Metering P vs. M???

[Merlin_AZ]

I have a new SL1 with kit lens.

I was on a recent trip where most of my shots were indoors with poor lighting using popup flash. (Yea, I know, I'm not getting a speedlight any time soon.)
Focus wasn't as crisp as I would like, and many shots looked soft. I didn't realize it until I got my files home on my computer.
I disabled my AF-assist light before the trip since it's so obnoxious, but the focus lock was still very quick, so I didn't think it would make a difference, but apparently I was wrong. It's now on again.
I'm experimenting with some things to try to make my focus better.

I was sitting in my dimly lit study today, and under P-mode as a starting point, it showed 1/60, f/4, iso-400, for a correct exposure with the flash up. The shot looked OK.
I then switched to Manual, and entered the same settings. The meter shoted it to be way underexposed, using the same settings, but the shot still looked OK. I had to change the shutter speed to 1''3 to get the needle to the center of the meter, but then, of course, it was overexposed.
Can someone explain to my why the same settings in Manual moved the needle to underexposed when it looked fine in P-mode?

I hope I explained myself clearly enough.
Thanks in advance.

[cicopo]

If I understand your question correctly the shot in P knew the flash would fire but the settings required in M did'n t know you were going to use the flash. That set of Tv / Av & ISO should have produced a decent image WITHOUT the flash but you'd need a tripod or something to hold the camera steady for the shot. 

[Merlin_AZ]

Thanks for the reply.

The flash was up.

One thing I still can't get my head around.
Am I to understand that the meter is useless shooting indoors with flash in Manual-mode? But it's OK under Auto/P/Av/Tv?
If I can't trust the meter in Manual, how am I supposed to get a "correct" exposure in Manual with flash up, shooting handheld?

[Skirball]

The meter will tell you where the exposure level is for the camera settings (not the flash), relative to what the camera thinks is proper exposure.  The meter is still useful in manual because it can give you an idea of where the settings are – if you’re in the ballpark.  The flash however, even if the camera is in manual mode, will be set to an automatic mode (TTL) where it will try to expose the subject to what it considers the proper exposure.  You have to control the flash power (plus or minus ‘proper exposure) through the flash exposure compensation.

So, if you’re shooting indoors, you can set your camera in manual to exposure the ambient surrounding slightly darker (say 1 – 2 stops) than ‘proper exposure’, and the flash will try to pull the subject up to proper.  It can create very nice photos, as the subject pops from the background.

[Merlin_AZ]

Thanks for the response.