SCT collimation

[beren]

Last night I installed some "Bobs knobs" on my Celestron C5 SCT, the procedure was a little scary :Chessy_Smile: but managed to do it with no hassles. If your unfamiliar with what they are they replace the stock screws that hold the secondary on SCTs or even newtonians with their secondary mirror and make the collimation procedure much easier without the use of tools. After I installed the "knobs" the collimation was way off so I used the diagram found here http://www.asterism.org/tutorials/tut14-1.htm to correct it. Ive used this info before to aid me in collimation but being in a rush I neglected to note this phrase

"The eyepiece should be oriented upward opposite to the position of screw "A" as shown by "EP" in the diagram."

Simple mistake but I wasted a bit of time until I realised why it was it working for me :duh: Once the diagonal was adjusted bingo collimation was quickly done . Anyway lesson learnt :eartoear:

[Radar]

G'day Stu,

Nice tip mate, I never knew that the diagonal had to be orientated like that, which probably explains why my SCT has always given me headaches when it comes to collimation.

I have a laser collimater for my SCT. It projects a big square with lots of little squares (like a chess board) onto a nearby wall.

I used this device to collimate my scope and adjusted the secondary until the square was centered on the wall, but to my surprise, when I attached an eyepiece and looked at a star, collimation was way way off. I don't know if this means the draw tube or something was misaligned, but something was a miss. When you guys come over sometime, I'll show ya what I mean.

I also dislike collimating my F3.3 astrograph, but that's another whole new problem which I won't go into here. :duh:

Cheers

Ray

[AstroTasmania]

Hi Beren,

Collimating SCT's to the best possible requires that it be done without the diagonal, just using a visual back straight in. Reason is that most diagonals are not perfectly aligned. When it all looks centered the next step is on a 5th mag star with good seeing to do the final tweaks, using the diffraction rings. Takes a bit of practice though.

Clear skies...

Clear skies...

[beren]

Gday Sheviil good point with the diagonal i will try that out next time, I usually collimate straight through when using the ToUcam for planetary imaging but leave in the diagonal when conducting general viewing. Must admit since getting the planetary imaging bug I have been quite obsessive with collimating because Ive seen the difference a slight correction can give :eartoear:

Gday Ray always been interested to see how a SCT laser collimator works....does your SCT have the thumbscrew upgrade, definitely recommend it

[Radar]

Hey Stu, what is the thumbscrew upgrade for? :hmm:

[beren]

Gday Ray thats what "bobs Knobs " are :thumbsupmate:

http://img.photobucket.com/albums/v149/beren/M10f10t.jpg

Great upgrade for a SCT

[Radar]

Oh right, I thought the thumbscrew upgrade was something to do with the visual back. Yeah I have got Bob's knobs on my SCT already. I can't beleive telescope manufacturers used allen keys. Obviously the people that build them don't actually use them.