Originally posted by david lambright
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I posted a quick response on You-Tube - here is the link to that:
Depth of Field
At one point it looked like you may have spun the device and we saw some changes, but I couldn't see the vortexes.
This is really hard to do - I did some trials with a smaller mirror I have here but it is badly distorted and useless. I did find though, that using a piece of paper as screen is very helpful in determining the exact focal points of the lens ( I used a magnifying glass) and the mirror image. One of the problems I found is that light was making it around my lens to the mirror and was interfering. So I had to make mask for it so only the light from the lens reached the mirror. I used a hole in paper to partially occlude the light and that didn't work. It needs to be the razor slit to prevent interference.
About the best thing I could get was a weblike interference pattern which you can see with your naked eye if you look at a light source through a very tiny aperture. It will look like a web across the opening. You can do this with your thumbs and forefingers to make a small hole where the four meet together and adjust it until it is almost closed up. Well, I had that pattern across the whole mirror surface and projected that onto a paper screen so I could view it from the backside.
It was a lot of fun, but I never got any schlieren shadows. I think it really takes a big mirror with a spherical grind.
Cheers,


Hang in there
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