Hi,
the cameras.dat is not always representative of the real zoom you get. There are two values which affect this, the Aperture angle (Also known in english as angular field of view), and the zoom. But you also must take into account a third parameter that we get because we are playing on a computer screen and not looking through real binoculars: The size of the image in yoru screen. Thus it is a bit complicated and you must tweak all of them coherently if you want to have a correct result. I'm taking big care with that in my upcoming interface mod
As for your original question (Sorry for the long previous explanation), the real life values used on Uboats were these:
-Standard watch crew binoculars: 7x (Zeiss 7x50 item)
-Special Commander binoculars: 8x (Zeiss 8x60 item)
7x50 is much better for general scanning and finding objects, specially in an unstable platform like a Uboat bridge. The 8x instead is better to see details
once the object has been detected. Hence the commander, who was called to the bridge when the crew had already spotted something, came up with the 8x binoculars to be able to have a better idea of what was out there.