Why do DSLRs have a non-linear response to light?
I can only say from personal experience that my two Canon DSLRs have a non-linear response but, for reasons set out below, I believe that all DSLRs will have a similar response curve.
Our eyes have an automatic iris and, when we look at a scene involving a bright sky and darker foreground, when we look at the bright sky the iris closes and we see the clouds clearly outlined against the blue sky. When we look at the darker foreground, the iris opens and we see the darker foreground clearly. A camera cannot do that.
The first picture below is an outside scene photographed with a DSLR (my Canon 1100D) and you can see the clouds in the blue sky and the details in the garden in the foreground. Below are two pictures of the same scene taken at very nearly the same time using my DFK camera, which has a linear response. On the left is a picture taken with a short exposure and the cloud and the blue sky can be seen clearly, but the foreground is so dark that detail cannot be seen. On the right is another picture taken with a longer exposure and the foreground detail is clear but the sky is completely over-exposed and the clouds, the tree, and much of the detail in the house on the left have been lost. The response curve of the DSLR means that the detail in the foreground is clear at the sacrifice of detail of the clouds in the sky.
 | |
 |
 |
What effect this has on deep-space photography, I do not know.
Home Back to the Moon