Today an update was posted for Canon and Nikon ViewFinder app. The main new feature is an auto focus switcher. It is placed in the right bottom corner of the main window and is used to turn on / off the auto focus of the viewfinder.
In general, Magic ViewFinder uses the central area to focus constantly with a moderate speed (non-aggressive AF, as Google describes it). So if you need to shift the focus from the central part of the frame, use AF switch.
NOTE: AF switch may behave in different ways on some Android devices. If you think you see such behavior, please report to me.
This new feature will spill over to other versions, including Universal, very soon.
Also the update 1.8.3 has improved display of non-(16:9) frames, especially in situations where the the lens view is wider than the view of the Android-device camera. Those using the anamorphic setups will appreciate the improvements.