Links to stuff on this blog

Use the Site Index of Projects page link above for an easier way to find stuff on my blog that you might be looking for!

Sunday, May 22, 2011

First Test: Chromatic Dispersive Schlieren Light Source

From the title of this post I bet you can guess what it's going to be about. Last week I wrote about a Chromatic Dispersive Light Source that I was building for my Schlieren setup. I managed to get time to work on it this week and test it a bit. But before I get to that I'd like to say that I'm going to abbreviate the Chromatic Dispersive Schlieren Light Source from now on as CDLS. That either stands for Chromatic Dispersive Light Source or Chromatic Dispersive Light Schlieren. Why give it an acronym? Why have the S mean either Schlieren or Source? Everything sounds better and more important if it has an acronym associated with it!! Better still if it's a little ambigious and mysterious. At some point if I mess around with this more and make it better I'll have to come up with a retronym for this version. OK I'm kidding...

Enough of that, HERE is last weeks posts about what I am trying to build. As I mentioned I ground down the bullet lens end of a white LED and polished the surface flat. Then I wrapped it in aluminum foil tape, poked a pin hole in the foil and mounted it in front of a prism. You can see a picture of the assembly HERE. One thing that I did add that is not in the picture is right after the prism I mounted a plate with a 0.1" hole in it to block and light that is bouncing off the prism. I also built a small cardboard cover with the whole thing to help block any light from coming off it.
The first attempt at using this didn't work too well because the 'rainbow' coming off the beam and out the hole was very narrow and didn't illuminate the mirror very well. I tried putting a lens after the 0.1" hole and that works better but is still not perfect. Below is a picture of what I got.

Burning Candle With CDLS
See how much better that caption on the picture looks with CDLS instead of Chromatic Dispersive Light Schlieren? What can be seen in the picture is a nice rainbow of colors caused by the refracting light from the hot air rising off the candle. Before you even ask "why are you taking pictures of candles?" Click below to read more and for the answer to that question.
To answer the question about the candle, yes there is a world full of interesting things to photograph with Schlieren photography but I keep coming back to the candle when I am experimenting with the Schlieren setup itself. Candles make a lot of hot air and that makes for good refraction and clear Schlieren effects. It's easier to start with a candle when I'm experimenting with the optics because the candle will burn for a long time while I am tweaking lenses and playing with light sources. So in this post all I have to show are pretty pictures of candles. ready for another one? Here you go!
Burning Candle With Chromatic Dispersive Light Schlieren
Not much different than the first picture really but it looks neat. Interesting that there seems to be colors in the picture that are not coming out of the prism. That means that this is working. The important thing here is that I am not using a Schlieren Stop or anything else between the mirror and the camera. I'm not cutting off the light in any way and only getting the color from the prism. That is my goal because setting up a razor edge or a colored filter as a Schlieren stop has always been a pain for me to get aligned right. I always seem to spend more time setting that up than the object or experiment that I am trying to photograph. Time for another picture:

Burning Candle With Chromatic Dispersive Light Source
The last picture doesn't show the effect as much as the first two. I'm not sure what was going on in that one because these are screen shots from the video that I made while I was changing lenses and messing around with the alignment. I'll edit and post the video later once I have time.
What I have learned from this is that the CDLS approach is going to work as soon as I figure out what lens I need and mount it in front of the prism. I have a box of lenses that I have scrounged out of various things and once I find the best one I'll build a mount for it. The lens I used for the video was taped to the prism mount and was moving all over the place while I was filming. As always if you have any questions email me at or leave a comment. I'm happy to answer any questions!

1 comment:

  1. Respected sir,
    Firstly, congrats on all your projects. Your Schlieren projects are very interesting & I would very much like to make one. I am a lecturer working in the Mechanical Engg dept. of an Engineering college in South India. We have this subject Compressible fluid flow in which the theory of Shock waves is taught. For the benefit of students, we plan to set up the Schlieren apparatus along with a wind or shock tunnel for visualising shock waves & other phenomena. I tried to get some details from the plans you have put up. I think a concave mirror of 6" dia and about 10 m focal length would be required. But such a mirror is not available here easily & I got a quote from a local supplier quoting a price on the higher side. Kindly advise on how to procure items as well as the specs required.
    Sir, we shall be deeply grateful to you for this help.
    Thanking you.

    Yours sincerely,
    Shajan K. Thomas