GSO Dob primary adjustment screws

[programmer]

Well I've bitten the collimation bullet after owning my dob for some months. I've avoided it (mostly) because my primary didn't have a center spot/ring. I've now done that and even given the primary a wash according to 'Astronomy Hacks' (the web preview of the book; it looks good.. anyone have it?). Hopefully the ring is centred within the .25mm (!) I read somewhere is necessary for my f5 scope, but I doubt it.

Anyway, the reason of the post is about the 6 screws at the bottom of the tube, under the primary. Three have springs, and I'm assuming these are the adjustment screws. They all have a slit in the top though, as well as being knurled, so I'm guessing they all have some part to play in the primary's correct positioning.

The other part of my question is more a couple of observations.. the screwdriver slits are seemingly perfectly cut so as to not admit a screwdriver; and secondly they are bloody tight! Are they always this tight, or is it from lack of use (I don't think the scope's been collimated since new)? I'll get a set of Bob's Knobs at some stage, but for now I'll need to persevere. Any guidance much appreciated. I have read lots of web sites and threads on IIS already.

Thanks.

PS: I might yet have questions on finishing the collimation, although previous threads answer most of my questions (I have an Orion Cheshire tube).

[iceman (Mike)]

You're right - there's 3 collimation adjustment screws (the ones with springs), and 3 locking screws.
In my opinion - ignore the primary locking screws. In fact, unscrew them and take them out. It doesn't help you hold collimation and in fact can sometimes make it worse. Your mirror needs to adjust/shift as temperature changes.

The reason the collimation screws may be so tight is possibly because the locking screws are pushing too hard on the primary.

Definitely get yourself some Bob's Knobs - they make it much easier and then you won't need a screwdrive to adjust collimation.

They should get easier to move with more use.

Well done for tackling it though - it's a must-have skill for every newtonian owner.

[rmcpb (Rob)]

The three larger ones with springs are the adjusting screws and, in my case, can be moved with no need for a screwdriver.

The other ones are locking screws and I have removed mine as I found I would spend lots of time adjusting the main screws, getting it right and then putting it all out when trying to lock it in position. Instead of using these I have installed a set of Bobs Knobs heavy duty springs and simply do not need to lock the cell in position as it holds collimation very well.

Have fun

[programmer]

Thanks for your quick replies Mike and Rob. Indeed after completely loosening the locking screws I can now turn the adjustmet screws by hand. Who would've thought! Anyway back to collimating.. And bob's knobs tomorrow.

Stinker of a day here today in Melbourne. Hope you're enjoying your public holiday.

[tbentley]

Originally Posted by programmer

... according to 'Astronomy Hacks' (the web preview of the book; it looks good.. anyone have it?).

I bought the book a little over a year ago. I would say it's excellent for beginning astronomers and still has something for those a little more advanced. There's certainly more in it for dob (or at least newt) owners than anyone else but a majority of the tips are equally applicable to all 'scope operators.
Many of the pieces of advice you will find written somewhere in these forums but it's nice to have it all in one place. Also some of the tips are for questions you wouldn't even think of asking.
If I could only keep one of my astro books then this would probably be it.
Travis

[programmer]

Originally Posted by tbentley

If I could only keep one of my astro books then this would probably be it.

Sounds like a good rap. Might have to look out for it.

[Solanum]

On the subject, can anyone suggest a site (and which specific knobs) for getting Bob's Knobs suitable for a 10" GSO dob primary mirror?

Bintel lists em, but there are no details as to how many you get for the money, nor whether they are suitable for a GSO 10".

PS Look, not one knob gag!

[programmer]

Check this thread http://www.iceinspace.com.au/forum/s...ght=bobs+knobs