Is it theoretically possible to make a custom periscope with multiple bends at different angles?

For example, a periscope that went from the bedroom, down the hallway, down the stairs, around the corner, and out the front door?

I assume that if one were to get all of the mirror angles just right and the scope material was perfectly sealed it would work just like a regular periscope.

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    $\begingroup$ There is no restriction on the number of bends but the "longer" the periscope the smaller the field of view. $\endgroup$
    – Farcher
    Jan 9, 2018 at 12:11
  • $\begingroup$ Why is the field of view smaller the longer the periscope? The light rays enter the periscope parallel (if not, then you're right), so it shouldn't matter how long the periscope is. And otherwise, you can just enlarge the size of the mirrors. $\endgroup$ Jan 9, 2018 at 12:47
  • $\begingroup$ Yes, @descheleschilder but you see objects further away... so it seems smaller $\endgroup$
    – QuIcKmAtHs
    Jan 9, 2018 at 12:55
  • $\begingroup$ @descheleschilder, Submarine periscopes, which could be quite long relative to the diameter of the tube, used a sequence of lenses to provide a wide-angle field of view. The lenses formed multiple real-image planes at regular intervals down the length of the tube. Of course, the more lenses you have, the more critical it becomes to align each one just so, and the more internal reflections, etc. These days, it's easier just to put a video camera at one end, and a video display screen at the other. $\endgroup$ Jan 9, 2018 at 13:54
  • $\begingroup$ @Farcher-Of course...But doesn't the field of view stay the same, while the image is getting smaller (like a photograph that looks smaller at larger distances)? $\endgroup$ Jan 11, 2018 at 10:05

2 Answers 2


The use of Porro prisms inside binoculars can be regarded as the two backward periscopes oriented perpendicularly.

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The first prism forms a mirror image along one direction, the second one flips along another perpendicular direction. As a result, the device reverts the inverted image formed by two convex lens in the telescope. Besides reverting the orientation of image, it can shorten the length of binoculars. However, the prisms make the binoculars heavy.

enter image description here

Also, pentaprism is used to bend the way of sight in a perpendicular manner.

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I think you've already answered your own question. This is, of course, possible, but it's fairly difficult to align things precisely. You can, for example, put two normal (two-mirrored) periscopes together, so you have a four mirror periscope. If you want to look around many corners (so not only around the corner at the end of a street, but through a lot of streets throughout the city) you have to use very long pipes, connecting the periscopes at every corner. But if the mirrors are perfect I can see no reason why (in principle) this can't be done.


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