<p>You may be confused about how two-way mirrors work. The reflection coefficient is the same for light coming from both directions. You would reflect away most of your starlight.</p>

CC BY-SA 4.0
2022-12-30T06:15:33.100Z
To complement that answer, I would say that technically, yes, such a telescope *could* work, but because you’d be reflecting so much light away, you’d need an enormous telescope to get the same limiting magnitude, so it would largely offset any gain from eliminating the obstruction.
Pierre Paquette
CC BY-SA 4.0
2023-09-22T22:05:50.967Z
Additionally, one could support a mirror using a transparent sheet of material rather than rods of opaque material, but the rods of opaque material have less detrimental effect on the image than any kind of transparent sheet would.
supercat
CC BY-SA 4.0
2022-12-25T07:52:59.863Z
2022-12-25T07:52:59.863Z
ProfRob
<p>The secondary mirror on a reflecting telescope obstructs some of the light coming in and the spider vanes that hold up the secondary mirror cause diffraction spikes when imaging. Some people prefer refractors because of this. Could a two-way mirror across the entire inside of the telescope prevent this or do two-way mirrors have some properties that don't make them optimal?
<a href="https://i.sstatic.net/0Cv3N.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/0Cv3N.png" alt="enter image description here" /></a></p>

<observational-astronomy><telescope><mirror>
Could two-way mirrors be used to completely eliminate obstruction for a reflector telescope?
chowder
# Could two-way mirrors be used to completely eliminate obstruction for a reflector telescope?

(Asked by: username_0 on 2022-12-25)

The secondary mirror on a reflecting telescope obstructs some of the light coming in and the spider vanes that hold up the secondary mirror cause diffraction spikes when imaging. Some people prefer refractors because of this. Could a two-way mirror across the entire inside of the telescope prevent this or do two-way mirrors have some properties that don't make them optimal?
[![enter image description here](https://i.sstatic.net/0Cv3N.png)](https://i.sstatic.net/0Cv3N.png)

**Tags:** observational-astronomy, telescope, mirror


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## 1 answers

### Answer by username_1 on 2022-12-25. Score: 8 | Accepted answer

You may be confused about how two-way mirrors work. The reflection coefficient is the same for light coming from both directions. You would reflect away most of your starlight.

> **Comments:**
> **username_2**: To complement that answer, I would say that technically, yes, such a telescope *could* work, but because you’d be reflecting so much light away, you’d need an enormous telescope to get the same limiting magnitude, so it would largely offset any gain from eliminating the obstruction.  
> **username_3**: Additionally, one could support a mirror using a transparent sheet of material rather than rods of opaque material, but the rods of opaque material have less detrimental effect on the image than any kind of transparent sheet would.  

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