Re: Sony nxcam hxr nx5u shutts off on its own

I'm not sure if I'll totally answer your questions here, but I hope it helps.

First of all the exposure - when you zoom in you loose some iris. Even in manual setting, as you zoom in the iris will close a bit (numbers go up from 1.6 to 4 as you noted). This is normal for any camera I believe. It's not a problem, so now that you know this you can plan your shots accordingly. If going to f4 makes it too dark then you'll simply have to zoom out a bit or move closer to the subject.

For the camera shutting off, memory cards would have been my first thought. What class are your cards? Even if you tried various cards, if they were all the same class (ie, speed) then the issue could persist. However, I don't believe this is likely unless the cards are a very low class number, so you may want to call Sony service.

I hope this helps.
Eric