Skyliner 250 - what does this knob do?

[Eastridge]

Sorry to be bothering folks with what seems like a really basic question but the manual does not seem to cover it & good old 'try it and see' doesn't seem to throw up a glaringly obvious answer.

On the focuser there is a screw knob between the 2 focus wheels. It is at right angles to the EP and goes into a small black plate with 4 normal screws.

What does it do??

[swamp thing]

I've not got a Skywatcher, but it sounds like you are referring to the lock screw on the focuser. This is used to lock focuser movement.

[RikM]

Yes, the silver thumbscrew underneath is a focus lock.

[Ganymede12]

DO NOT MESS WITH THAT THING! It locks the focuser for travel. I didn't know that and when I began fiddling with it the scope broke. Luckily the warranty was still good on it.

So anyway, be weary of the mysterious screw!

[Eastridge]

Thanks all . Glad I only did gentle movements to try and test out what it was.

Do you only use the lock for travel or can you lock it to keep an object you are viewing in focus, preventing accidentally moving the wheels and putting it out of focus?

[brantuk]

If you are using a large heavy eyepiece, or imaging with a camera attached to the focus tube, sometimes you can get a little movement ruining the focus. The screw can be done up to hold the focus locked in place so it doesn't slip.