I was planning of making a telescope like JWST, just with plain mirrors, as bigger concave or convex are much expensive. The primary mirror would be totally made of plain mirrors configured like JWST. I'm having doubt regarding secondary mirror: can i use plain there?
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planetmaker
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Tapan Gupta
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2A plain secondary mirror serves no optical purpose other than changing the direction of the light. That alone means you hence will not build a telescope like the JWST, but a segmented Newtonian telescope. Probably you rather build a kaleidoscope than a telescope that way with only flat mirrors – planetmaker Jan 13 '23 at 10:22
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2Sounds like an interesting project especially for education. But JWST doesn't have primary mirror from flat segments. – Leos Ondra Jan 13 '23 at 10:27
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1@LeosOndra are you talking about those 18 segments, and they aren't flat???? – Tapan Gupta Jan 13 '23 at 10:46
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1@planetmaker I am not intended to make a telescope like JWST .If it would work , i am ready to make a newtonian. – Tapan Gupta Jan 13 '23 at 10:55
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1@TapanGupta Exactly. They are not flat. They are slightly and precisely curved. I believe that they together form a part of ellipsoid surface. If you want to make a primary mirror from a flat pieces they must be very small otherwise you get a blurred image. – Leos Ondra Jan 13 '23 at 11:05
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1@TapanGupta No, the segments of the JWST are not flat - they form all together a perfectly curved surface. The optical principle is that: https://en.wikipedia.org/wiki/Three-mirror_anastigmat - the segmenation's purpose is to reduce the weight needed for the complete optics and to make manufacturing easier.itself and the structural support can be made much lighter - and to allow folding so that it fits onto one of the rockets. – planetmaker Jan 13 '23 at 11:07
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2Oh ,actually when i searched this on google it shows that the mirror segment is 1.3 meters FLAT TO FLAT i thought they are talking about the curve , but i think they were showing the flat to flat length of the segment – Tapan Gupta Jan 13 '23 at 11:57
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1@planetmaker or@LeosOndra ,isn't there any other way to make a effective telescope out of plain mirrors, actually ready-made telescope aren't affordable here in india – Tapan Gupta Jan 13 '23 at 12:25
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1yes, they are talking about the diameter of each segment there, measured from one flat border to the opposing flat border (and not edge to opposing edge as one could also measure). – planetmaker Jan 13 '23 at 12:25
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1@planetmaker ,brother, can I get your instagram id – Tapan Gupta Jan 13 '23 at 12:50
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1@TapanGupta If you need only to collect light (solár furnace) then you can use flat mirrors. If you want to create image you need curved mirrors (or lenses). – Leos Ondra Jan 13 '23 at 14:38
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1@LeosOndra ye sir , i understood my mistake, is there any other way of making a parabolic mirror – Tapan Gupta Jan 13 '23 at 15:04
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For my first telescope I used a small front-surface mirror, some alligator clips, an eyepiece from an old pair of binoculars, a cardboard tube (a la Clyde Tombaugh) and a weak concave magnifying mirror for my first 10 cm Herschellian reflector telescope and had a truly thrilling time! The hard parts about making a telescope "like JWST" include not only that both mirrors have specific curves, but that the primary has a big hole in it! I think you should stick to trying to make a Newtonian or Herschellian if you are using a household mirror – uhoh Jan 13 '23 at 22:40