Telescope mirror wall hanger for Schlieren photography

prusaprinters

<p><a href="https://en.wikipedia.org/wiki/Schlieren_photography">Schlieren photography</a> is an amazing technique that lets you view air currents. <a href="https://en.wikipedia.org/wiki/Shadowgraph">Shadowgraphy</a> is a related, less-sensitive technique, but with this telescope mirror mount, you can do both.</p><p>Shadowgraphy is easier. Here is a shadowgraph of air currents around a waving hand. This level of sensitivity cannot be achieved without a mirror to concentrate the point light source back into the camera.</p><figure class="image"><img src="https://media.prusaprinters.org/media/prints/151708/rich_content/0cec7594-e1fd-46f2-8451-f6fb16ddb2bb/shadowgraph_hand.gif#%7B%22uuid%22%3A%225681229b-d854-4e82-92f5-a63fc3ede3da%22%2C%22w%22%3A384%2C%22h%22%3A216%7D"></figure><p>Here is a Schlieren image showing air from a hair dryer blowing around a hand. This requires a razor edge to provide a partial block of the light at the point of focus, with the camera behind this point. You'll need two or three tripods: for the camera, light source, and razor edge. Schlieren imaging is far more sensitive than shadowgraphy and can work with light in the room.</p><figure class="image"><img src="https://media.prusaprinters.org/media/prints/151708/rich_content/4420808c-7b50-4374-ac8e-fcdfc59ef8f2/schlierien_hairdryer.gif#%7B%22uuid%22%3A%22d6e580cf-02c3-4e56-9c2a-7cb1a5e43dbe%22%2C%22w%22%3A384%2C%22h%22%3A216%7D"></figure><p>Unfortunately, our apartment did not have enough room to move the camera far enough away from the mirror, so we could not benefit from the full mirror diameter, but we still got some good images of cold air flowing off an ice cube, standing waves from an ultrasonic cleaner, and breath coming from a talking mouth.</p><p>With both techniques, you need a point light source, like a flashlight or phone camera light covered with aluminum foil, with a tiny pinhole to let the light through. All of this light should illuminate the camera lens (preferably telephoto), so there is plenty of light coming in.</p><p>To do all this, you need a way to mount the mirror on the wall.</p><p>This is a wall hanger for a spherical telescope mirror 160mm in diameter with a 1300mm focal length. It is the least expensive high-quality precision concave mirror I could find, and it is available on Amazon for $70: <a href="https://www.amazon.com/gp/product/B01N7A6T6Z">https://www.amazon.com/gp/product/B01N7A6T6Z</a></p><p>This is an <strong>excellent</strong> mirror, well worth the price! A tiny pinhole of light focuses back down to a tiny spot. The smaller and tighter the focus, the better for Schlieren imaging. And because it's a spherical mirror and not parabolic, it isn't sensitive to alignment, it works from any direction, making it ideal for positioning your equipment anywhere.</p><p>Even if that mirror isn't available, this mount can be adapted for any other telescope mirror; just change the dmirror and tmirror parameters.</p><p>I mounted it on a wall with two 1-5/8" sheetrock screws. Make sure there are wood studs located where the screws go in, else the mount could pull out of the wall and drop your mirror on the floor, getting it dirty and possibly breaking it.</p><p>Once on the wall, just slide the mirror into the mount from above.</p><h3>Print settings</h3><ul><li>0.30 mm layers work fine.</li><li>Be sure to use at least 3 perimeters, especially if your filament has poor self-adhesion.</li><li>20% cubic infill is sufficient.</li><li>For additional strength, use a concentric infill on the top and bottom layers.</li></ul>