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Sunday, July 25, 2010

Homemade Schlieren Photography Setup with DIY Optics

I'm not an optics or photography expert but I thought it would be fun to try and make a Schlieren Optical setup with my son. The main reason I tried to do this is the pictures look really really neat like the below picture we took of a candle. I also thought it would be a good summer science project for Otto Jr. We had to do candle pics because that seems to be the quintessential picture that everyone takes!!
Our first Schlieren Photo of a Candle Burning
From what I know Schlieren optical systems let you see and photograph differences in fluid densities by using refraction of light. Refraction happens when the light passes from one medium (like air) of a given density into another medium (like water) of a different density. The most obvious example is looking at something that is partially in water and partially in air because air and water have very different densities. The amount of refraction or 'bending' caused by the 2 different densities is the refractive index. If you look at a straight stick partially submerged in a swimming pool or a straw in a glass of water they look bent because of refraction. In my setup it's different densities of air that are causing the refraction but it's the same principle.
Click below to read more about our first Schlieren setup!
Our second Schlieren Photo of a Candle Burning
The setup that Otto Jr. and I made to take these pictures is looking at the different densities of hot and cold air. Hot air is less dense and cold air is denser than the hot air. If you look at the pictures you can see the flame of the candle and around / above it the hot air rising and flowing away as lighter and darker regions in the picture.

Here is how (I think more or less) Schlieren Optics work: As I mentioned I'm not an optics or photography expert so this explanation is just my interpretation of what is happening. To figure out how this kind of stuff works I like to think of it kind of backwards. Imagine that you have a set up and ready to go optical arrangement with no object in the viewing area. Everything is focused, there is a consistent temperature density of air, and all you see is a blank evenly lit screen. All of the light from your light source is passing through the optics and to your camera. Now you place something hot in the optical path or disturb the airflow in some way. The light that is not passing through the 'disturbed air' makes it through OK but the light in the disturbed (different density areas) is refracted away and never reaches your camera. The areas of refracted light that never reach your camera look darker than the other areas that are passing through OK. In practice the light doesn't get refracted completely away and the incidence of refraction will vary by very small amounts so what you see is varying lighter and darker regions that correspond to the density variations.
Schlieren Candle Video with Homemade Optical Setup
In the video above you can see Otto Jr. bring a lighter into the viewing area and press down on the button releasing some of the gas which you can see flow out of the lighter. Then he ignites the lighter and lights the candle. He then plays around with it a bit and gives the "thumbs up!" There are a bunch more videos that we made on My YouTube channel. A really neat video we made is HERE that shows the heat from the candle wax rising up after we blew out the candle. Another cool video we did HERE of the candle and us messing around with the lighters.
Here is the setup we made to take these pictures and videos:

1) Camera - Fujifilm Finepix J38
2) Knife Edge - razor blade on adjustable stand
3) Lens - 5 inch 3-dioptre Florescent Workbench Light Lens
4) LED Light Source - Modified Radio Shack 276-0005
Most of the DIY Schlieren setups that I found on the internet required a parabolic mirror and I don't have one so I used a lens instead. I think the disadvantage of a lens over a mirror is the light passes by the viewing object once with a lens and twice with a mirror but the lens seems to work OK for us. Below is a hand sketch of the setup we used.
Homemade Schlieren Setup (Click on Image for a better view)
The first thing I did was take the 5" lens out of my workbench magnifier light and mount it to a pine board with a 4-7/8" hole in it. HERE are a bunch of pictures of similar magnifier lights in case you are not familiar with what I am talking about. The lens has a 3-dioptre focal length which means that the focal point is 1/3 meter away from the lens or about 13 inches. The longer the focal length the better to give the refracted light time to spread out a bit. I built a small A-Frame base for the pine board holding the lens and put in 3 wood screws for a adjustable 3 point mount. I painted the board black because I thought that might work better and not be shiny and chamfered the hole on the back side from the lens so the wood slopes away from the lens.
In the above picture you can see the board with the lens, the candle we used and in the upper right corner a dial indicator clamp that is holding the modified LED light source.
For this to work correctly we needed a 'single point of light' or a collimated light source. From THIS page I found  a description of how to modify an LED for this kind of Schlieren setup. I had a high intensity Radio Shack Jumbo White LED that has a 28500mcd brightness and I wasn't using it so we started with that.
LED's like this one are usually bullet shaped with a rounded head that acts like a lens and spreads out the light. That is not what we want so I cut the rounded lens end off just above the part of the LED that makes light (the die). After cutting it we sanded and polished the surface flat with 1500 grit sandpaper and water until it was as shiny and smooth as I could make it.  Check out the link above to see what I mean. We covered the LED's leads with heat shrink tubing and put two 39 ohm resistors in series so it would run on my homemade 5 volt power supply. The last step was to cover the LED in aluminum tape and poke a small hole with a 0.02 dia wire right over the light emitting part. The aluminum tape covers the LED so the only light coming out of it is from the small hole I poked in it. I put the LED on the end of the dial indicator stand because that allows for fine positioning the LED while focusing. it in the lens. Check out the above link for more details of the LED modification, I did exactly what he did.
The next thing we made for this was the adjustable knife edge. For this we used a razor blade (that's what everyone else uses!) and mounted it to a X-Y adjustable stand that I have. As it turns out the positioning of the knife edge wasn't that hard so I think the fine positioning of the stand is overkill. Although I don't quite understand it all (I'm not an optics or photography expert) the knife edge is used to block out the light that is refracted away from the image of the object and you need to position it so that it is partially blocking the light right at the focal point of the lens. (or mirror if that is what you have). You want a thin knife edge to get the light to refract around that edge as well. In our setup it wasn't that hard to get the edge in the right spot and it didn't actually change the image that much when I moved it.
In the above picture you can see the X-Y adjustment base sitting right in front of a camera tripod where we put the camera. In the upper left corner of the picture there is part of a small round mirror that I used to see the back side of the camera while I was adjusting the lens and the light source. This was a handy way to see what the camera was viewing while I was messing around and trying to get everything set up.

