Installing Bob's Knob's on a C8

[mldee (Mike)]

Perhaps this should be in the beginners section, as I certainly class myself as being one, and a very elementary one at that.

Being the gadget freak that I am, I had to buy a set of B's K's for my C8. Now if only I knew what to do with them

I know where they're supposed to go, but how to put them in, and then what?

What I'm looking for is the "Combination C8 BK install instructions and C8 collimation instructions and What to beware of for Dummies" post. Is there one, and if not can someone who knows please advise?

[Bloodbean (Troy)]

Hi Mike,

I've got some Bobs knobs arriving shortly for my C8 and I've downloaded the instructions off their website here:

http://www.bobsknobs.com/pdf/Instructions_English.pdf

Hope this helps!

Troy

[sheeny (Al)]

Mike,

Read and follow the instructions Troy has posted.

One little tip if you can do it - it's not terribly important but helps with collimation later on.

When doing step 4 in the procedure, if you can have the scope pointing at something distinctive (I used the front edge of the tray on a neighbour's truck) while the OTA is pointing slightly downwards, then you can bring the secondary back to pretty close to collimated after each screw is installed.

If you can't do that, then your first collimation will probably take a bit longer, that's all.



Al.

[mldee (Mike)]

Thanks Troy, You've given me the confidence to proceed.

I must confess that I had read these instructions, but I was unsure if it was as simple as they suggest. I guess since so many have done it, it must be.

At least we can commiserate if something goes awry

Cheers.

[mldee (Mike)]

Thanks Al.

I'll see what I can find, the C8 is mounted on a pier in my RO observatory with 6' high walls, and the house wall is about 2m away from the door opening, so not much chance of finding a neighbour's truck there

I normally use a nearby treetop dead branch tip as a convenient reference when aligning things, but it obviously tends to wave a bit in the breeze, so we'll just have to see what we can find.

Again, thanks for the help. I'm sure we'll survive

[Paul Haese]

Ok here is the fool proof instructions that you need.

Lay your scope down on say something like the lounge or kitchen table with some cushions to prevent it rolling. Next remove one screw from the secondary and then install one Bob's knob. Make sure it is firm but not too tight. Finger tight is fine. If you are unsure of whether the screw is in, slightly pull the knob. If it comes free then you have not screwed it in far enough. Make sure each knob is finger tight.

Once you have the first Bob's knob in position then unscrew another screw and install the next Bob's knob. Make sure once again that the knob is firm and screwed in.

Follow this until you have all three knobs in place. One thing you must not do is undo more than one screw at a time. The screws hold the secondary assembly in place.

Now for quick collimation.

Using a piece of A4 white paper put a hole in the centre that you can peep through. The hole only needs to be about 2-3mm in diameter. Now holding the paper up in front of your face and standing back from the front of the OTA around 2-3m (you need to be far enough back to see all the reflections and you will know when you see them) line up all the reflections. All the circles have to be concentric, so you need to move the Bob's knobs until you get them all concentric. Make sure you loosen two off slightly before tightening another.

This might take a while to get everything concentric, so take your time. Once done though you will need to do a star test to get the final collimation correct. The screws must always be firm and not loose throughout the collimation process. Do not over tighten the screws either, you can damage the assembly.

And that is basically it.

[sheeny (Al)]

Originally Posted by mldee

Thanks Al.

I'll see what I can find, the C8 is mounted on a pier in my RO observatory with 6' high walls, and the house wall is about 2m away from the door opening, so not much chance of finding a neighbour's truck there

I normally use a nearby treetop dead branch tip as a convenient reference when aligning things, but it obviously tends to wave a bit in the breeze, so we'll just have to see what we can find.

Again, thanks for the help. I'm sure we'll survive

Yeah, well... its more important to have the scope pointing downwards while you replace the screws, than it is to have it aligned on anything. 2m is a bit close for focus, so don't worry about it. Its better to have a bit of collimating to do, then to have a secondary rattling around inside the scope...

Al.

[mldee (Mike)]

Thanks Paul for your advice,

I think in my circumstances I'll try it as you say, making sure the secondary stays in place. I've done my SW dob a few times, so not totally fumblefingered, I hope.

My main concern with the SCT was some unknown gotcha, but it appears pretty straight forward.

I'll pass on results when done.

Cheers

[DENMONKEY (Brett)]

Figuring on getting some of these for my c8 too.

An update when you're done would be excellent