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An angle of view in an agular extent of a given scene as imaged by a camera.
Look up the Konica Wai-Wai (17mm angle). Hard to get yes, but not "impossible".
There are many ways to measure a contact angle, but the simplest way is to use a goniometer. The image of the droplet is taken with a high resolution camera; the angle can then be measured using a protractor.
It is not a proportion. There needs to be aroubd a 75 degree angle from the ground to the base. If it is too flat the ladder can slip out from underneath you. If it is too steep you can tip back. There is usually an angle at the bottom of the ladder if that is flat on the ground then that should be the safest angle (75 degrees)
One example would be a twin lens reflex, such as the Mamiya C220. You hold the camera at a level where you can look straight down into the viewfinder, which is on top. I believe that's what you are referring to. They do, or did, make an optional prism attachment so that viewing is more like an SLR. But without that you must look down.