- #1
Hornbein
- 2,070
- 1,694
I wanted to filter out reflections from glass. So I bought a camera with a "circular polarizing filter." It filters out polarized light, adjustable for orientation. The result confuses some cameras, so it also has a second stage which induces circular polarization.
The results were disappointing. Most reflections from glass were not filtered out at all. What WAS filterable was glare or shine, as in shiny objects. The flatter and smoother the object, the better is the glare filtered out. I wanted to figure out what the difference was.
What about reflections from a mirror? That's about as flat as you can get. No filtering occurred. The result was identical no matter the orientation of the filter. It seemed to me that any image, even of the Sun, will not be filtered out. It has to be the sort of nebulous glare in which no image can be seen. I would like to understand this.
By the way, it is possible to use the filter backward. The light goes through the circular polarizer first then the linear filter second. A backward filter has no effect at all on simple glare.
Next I tried messing around with the light from a laptop. The filter is able to shut down the light completely. Then I tried the filter backward. It has no effect on the intensity of the light. Instead I got a very clear image of Haidinger's brush. It rotated as the filter rotated. As the filter rotates though the background changes from reddish to blueish. As usual the camera cannot capture and record the brush.
Next I tried reflecting the image from the laptop from a mirror. Here is a video I made of the results. Amazing, yes? The reflected image has lines of colors of the rainbow superimposed upon it, but the original does not. Note that the effect isn't a rainbow -- the colors are in a different order. As the filter rotates the colors reverse. I also tried it with the filter backward. It looked the same.
All this is far beyond my basic understanding of such things. Any help?
The results were disappointing. Most reflections from glass were not filtered out at all. What WAS filterable was glare or shine, as in shiny objects. The flatter and smoother the object, the better is the glare filtered out. I wanted to figure out what the difference was.
What about reflections from a mirror? That's about as flat as you can get. No filtering occurred. The result was identical no matter the orientation of the filter. It seemed to me that any image, even of the Sun, will not be filtered out. It has to be the sort of nebulous glare in which no image can be seen. I would like to understand this.
By the way, it is possible to use the filter backward. The light goes through the circular polarizer first then the linear filter second. A backward filter has no effect at all on simple glare.
Next I tried messing around with the light from a laptop. The filter is able to shut down the light completely. Then I tried the filter backward. It has no effect on the intensity of the light. Instead I got a very clear image of Haidinger's brush. It rotated as the filter rotated. As the filter rotates though the background changes from reddish to blueish. As usual the camera cannot capture and record the brush.
Next I tried reflecting the image from the laptop from a mirror. Here is a video I made of the results. Amazing, yes? The reflected image has lines of colors of the rainbow superimposed upon it, but the original does not. Note that the effect isn't a rainbow -- the colors are in a different order. As the filter rotates the colors reverse. I also tried it with the filter backward. It looked the same.
All this is far beyond my basic understanding of such things. Any help?