Questions tagged [mirror]

Questions regarding the use of a reflective surface, for example in optics.

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Why are telescope mirrors made of glass?

Optical telescope mirrors are typically made from endlessly polished glass surfaces that have been aluminised to provide a very smooth surface of reflective aluminium. But why the need for glass at ...
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8 votes
3 answers
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When did "resilvering" large telescope mirrors actually refer to aluminization, and why was it necessary?

This answer nicely summarizes the general picture of historical use of silver for mid to large size telescope mirrors, and the shift to aluminum once good quality vacuum pumps and chambers suitable ...
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8 votes
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Why telescope mirror glass shipped as randomly broken chunks of a constant size in cardboard boxes?

The video MIRROR LAB: Preparing for Casting GMT's Mirror 6 shows the unpacking several hundred boxes full of broken glass from OHARA, packed in styrofoam. The glass chunks are a fairly uniform size of ...
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6 votes
2 answers
138 views

JWST mirrors each can be "positioned in tip, tilt, piston, horizontal & vertical decentering and clocking". What does this mean?

This interesting paper by Robert Warden refers to each mirror segment on JWST as having six actuators providing six degrees of freedom in positioning (plus one more to tweak the curvature). These ...
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6 votes
1 answer
656 views

Do primary mirrors in large observatories undergo regular removal and re-coating of the aluminum? Why?

Performance of astronomical mirrors that are exposed to the environment for long periods of time can experience a slow degradation of performance. They usually need to receive some kind of regular ...
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5 votes
1 answer
518 views

Was the use of silver on 'optical' telescope mirrors more common in the past? Why?

In the past, weren't many astronomical telescope mirrors periodically removed and 'resilvered', and wasn't this actually done using silver? I'm guessing that this is much less common now - new ...
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4 votes
3 answers
132 views

Why are telescope mirrors nearly flat?

My understanding of telescope mirrors is that they are (generally speaking) a slice out of an imaginary sphere. The center of this sphere is the focal point of the telescope, where the detector is ...
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4 votes
2 answers
218 views

Need advice on mirror-making for a home-made amateur reflector [closed]

For example, what would be some good references to read first? What sort of glass slab should I use? What size; diameter and thickness. Im a first-time builder trying to build one
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4 votes
2 answers
1k views

Why do telescopes use hexagonal mirror pieces instead of pie slice shaped ones?

Some new large telescopes in the near future, on Earth and in space, will use multiple mirrors. The individual mirror pieces will be hexagonal in shape. I wonder why this shape is prefered over the ...
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3 votes
1 answer
123 views

How would a flat mirror on the Moon reflect sunlight

I was solving a task that said (paraphrasing): There is a flat mirror on the Moon, whose reflection coefficient is 100%, and observers on the Earth observe it as a star whose apparent magnitude is $...
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3 votes
1 answer
700 views

How do tip tilt mirrors correct distortion in adaptive optics?

I'm currently trying to learn about how adaptive optics correct the blurriness caused by atmospherical seeing effects. This is my current understanding of how adaptive optics works (trying to offer ...
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3 votes
2 answers
110 views

Is a mirror cell only necessary for collimation?

I'm building a truss Newtonian, and I'm planning on achieving collimation using turnbuckle-style trusses, as demonstrated in this thread. If I'm collimating this way, is there any reason to support ...
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3 votes
0 answers
59 views

Is it possible to model a solar thermal concentrator using Zernike polynomials?

This question might seem a bit off-topic, but I guess there are a lot of people here that know about optics, telescopes, etc. I would like to simulate solar thermal systems that focus solar ...
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  • 131
2 votes
3 answers
297 views

Does the size of the atom limit the focal length of telescopes?

Does the size of the atom place a theoretical limit on a telescope's focal length (and thus, resolution)? It seems to me that that the allowed margin of error for parabolic mirrors drops with an ...
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  • 580
2 votes
2 answers
259 views

Source of mirror reflectivity data

I am trying to find a source of mirror reflectivity versus wavelength for the typical protected overcoat Aluminum mirrors used in astronomy. I need this to cover the whole visible range (300-1200nm) ...
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2 votes
1 answer
123 views

What are some formulas that are associated with the Schmidt corrector?

I want to fully understand how an SCT works. Thus, I figured out I can use some formulas that describe how an incident ray that is parallel with the axis would act after refracting off a Schmidt plate....
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2 votes
2 answers
1k views

What are the aberrations of an SCT? And how can they be eliminated?

The Schmidt-Cassegrain telescope is amazing! It is compact, suitable for astrophotography ,and it requires little to no collimation. However, the SCT has some inherent optical issues. What are they? ...
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2 votes
1 answer
251 views

Can this mirror be cleaned?

I dug up my old 6" Dobsonian telescope from storage and the mirror looks like the following: The picture is down the tube, so you can see the spider holding the secondary. To my eye, the spots look ...
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2 votes
1 answer
95 views

Does a continuous deformable mirror cause diffuse reflection?

We have all seen images like this of deformable mirrors: Continuous deformable mirrors are known to have a higher quality over segmented mirrors, but it seems to me that a continuous mirror (or even ...
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  • 123
1 vote
2 answers
151 views

Why are larger hex mirrors round and the smaller aren't?

Per this diagram why are the larger (30 meter and European) mirrors filled out to nearly a full circle, while the smaller mirrors composed of hexagons retain a hexagonal border limit instead of ...
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1 vote
1 answer
200 views

Why aren't corrector plates aligned with the center of curvature in an SCT?

According to wikipedia, Schmidt corrector plates must be aligned with the center of curvature to eliminate the spherical aberration. However, in compact SCT designs by Celestron and Meade, that is ...
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1 vote
0 answers
60 views

How has the price of an amateur telescope 8-inch, f/8 finished, aluminized mirror varied over the last fifty years?

During a discussion in The Observatory I was remembering that an 8-inch telescope mirror, polished and aluminized, cost something like \$100 to \$200 US in the mid 1970's. Just now I've seen an add in ...
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1 vote
1 answer
188 views

(Thought experiment) if we put a huge mirror into space, could we see back in time to the big bang? [duplicate]

This is an addition to this question which is closed: By putting a mirror in space, would we be able to see into the past? Imagine there is a supernova a hundred years ago. Lots of people see it but ...
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0 votes
1 answer
108 views

Where do I find a better mirror? [closed]

I recently bought a telescope, but it doesn't have a very clear image. Where can I buy a better mirror?
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