I read at Ansel Adams books years ago , he was suggesting paper black frames for composition.
How many of you use this and What is the constructing technique for 35 - 70 Zoom Cameras which always 80 or more centimeters must be distance.
I'm ashamed to admit this is a piece of Ansel Adams advice I don't follow. It should help you see the scene in front of you as if it were a matted print.
To simulate a zoom, you might make the frame sized to fit at a comfortable viewing distance, for example size the frame to simulate 70 mm when held at elbow length and then figure where on your upper arm it matches 35mm.
This would make sense for LF cameras where setting up the equipment takes some time. Having said that, I presume seasoned LF photographers will "know" what their lens sees and probably won't need a frame anyway.
For 35mm and MF cameras I don't see the point. You can just raise the camera to your eye...right?
I've actually played with this some and with LF it has real benefit given the constraints of portability. It also has real benefit where two or more are discussing a setup.
With MF and 35mm it doesn't normally add much value for me.
As to the zoom question, moving the frame closer or further from your face then correlating that to focal length is th norm. I have seen strings used where the string is marked at various points.
One place where this can be particularly valuable is for a photographer who is used to one aspect ratio (e.g. 3:2 for 35mm) and wants to "train" their eye for another aspect ratio (e.g. 5:4).
It can also be useful or very wide or very long lenses. For lenses closer to 50mm (on 35mm film), not so much.