I tried some test shots with TTL build-in flash and find the flash compensation not showing any effect on the pics.
The settings -
Subject - A chair, a table and some posters on the wall in a room.
Camera - Nikon D40
In A mode, with aperture set to F8, shutter speed is 1/4 sec under ambient light.
When the built-in flash is activated, camera set the shutter speed to 1/60 sec. This is the default setting by the camera when TTL built-in flash is used.
I took 3 pics, at 0, -1 and -3 flash compensation at 1/60 sec and F8.
The 3 pics are similar in brightness. The histograms are also not showing much difference. I expected darker pic at -1 and darkest at -3.
I tried M mode. With similiar settings, I shot another 3 pics. Same results.
The flash compensation didn't seem to show any effect whether at 0, -1 or -3 in both A and M modes.
Next, I tried manual flash instead of TTL and repeated the test.
I am at a loss. What is the problem? Is my camera flash compensation not working or I have a wrong understanding of flash compensation application?