I'm still new into photogography. I am currently researching on flash photography when I came across one article that kinda confused me.. i know that there are a lot of experts around here so hope you could help me on this. Here is the qoute from the article:
"In Av, night and Tv (shutter speed priority) modes the camera meters for ambient (existing) light and fills in the foreground subject using the flash. It does not assume that the primary light source is the flash, and therefore the shutter speed it sets is the same as it would set if you weren’t using flash at all."
My question is, if the camera meters the ambient light separately or independently and sets the shutter speed (If using Av) as if it was not using a flash at all, then wouldnt it be overexposed if you add in the flash?
I made some tests on my camera, Im not sure if I did it correctly but here s what i did.
1. Without Flash, I set my camera to Av mode, set aperture to 1.8.
2. Point the camera to a specific spot and take note of the meter reading(speed = 1/15).
3. Press the shutter completely.
4. Using the same aperture, i flip up the flash of my camera and take another meter reading on the same spot. The shutter speed is no longer the same (speed = 1/30).
5. Press the shutter completely and the flash fires.
6. I repeated number 4 to 5 but i block the flash using my hand so that no light from flash will reach the subject.
Here's what I found out based on the output of my pics. Result of Item 3 exposure is almost the same as Item 5, but number 6 is a bit underexposed.
Now my confusion is, the article said that the camera meters in Av, T or M mode as if the flash is not the main source of light, why did my meter readings without flash and with flash different? Did i understand the article correctly?
Also can you guys enlighten me more on relation of flash to the ambient light or the relation of metering of camera(aperture and shutter settings) to the flash metering?How they work together to get correct exposure?
thanks a lot.