Hey guys

I'm new to this so I may well be miles off the correct technique, but I was hoping for some advice.

I was trying to take a portrait shot last night at dusk. The sky behind the subject was incredible, and I wanted that exposed correctly. I aslo knew that I'd have to use my flash to light the subject.

I turned off the flash, pointed the the lens at the sky, depressed the shutter button half way down to take an exposure reading from the sky, then recomposed the shot on the subject, and turned the flash on. Now here's my question: since the subject is alot closer to me than the sky should I have manually focused on the subject once more? Or is there a way to keep exposure lock active while refocusing on a subject that's closer, or further away than the area/item you have obtained your exposure lock from?

Does that even make sense? Really enjoying playing with the exposure lock, makes for some really interesting shots - just not sure I fully understand what I'm doing to be honest.

I have a Canon 50D

Thanks