I agree with what has been said above. This is a low budget simple scope, so do not expect too much from it - Certainly a 4mm plossl is is not really suitable.
The center cap is basically there to reduce light from bright objects like viewing a full moon. Normally you should remove the entire cap for general viewing. Years ago I started with a similar scope off EBay, I recall it has very low grade plossls and they were only 3/4" diameter.
Having said that You should be able to view with a 20mm eyepiece the planets of Jupiter and Saturn albeit very small and some of the larger stars like Sirius. Vega and Arcturus.
For a similar price there are a number of 2nd hand 8" dobsonian scopes available which will give far greater viewing satisfaction.
Clear skies
Dave Perth
