Single-Mirror Coincident Schlieren Camera Setup (double pass)

Yes I know I seem to go on and on about Schlieren Photography on my blog... but hey it's my blog and it's about the things that I am doing! As many people know I have been messing around with Schlieren Photography for some time now and mostly it's been the camera setup itself and not the things I am photographing that I have been playing with. My latest adventure in camera setups has yielded the best results so far. If you are a avid reader of my blog you have already seen the results of this with last weeks post HERE.

  

What I have been looking for is an even illumination of the subject matter and a high degree of sensitivity. The sensitivity issue isn't something that I feel I have optimized but the setup that I have now seems to be the best so far. Up to now what I have been doing is putting the light source off to one side of the camera. The mirror then reflects the light from the light source back into the camera but because the light and the camera are side by side the light path going out to the mirror and coming back isn't 'lined up'. From what I have read this isn't the best way to do it. A better way is to have the light going out and coming back be 'lined up' in the same optical path. This is called a Coincident Double Pass setup and that is what I built. Note: I'm not an optics person so forgive my layman's explanation of all this!

Double Pass Coincident Schlieren Setup (click for bigger view)

The tricky thing about doing it this way (other than building it) is getting everything lined up just right so the light source and the camera are both coaxial and looking at the mirror. This involves getting the beam splitter, the light source, the camera and the mirror in just the right places. The mirror I am using has a focal point of 118 inches so it's really far away from the camera and beam splitter. That means that if the positioning of anything is off by even just a little bit it wont work. Usually before building something I would try a 'hack' and hold everything in place with tape and toothpicks just to see if it worked before I took the time to build a proper setup. But because of the sensitivity of the positioning I decided that I had just better build a solid and adjustable setup right from the start (and how it works!). Below is a picture of what I ended up with. If you are interested in an explanation of Schlieren photography HERE is a short Wikipedia link explaining what it is (but not how to do it).

Asymmetrical Capacitor Lifter "anti-gravity" Experiment

Asymmetrical Capacitor Lifters seem to be a popular "anti-gravity" concept and for fun I thought that I might experiment with them. An asymmetrical capacitor is a capacitor that has one electrode larger than the other one. If the insulating dielectric between the electrodes is a gas there is a small thrust that is generated in the direction from the small electrode to the larger one. This thrust is sometimes referred to as the Biefeld-Brown effect and at other times it's considered to be a mysterious anti-gravity effect. Some experiments have seen a thrust generated in a vacuum as well as an ion wind. I'm not going to comment on the presence of any anti-gravity effect other than to say I don't know what the exact definition of anti-gravity is. If a hot air balloon is floating is it defying gravity? My understanding is that there is still a gravitational attraction between the balloon and the earth it's just countered but the force of the hot air trying to get up above cooler air. Does that count as anti-gravity?

Asymmetrical Capacitor Lifter Test - it's arcing in this picture

The experiment that I decided to try was to build a small asymmetrical capacitor and photograph it in my Schlieren setup to see if I could detect any airflow. From what I have read to get some kind of force you need to have a high voltage DC potential across the electrodes. I don't have a really high voltage purely DC supply right now. The closest thing I have is a 28,000 volt DC supply that is pulsed at 15kHz. Since that is all I have, that is what I used. 

Schlieren Photography With Laser Illumination

As the title says I have decided to give lasers a try with my Schlieren Photography experiments. Mostly because lasers are neat but also because I didn't have anything else better to do this weekend! OK Kidding I thought that the monochrome light of a laser and the 'pin point' light source that they are would work good. I think that all in all it turned out pretty well.

  

I didn't have a lot of time this week to set this up properly so it was more of a hack than anything else. The laser that I am using is a red high power solid state laser and it's in place of the LED that I have been using. HERE is a post I did awhile back showing the setup with the LED and it's almost the same as what I am using now. The exception of course is that I am using a laser and some lenses and the Sony video camera so maybe it's not even close! HERE is a summary of everything that I have done in this field up to this point for anyone interested.

  

Candle photographed with laser illumination

Above is a picture of the results and below after the jump link is a video. The point of this is the laser and not the candle and my hand of course. I think that I am getting close to having a setup that I can rely on to get good images. I just need to take the 'hack' out of it and build some reliable and repeatable fixtures to hold everything. Send me an email at ottobelden@yahoo.com or leave a comment if you have any questions about all this.

Schlieren with a Sony DCR-TRV250 Camera

While moving into my new place I unearthed a video camera that I bought 10 years ago or so. It's a Sony DCR-TRV250 and after charging the battery it still works! Yeah Sony! There are two really neat things about this camera (well three actually). The first thing is it has a great 20X optical zoom and a 700X digital zoom. The second thing is it has 'Night Vision' that lets you see stuff in low light conditions. The last thing that I didn't realize was neat until today was the I.Link as Sony calls it, in reality it's a IEEE 1394 Fire Wire interface. I didn't realize how cool the fire wire thing was until I tried to get the videos I made off the camera and onto my computer. More about that later. Anyway the first thing I thought of doing once I got this thing working was to use it to make some Schlieren videos.

If you have read my other posts and seen the videos that I was making with my FujiFilm FinePix camera (a great camera by the way) I was always having trouble getting zoomed in enough on my parabolic mirror to get a good image. That problem went away with the Sony camera and it's insane zoom system.

Sony DCR-TRV250 In My Schlieren Setup

The videos that I ended up making with this camera were more just to see if I could do it and not really all that experimental. After all everyone makes a video of a candle burning using Schlieren. One thing that I did decide to try that I hadn't done before was instead of using a razor edge or 'Schlieren Stop' was to try a Circular Polarizer instead. Above is a picture of what I ended up doing and below is a more detailed explanation.