'Bob's Knobs' & a daylight Collimation

[centroid]

Bought a set of 'Bob's Knobs' for the 10" LX200GPS, last winter, but as the scope was in Collimation, and permanently installed, I didn't bother installing them.

However, in a moment of boredom this afternoon, I decided to do so.

The main reason behind this 'thread' is to reference the 'Daylight Collimation' method as described in:

http://www.mira.org/ascc/pages/lectures/collim.htm

In order to retain much of the existing collimation as possible, I set up a piece of card, with a 'pin hole' in it, on a height adjustable photo tripod, and aligned this as described in the article.

Then, replacing one adjustment screw at a time, adjusted the 'Bob's Knob', to return the secondary mirror, to its original position. The process then being repeated for the other two adjustment screws.

Using the 'Pin Hole' enabled me to retain a reasonably accurate reference point, and hopefully, the scope collimation is pretty much back where it started from, albeit a bit of 'fine tuning' on a star may be necessary.

The beauty of this method, is that if you have a scope that's way out of collimation, you can get it pretty much to where it should be, during the daytime. Then a 'fine tune' on star if necessary.

Dave

[AstroTiger]

excellent, nice find. I was wondering about that!

As with u i had a collimated SCT, thought i would leave it as it was, then as with u, moment of madness (i hate use of the word bored!) and sorted it.

Thing is now my SCT needs testing. hopefully it will get this next weekend!

cheers again, fab find

AT

[christo]

Hi Dave,

I've got to ask as I've never come across this before but what on Earth is a Bob's Knob!

Chris

[centroid]

Hi Dave,

I've got to ask as I've never come across this before but what on Earth is a Bob's Knob!

Chris

Hi Chris

I guess it does sound it bit strange if you've never heard of 'Bob's Knobs'

In common with some other SCT's, the LX200GPS has three 'Allen Key' screws, that hold the secondary mirror mount, to the Corrector Plate.

As well as securing the secondary mirror mount, these screws also serveto adjust the secondary mirror alignment, to achieve collimation.

Its a 'fiddly' process trying to do this with an 'Allen Key' in the dark, and there's always the risk of 'slipping' and scratching the Corrector Plate.

'Bob's Knobs' replace these Allen Key screws, with ones that have a knurled plastic 'thumbwheel'. This makes adjustment very much easier, and safer.

They are called 'Bob's Knobs' because they are made, and sold under that name, by a guy called 'Bob', in the US

I'm sure you are so much richer in knowledge, now that you know just what 'Bob's Knobs' are

Dave

[christo]

Ahh, I see. Thanks for the explanation Dave. It's little things like that that makes life easier. I'll sleep well tonight sound in the knowledge of who Bob is and what his knobs are for!

Chris