In the last picture (above) you can see the camera on the tripod focused on the lens with the knife edge and the candle. In the upper right is a heat gun that we messed around with when the candle wasn't fun anymore.
We made all the pictures at night with the windows open so it would be dark and cold in the room (cold for maximum air temp difference). To get everything set up we turned on the LED and put the lens about 26" in front of it because of the 3-dioptre focal length. We then put a piece of paper on the other side  of the lens about 26" away and moved it in and out until the light spot on the paper was as small as we could make it. That is right where we placed the edge of the razor blade and positioned it so it was just covering part of the spot.
The last step was to put the camera on a tripod right behind the razor blade and zoomed the camera as far as it would go so the magnifier lens was filling the entire shot. Once that was done I adjusted the LED around until the lens looked like a big ball of bluish light and was pretty much evenly illuminated. This all took a lot of time - and I mean a lot of time messing around to get it all in just the right spot. I have never done this before so it was all pretty much trial and error until it looked right. The camera  - lens - LED position was really sensitive but the mirror on the backside of the camera was a big help to see what I was doing.
Refer back to the hand sketch above that shows the layout if all this isn't clear. Once everything was set up we turned out the lights and lit the candle. I don't think that either my son or I had high hopes for this experiment but it turned out pretty good all things considered. I plan on refining and improving the setup and when I do I'll post more details about the experimentation and the results. Email me at if you have any suggestions for improving this or any errors in what I have described or if you just want to make your own and have questions. As I have already mentioned I'm not an optics or photography expert so I'd appreciate any help I can get!!!


  1. Thanks for such a descriptive explanation . I really appreciate you work. I am Deepak .S.Jain Research Assistant at IIT-Bombay, mumbai, India. I am working on dual wavelength schlieren. Actually I am very interested in the small setup like this which can be made even at home I would like to know more in details about this..

  2. Deepak,

    Thanks for the comment. I have a lot of information about Schlieren setups. I built a reflective Schlieren system that works much better than this refractive one I wrote about here. Check out these posts:
    If you have any questions let me know. I'm happy to help!
    - Otto Belden

  3. Sir, is that the parabolic mirror is necessary? Because I am finding it little difficult to procure it and can you suggest me some reference book which could give me some insight.Sir actually I want to use this setup to do experiments on our nozzle that we designed.

  4. The mirror is an 8 inch F7.38 parabolic mirror. A mirror is the best way to set us a Schlieren system. You can use a lens like I did in this post but there is chromatic aberration that you have to deal with.
    Check out these posts:
    There are some good quality inexpensive parabolic telescope mirrors available from China on E-bay. I recommend that you get the biggest mirror with a very long focal length that you can afford. You will get the best results that way. A cheap mirror with a short focal length will give poor results.
    Feel free to ask me any question that you may have. I'm happy to help :-)
    I hope you enjoy my blog! Otto

    1. Sir,Thanks for your reply on Schlerien.Well i have heard of another technique called as SHADOWGRAPHY can you pleas shed some light on it.

    2. Anonymous,

      I have read about it and it is similar to the technique that I am using. What would you like to know about it?

      - Otto

  5. Hi Otto

    Really nice work. I've been working on electric field imbalances as it applies to airfoils,

    Do you think the airflows around the wing/propeller could be photographed using this technique?

    Would you be interested?



    1. Nick,

      Nice video. Yes you can use Schlieren to watch the airflow. I did that on one of my posts where I made a ion lifter and photographed it using Schlieren. Check it out by clicking on the Schlieren topic at the top of the right sidebar on my blog.


  6. Hi Otto. First of all thank you very muc your blog is very helpfull.
    Can prism be used and if yes did you have suggestions like to one to look for parabolic telescopic mirrors on e-bay?

    Thank you very much.


    1. Stefano,

      Check out my other Schlieren posts, I have used a prism for this. I have some experience with parabolic mirrors on the net. Get one with a long focal length, the longer the better. remember you have to have enough room to set it up!