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Re: How does the AstraIIIb split mirror work?
From: Ken Muldrew
Date: 2004 Apr 25, 16:59 -0600
From: Ken Muldrew
Date: 2004 Apr 25, 16:59 -0600
Trevor J. Kenchington wrote: > Ken, > > I suggest you check the geometry again: > > Let the angle of incidence of a ray of light onto the front of a piece > of parallel-sided glass be A. The reflected ray will then leave the > glass also with angle A but on the opposite side of a line drawn > normal to the plane of the glass. > > The refracted ray will pass into the glass with an angle from the > normal of B, such that sineA/sineB is equal to the refractive index of > the glass. That ray will then be (in part) reflected from the back > side of the glass with angles of incidence of B (the glass being > parallel-sided). > > On returning to the front side of the glass, the light will still have > an angle of incidence of B and will be refracted again such that > sineA/sineB is equal to the refractive index. Thus, it will leave the > glass at an angle A from the normal, just as the ray reflected off the > front of the glass was. Whoops! It looks like I was reversing my second refraction. The light rays coming out of both sides should be parallel, and as George says, they should focus to a point when put through a lens. I just can't understand why I was seeing double images of Jupiter last night. I understand my confusion with front-surface mirrors in telescopes now. The objective lens, or primary mirror, has put the initially parallel rays of light off-parallel, so in this case, it is like the double image that one gets from glass for nearby objects. For objects at infinity, there should be no double image from a piece of glass. I'm convinced of that, but I have to find where the extra reflection was coming from last night. I am terribly confused over this. Ken Muldrew.