I'm confused on how AE-lock works. I was advised and also tried this. Walk into a room point at what I want to capture, lock the exposure with AE-lock. Re-compose and take the shot. In theory the shot should have the same exposure as when I locked it. I don't see this.
For example, I went into a dark room and found some light. I metered the light and my Shutter was at 1/200. To see if it was right I metered the dark spot and it was 1/60. I AE-Locked the 1/200 from the light, locked it, re-composed and the shot came out dark. My camera focused again while I pressed the shutter all the way down and took whatever shot it wanted. I was in Av mode with a fixed ISO.
This question is more about: Why didn't AE-lock keep the exposure that I metered from and focused again before pressing the shutter all the way down?