Found this while looking for periscope FOV taken from this webpage.It says that vibration of the scopes was not that bad even at 7kts but one Commanding Officer said he did experience some but at 7kts.I will turn off this in the options for my personal game.Just posting this in case some are interested.
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Only the attack periscope can be used at Schnorkel depth in Type VII C boats as the forward air observation periscope is too short (12.2 m. = 40 ft.). The Commanding Officer of U 971 had no difficulty with periscope vibration at any speed or in any condition of sea, but there was an occasional slight shuddering with the movement of waves.
The Commanding Officer of U 672 had experienced periscope vibration sufficient to cause some blurring when at 7 knotson motors. The attack periscope has two powers - 1.5 and 6 - giving a field of view from +30° to -10°. The line of sight cannot be elevated. Standard practice was to sweep once on magnification 1.5, and then twice on magnification 6. The Schnorkel exhaust only produces a very small blind spot and sometimes none at all. The attack periscope can be raised 20 cm. higher than the top of the Schnorkel.