A slightly different approach to achieve a similar result … re-introduce the "trombone" zoom!
Push (the subject away) to make it smaller in the viewfinder and include the surrounding area … pull (the subject towards you) for final framing and focussing.
The "one-touch" manual focus zoom was very popular in the '80's and, for me, the concept soon became second nature.
Although not specifically designed for it, my Sigma 150-500mm will give me this functionality, by ignoring the zoom control and gripping the lens towards the front, I can zoom out to find and centre my often fast-moving subjects, then zoom right in close whilst panning with my eye to the viewfinder.
Even more useful now, with the improved tracking in the K-3iii
Originally posted by richard0170
If you have ever used a sportsfinder on an old fixed lens film camera you would have a much different opinion. Being able to see what is not in the frame is a great benefit. Being able to see what is approaching the frame is one too.
I've been known to use one clipped into the hot-shoe for chasing bats at night, also for when I'm using an 87 (visually opaque) infra-red filter on my CCD *istDL2 DSLR that doesn't have LiveView
As for cropping … the ultimate format has got to be square, then you can crop every which way to suit the job in hand.
No more need for battery grips and duplicate controls, just shoot everything "normally" then adjust to suit later!
A couple of etched guide-lines in the viewfinder could cover most eventualities if they were felt to be necessary.