils of 1.25mm, hence same brightness ... compared to 26.6X magnification. ...
    (sci.astro.amateur)