Do I have focuser sag?

[Black Knight]

I've been combating non-round stars on my Quattro for some time. Today, I've been back to basics again. Collimated the focuser, collimated the secondary, and then the primary. Everythings looking fine at the moment, although I obviously won't know how things are shaping up until I manage to get out there again. Whenever that will be!

Anyway, as I was collimating the focuser, I had a Hotech Laser in the focuser switched on so I could see where it was pointing. I noticed that if I placed a small amount of pressure on the Hotech (both up and down), the laser point would move up (or down) by around 1 cm. I was hardly applying any pressure at all, just a very gently tug. I'm thinking that maybe this could be a contributing factor in my wierd shaped stars - i.e. with a camera attached, this may be enough to pull the focuser out of collimation.

So my question would be, is this focuser sag, and if it is, how do I fix it? There are a couple of grub screws around the barrel of the focuser tube, would these be the ones I would adjust? What would I look for when adjusting i.e. how do I tell when I have adjusted enough?

Here are a couple of pics of the focuser showing the grub screws (and locking screws?) I'm talking about.