This app was mentioned in 1 comment, with an average of 3.00 upvotes
I don't know what kind of phone you have, but you might want to search for "director's finder app." Here's one for Android: https://play.google.com/store/apps/details?id=com.distantblue.cadrage&hl=en
And one for iPhone: https://itunes.apple.com/us/app/artemis-directors-viewfinder/id324917457?mt=8