Experiment example a small light source shows as a bright spot on dvds a larger light source spread the light to cover all areas of the cds. I did not have the perfect lights to show this however by choosing an angle near to the cds with the small light you can see the spot of light reflected I then choose a larger light and held it at the same point above the cds and no longer can you see that light being reflected from one spot it is spread over a much larger area.
With this experiment it shows that the reflected image of the large light source completely fills the DVDS in other words it fills the family of angles that cause direct reflection.
When talking about the family of angles we talk about direct reflection . In diffuse reflection for example the light can come at any angle and so is not affected by this topic.
The family of angles determines where we should put our lights in photography.
In the case of direct reflection on a shiny surface as seen with the CDS the light is directly reflected so any light placed within the family of angles reflects as bright back however if placed outside the family of angles it cannot be seen.
In the next two images I have taken one with the light within the family of angles and the other outside it.
As we often want to see the reflection of a mirror or shiny subject the important thing is to have a light source that is large enough to fill the family of angles. If with a subject we do not want to see reflected light the camera and the light must be placed in such a way so as to avoid the direct reflection.
Polarized Direct Reflection
This is so similar to direct reflection that many photographers treat it the same however it can have its uses.
Like the direct reflection it can be seen at a mirror angle to your camera. Unlike direct reflection a perfectly polarised reflection is only half as bright as polarisation inevitably involves absorption. In this case a polarised object using a polarizer on a lens can reflect little or no light/glare back and the camera cannot see it.
It is the case that the subject being photographed is also polarized and therefore will absorb light .
How can we tell if it a reflection is direct or polarised. Polarised light will be dimmer but this alone cannot tell us. Also both polarised and diffused light can be reflect and diffuse reflection.
A few guidelines in telling the difference.
1. If the surface is made of a material that conduct such as metal its reflection is likely to be unpolarised.
2. If the surface looks like a mirror for example bright metal the reflection is likely to be simple direct reflection and not glare.
3. If the surface does not have a mirror like reflection for example polished wood or leather, the light is more likely to be polarised if the camera is seeing it at a 40 or 50 degree angle.The exact angle depends on the material. At other angles the light tends to be unpolarised direct reflection.
4. The conclusive test however is to put a on the camera if it eliminates the reflection then that reflection polarised.
If we want polarised reflection increased we can do this by turning the polariser by 90 degrees. note also polariser always blocks some unpolarised light by doing this it becomes a neutral density filter that affects everything except direct reflection thus when we increase the exposure to compensate for the neutral density the direct reflection increases even more. If the reflection is not glare the polariser will have no effect except to add neutral density.
Note the sky can also be a perfect polariser by putting the subject at an angle that reflects the most polarised part of the sky can make effective the lens polarising filter.
???????????? how do I know which part of the sky is the most polarised.
So I have tried to do the experiment to show polarized light using a glossy piece of black plastic a black item and a white item. I have tried with a white light in a dark room so there was no polarised sunlight. I cannot see the difference. Help if any one can. Here is what I have.
So I am still trying to understand the above and why it did not work. Here is some more information.
I was using daylight from the Sky so this could be polarised. I have tried with an white studio light. No improvements.
What about the angle so I have tried a direct opposite angle and a 90 degree angle with my camera from the light.
Finally I managed to see the difference with a polariser. Its not exactly as comprehensive a picture as in the book however. With the camera facing the light source which is a bed side lamp with a 5500 K bulb. Both the light and the camer are at a 50 degree angle approx. I added the polariser and saw no difference until I turned it 90 degrees and finally I could see the small battery loose some of the reflection. I feel in order to do this experiment more effectively I would need a larger light source however I have learned the purpose of the polariser and the direction of Direct polarised light. It took me all day but I am satisfied now on to the next experiment.
Other Interesting Books The Photographers mind
Science Experiments from Light Science and Magic.
Direct and Diffuse Light on a shiny subject
Using Diffuse Light to show shadow
Working towards assignment 4 Light