There have been a LOT of different models of the RPG, made by different folks. One of our members around here has a background in the Soviet military, am sure he may have better info than I do.
The RPG 7 had a fairly complicated optical sight. IIRC, it was self illuminating. There were also night vision devices that could be used. One of the reasons for complexity is flight characteristics of the RPG (it turns INTO the wind) and the max range (about 900 meters) and need to lead a moving target.
Some unclassified info on the basic vanilla RPG 7-