What is Exposure? A Tutorial


I am traveling and and have limited access to internet, hence a short reply.
There is a small sensor to read the exposure (this is separate than the main picture capture sensor). There are 3 ways this sensor meters the light.
Matrix, Center Weighted and Spot.
In Matrix the entire view finder is considered to meter the light. It will read the light from the entire entire frame and average it.
In Center Weighted, only the center 20% of the frame is used to meter the light ignoring the other part of the frame.
In Spot Metering only the center 2 % of the frame or in advance camera the focusing point is considered for light reading ignoring the other part of the frame.
I guess you were in matrix mode and when your subject moved the camera saw change in lighting. It is always preferred to use Center or Spot metering when in Manual Exposure mode.


Yes Henry I was in Matrix mode. I assumed that since Aperture, Shutter speed and ISO are constant I should get a consistent shot.
I will use spot metering for such cases now on. Thanks for your time! :)


Hi [MENTION=16765]hensil[/MENTION],

I understand that camera uses metering to decide the exposure.
If I am clicking in full Manual mode, how does metering come into picture?
The reason for this question is, Last weekend I was just playing with my D3100(in Manual mode). I shot two images (inside room), one with a person and other without a person. In both the images I could see a slight difference in exposure for the wall. What am i missing?
Both the pictures were clicked in quick succession on a tripod so i dont really think frame or light changed.
Read this.