<p>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?</p>

CC BY-SA 4.0
2023-01-13T10:22:18.487Z
A 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
CC BY-SA 4.0
2023-01-13T10:27:03.723Z
Sounds like an interesting project especially for education. But JWST doesn't have primary mirror from flat segments.
Leos Ondra
CC BY-SA 4.0
2023-01-13T10:46:51.373Z
@LeosOndra are you talking about those 18 segments, and they aren't flat????
Tapan Gupta
CC BY-SA 4.0
2023-01-13T10:55:00.207Z
@planetmaker I am not intended to make a telescope like JWST  .If it would work , i am ready to make a newtonian.
Tapan Gupta
CC BY-SA 4.0
2023-01-13T11:05:24.677Z
@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
CC BY-SA 4.0
2023-01-13T11:07:03.517Z
@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
CC BY-SA 4.0
2023-01-13T11:57:50.773Z
Oh ,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
CC BY-SA 4.0
2023-01-13T12:25:45.303Z
@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
CC BY-SA 4.0
2023-01-13T12:25:46.520Z
yes, 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
CC BY-SA 4.0
2023-01-13T12:50:32.557Z
@planetmaker ,brother, can I get your instagram id
Tapan Gupta
CC BY-SA 4.0
2023-01-13T14:38:42.943Z
@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
CC BY-SA 4.0
2023-01-13T15:04:52.480Z
@LeosOndra ye sir , i understood my mistake,  is there any other way of making a parabolic mirror
Tapan Gupta
CC BY-SA 4.0
2023-01-13T22:40:39.007Z
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!](https://astronomy.stackexchange.com/a/43850/7982) 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
<telescope><james-webb-space-telescope><cassegrain-telescope>
Can we use plain mirror as a secondary mirror in cassegrain telescope?
Tapan Gupta
# Can we use plain mirror as a secondary mirror in cassegrain telescope?

(Asked by: username_0 on 2023-01-13)

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?

**Tags:** telescope, james-webb-space-telescope, cassegrain-telescope

> **Comments:**
> **username_1**: A 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  
> **username_2**: Sounds like an interesting project especially for education. But JWST doesn't have primary mirror from flat segments.  
> **username_0**: @username_2 are you talking about those 18 segments, and they aren't flat????  
> **username_0**: @username_1 I am not intended to make a telescope like JWST  .If it would work , i am ready to make a newtonian.  
> **username_2**: @username_0 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.  
> **username_1**: @username_0 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.  
> **username_0**: Oh ,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  
> **username_0**: @username_1 or@username_2 ,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  
> **username_1**: yes, 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).  
> **username_0**: @username_1 ,brother, can I get your instagram id  
> **username_2**: @username_0 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).  
> **username_0**: @username_2 ye sir , i understood my mistake,  is there any other way of making a parabolic mirror  
> **username_3**: 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!](https://astronomy.stackexchange.com/a/43850/7982) 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  

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## 0 answers

