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I would like to build a Schlieren photography system with a single mirror setup*. My question is - what type of mirror (parabolic/spherical) is good or at least feasible for this setup?

The theory says that spherical mirror is the right choice since a point source is needed to be focused back to a point at similar position. However, parabolic mirrors are easier to find and get and some people seem to use them. My question is - what conditions need to be met so that a parabolic mirror is sufficient? I'm loking for data - focal lengths, mirror diameters, etc. Personal experience counts.

Thanks for any answers.

*light from a point source goes through the tested area onto a mirror, is reflected, goes through the tested area again, is focused into to a single point where there is a knife edge and then ends up in camera

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A Google search turns up a lot of info. As you say, spherical mirror is preferred in single mirror setup. Parabolic not too bad for longer focal lengths (although I didn't see the math done anywhere), but that means a longer lens on the camera and a larger room.

(I found these "poor man's" methods. I want to try the second one.)

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    $\begingroup$ Seems I didn't phrase my question accurately. My main concern was about when it is sufficient to use parabolic mirror and when the difference between sphere and a parabola is big enough to cause troubles. I'll edit my question. But thanks for the links nevertheless. I got tied up in a lot of other google searches and in the end I failed in doing such a simple search. $\endgroup$
    – zegkljan
    Commented Sep 12, 2016 at 6:12
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    $\begingroup$ There are some telescope related tags at astronomy.stackexchange.com . $\endgroup$
    – Keith McClary
    Commented Sep 12, 2016 at 14:33
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    $\begingroup$ You could also try photo.stackexchange.com. BTW, spherical mirrors are easier/cheaper to manufacture than parabolic and they seem to be widely available. $\endgroup$
    – Keith McClary
    Commented Sep 13, 2016 at 13:36
  • $\begingroup$ I did try the "poor man's method", using checkerboard patterns instead of noise. Checkerboards for various resolutions are given. $\endgroup$
    – Keith McClary
    Commented Dec 26, 2020 at 5:08

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