I have like 60GB free space left on my phone and I set up mirrors so that I can see the screen still. I have ran into focus problems before but not since I upgraded to the 6S but thank you for your feedback it's much appreciated and I've never thought about the view finder thing that's an awesome idea.I used to use my phone, which had great quality video, but the problem I ran into was running out of space which really limited how long I could film for, so I felt rushed while filming. I also found it difficult to know when a video was focused, because I wasn't able to see the screen. (I used the back camera because it gets WAY better quality than the front camera.) I know there is a way to give your phone a viewfinder (you can like connect to another device with Bluetooth or something) but I've found it a lot simpler to just use a normal camera. Another thing I prefer about having a camera is having a SD card that I can just put into my computer, instead of connecting my phone with a USB cord.