Are the Periscope on Mig-21 and mig-23 movable?

How useful is the persicope for rear views? Why western fighter weren’t install them? From a lot of sources that they are saying Mig-21 or soviet fighters have bad rear views but they are not saying much about F-4, F-5, mirage…..

How is your choice?
To have a perscope and more room for fuel at the back or bubble canopy like F-16?