Tektronix 5513 slightly out of Focus on both channels

[andypandyplod]

I have a Tektronix 5513 dual beam scope,which has a small problem where both channels cannot be completely focused with or without being connected to a signal.This has not just happened,it has been like it on getting the scope. In comparison I have an older Tektronix 543 scope which has a brighter better focused beam.
Any ideas please?

[David Hess]

I assume you mean 5112 dual beam or 5113 dual beam bistable.  Start by checking the astigmatism as described in the manual; make sure the beam spots focus in both the horizontal and vertical directions at the same point where the focus is best.