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RedIrocZ-28
Pooh-Bah
Reged: 09/18/05
Posts: 1186
Loc: Grand Rapids, Michigan
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I have been reading the past week on forming mirrors, building Refractors etc. And this may be a question thats been thought of before and discarded as impossible because of this reason or that. But I'd like to ask it anyway for my own sanity.
I am sure we all know about fibre optics at least a little bit. Great transmission of light, and little if any noticible loss (due to total internal reflection). So, what would happen if you were to build a giant fibre optic tube of acrylic, shaped like an elongated cone, with a figured lens on the Objective end, and the other end of the cone cut perpendicular flat.
Would the visible light not be bent internally and come to focus at one point, i.e. the R/G/B all in focus at one point?
Like I say, maybe a very idiotic question, but just an idea. I know the weight would be obscene. And the cost to make such an object would be ridiculous.
Anyway, it would look something like this.
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4940
Loc: MA
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Look here.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3463
Loc: Doylestown, PA
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Yes it could.
The 'focal' length will depend on the curvature of the entrance surface and the refractive index of the glass (assuming air to glass interface).
This is also what really happens at the air to glass interface of any lens. In simplified optics instruction most lens are considered "thin" and the total curvature only is considered. In reality, a lens will have two air-glass interfaces, one when the light 'ray' enters the glass air -glass) and a second when the 'ray' leaves (glass-air) the glass. In your example the lens is so thick that the rays come to a focus before exiting.
The classic physics book problem uses a glass sphere or a glass rod with curved ends.
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
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RedIrocZ-28
Pooh-Bah
Reged: 09/18/05
Posts: 1186
Loc: Grand Rapids, Michigan
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So, what you guys are saying is that even though there is only 1 air to glass surface before the rays converge at the focal point (vs. 2+ air to glass or glass to glass surfaces), which would be the end (backside) of the lens it still wouldn't work?
Either way, I guess I was looking to see if it is possible to make the lens long enough that the rays would all converge while still inside the lens. And if that were the case, then would chromatic abberation, comatic abberation etc. be supressed?
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3463
Loc: Doylestown, PA
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The rays could converge before reaching the the end. Look at the link Luigi posted again.
Chromatic aberration would NOT be suppressed. The refraction angle has a wavelength dependence. See this and is what causes Chromatic aberration.
Edited by walt r (09/30/09 05:34 PM)
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hwhall
member
Reged: 09/22/08
Posts: 188
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> build a giant fibre optic tube of acrylic, shaped like an
> elongated cone, with a figured lens on the Objective end,
> and the other end of the cone cut perpendicular flat.
Seems like that is just a curious plastic lens instead of anything related to fibre optics.
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