Flaskegaard, are you sure you really want a smaller periscope view port?
I've looked through a true periscope at the "
Submarine Force Museum" in Groton Conn. and found the eyepiece lens to be close to the eye......leaving little side view, if any. It's my opinion the lens needed to be made larger than stock, filling up more of the screen. I considered the stock view was like looking out a port hole window while standing in the center of the room. Too much viewable area around the lens. I know there are mods that made this view even more "modded" when they added back room elements to the image.....but they don't address the reality issue that you shouldn't see much of anything around the outside portion of the lens.
Besides the stock periscope peripheral view looking "cartoonish", it doesn't come close to providing the necessary scaling to give you an accurate measurement. The actual view within the stock scope is not giving you the true perspective that you would have if looking through a true periscope. In other words, the stock view is not measured to give you a true 32 degree wide view (as in real life American periscopes). Depending on your screen resolution the stock game gives you either a 36 degree view, or a 38 degree view. Either way, the game puts the objects you see within the periscope "farther away" than what they should be. In the stock game, the Telemeter Divisions (the hash marks on the lens) count to 32 from top to bottom......but they are far from being usable to measure anything if the outside view is scaled for either a 36 degree width or a 38!
The only mod to correct the stock game periscope inaccuracy is
Optical Targeting Correction. You can read more in the first thread further down the post about why OTC was made, and what it corrects.