Schlieren Images for the masses

[pezman]

Steve,

Nice! I think that if you move the candle a little away from the background (to get a little more shift of the background), zoom in on the area a little (to get higher resolution) and use a smaller aperture to get better depth of field, then it should work really well.

W/ the smaler aperture, you'll need plenty of light, so a strobe is probably in order.

Also, how large a region (max x and max y displacements) did you use? I'm going to guess 2 -- it might help to open that up a little -- say to 3 or 4.

As Ben pointed out, a color background could be helpful. The contrast on sandpaper might be a little low. I usually use a pattern of random dots on an LCD screen or I print out paper with random dots.

Here are two files that you can use to print backgrounds.

[Anders Troberg]

To get better contrasts on a sand paper, use the same technique as an optical mouse: shadows. Make sure the lighting comes from one side, that way each grain will make a small dark shadow.

This, by the way, is a good idea when taking photos of mountains. If taken when the sun is straight above them, they will look flat and lifeless, but if you take them in the morning or evening, the shadows will make them look three dimensional.

[pezman]

Hmm, thought I already posted this.

At any rate, here's Rossco's lump of coal. Apparently Santa made an early visit "down undah". The thing above it might be a heat plume.

[pezman]

Here's an example of a synthetic schlieren image taken using a somewhat unconventional technique. I would like to furnish details, but I can't since it is the subject of a patent application.

At any rate, this technique was pretty low-tech, so images made using a reasonably careful setup should be much better.

[larry cottrill]

This, by the way, is a good idea when taking photos of mountains. If taken when the sun is straight above them, they will look flat and lifeless, but if you take them in the morning or evening, the shadows will make them look three dimensional.

The same technique can be used to make far better than average flash pictures. Instead of using a flash unit that is tied into the camera, get one with a long flexible cable, so you can hold it out at arm's length (or some fraction thereof). No "red eyes" in people or animals, and a nicely "rounded" image instead of that cardboard cutout look. Even better is to use a flash unit powerful enough that you can bounce it off the (preferably, white) ceiling. Very broad light, rounded shadowing and natural colors.

By the way (he said, struggling valiantly to get back on topic), the Schlieren images you guys are coming up with are pretty nice, in most cases. Much better than I would have thought possible from such an "artificial" method.

L Cottrill

[steve]

here's the same candle picture with the settings tweaked.

max x and max y displacements = 3

the original was 9

[pezman]

Awesome!

Now let's see the exhaust plume from a PJ. The micro-lockwood would be nice, since it's a relatively small subject.

[steve]

I've watched Larry's Dynajet in a schlieren setup while he was trying to start it. Every time the engine would burp it looked like an explosion of bubbles coming out of the tailpipe.

The synthetic stuff is interesting, but seeing it in real time with your own eyes is incredibly amazing. Larry's mirror was sensitive enough that it was possible to see the microscopic differences in density of air just from the wind blowing.

more details please!!

anyway, here is another pic I made using a small camp stove. I would like to try a reynst next but I seem to be out of methanol.

[pezman]

The synthetic images can be done in real time too.

DigiFlow can accept movies as input, for motion studies of flows as well.

You can't beat the synthetic stuff for cost, ease of setup and scalability. For example, you can image the exhaust plume of a truck using trees or any other textured background as a mask.

This rules, seeing others use this!

[Rossco]

Hey all, Im back.

Thanks Pez, for that work on my images. Its about exactly all i could get out of it, so im not doing anything exeptionaly wrong, jsut my image isnt right.

By the way, thats not a lump of coal. I did like the note on getting it for chrismas tho!
It is a balled up bit of fine steel wool. I thought that this would be a good heat source for such shots.
The density you roll it determines the heat output, and burn time.
It can be rolled up and formed to any shape, stuck on a pin or bit of wire for an unobstructed flow, and produce heat without any flame. It does really glow very red for quite a while and let out a lot of unturbulant heat.

Steve, your getting some great shots going there! You tweeked that candle up nicely and the camp stove shots are Awsome.

RIGHT, now feed some video in there. I would say that it will take some real juice to run tho.

Pez, we wont tell anyone, hahaha, itll just be our little secret.
It does look great tho. Is that a true image, or a synthetic model? When you say that the technique is unconventional, is that the processing that you are working on or the shots? I know, i know, you cant elaborate, or youll have to kill us... all.

Rossco

[larry cottrill]

Somebody ought to build up a decent augmentor and set it up properly spaced from a pulsejet tailpipe or intake, and see what this technique shows. That should be considerably steadier than the unadorned ports, and might show some really interesting flow paths.

L Cottrill

[steve]

video would be interesting to try, though someone will need to explain how to do it.

I have noticed that the colored random dots background that pezman supplied works much better then the sandpaper, although this shouldn't be suprising. If I don't destroy my aerospike tomarrow I may try to get an immage of it running on compressed air again.