SCT Collimation

[faulksy]

hi kerry. when i fully flocked my c9.25 my colimation was obviously out but not by miles but probably similar to yours, tried loads of methods in the end i made a duncan mask which was great and got it very close indeed, i then removed the mask and carried out a star test for the final tweek its now spot on

[kerrylewis]

Faulksy

two new mysteries:

1. What's a Duncan mask?

2. Flocking? I had never heard of this until I joined this forum. I then assumed it was a Dob thing. But you did your c9.25? Does it make any difference?

Kerry

[Laurie61]

Flocking can improve contrast, I have done several scopes and can see a small difference. Shameless link to my flocking thread

http://stargazerslounge.com/topic/186255-flocking-with-a-twist/page__hl__+flocking%20+with%20+twist#entry1939513

[earth titan]

Thanks Tom. I do have a laser collimator from my reflector days and was not sure if it was any help with a SCT. However my scope is out of collimation in the first place . Is it worth getting it back roughly with the screws before replacing them?

I'd replace the Bob's knobs and get it to the same position you are now, then fine tune the collimation. Prevents it being miles out and it really is easy with Bob's knobs.

After the laser, I used a webcam with Sharpcap to do a fine adjustment. At the moment Lyra is in a nice position for the star test.

+1 for flocking. I did mine this year and I got a good increase in contrast.

[faulksy]

Faulksy

two new mysteries:

1. What's a Duncan mask?

2. Flocking? I had never heard of this until I joined this forum. I then assumed it was a Dob thing. But you did your c9.25? Does it make any difference?

Kerry

hi kerry flocking did make a difference especially on planets, contrast is a lot better very noticable. a doncan mask is a collimation mask that you fit over the front corrector plate, the duncan design has 3 windows that you look through and when viewed through the ep it is 3 lines which you adjust your screws untill the 3 lines meet very easy to make heres a link

http://www.ebay.co.uk/itm/Collimation-Mask-for-Celestron-9-25-SCT-/300951112535?pt=UK_Telescope_Eyepieces&hash=item4612158b57

[Mr Spock]

I find when I've collimated my C925 it stays put for ages

[kerrylewis]

This has been a very useful thread- thanks everyone for the links and practical advice.

I am getting these assembled:

Bob's Knobs - on the way

Laser collimator - probably needs batteries

Duncan mask - gonna get some black card today and make one.

I think I might pass on the flocking, at least for now. In any case my scope is only a few months old and I presume that the work would invalidate the guarantee.

thanks again

Kerry

[Newfie]

Great link Chris I will have to pluck up the courage and have a go at doing mine at some point.

[kerrylewis]

Ok. Bob's Knobs have arrived, I've made a Duncan mask, new batteries in the laser, clear night forecast. We are good to go

[kerrylewis]

Right - knobs are in, things roughly lined up by looking down the tube as in Bob's Knobs' instructions. Now all we need is a star!

I've also finished making the dewshield for the Telrad as found elsewhere on the is forum. For someone with 10 thumbs I'm feeling proud of myself

[kerrylewis]

Well, I managed to get reasonable collimation using the usual concentric rings method. The Bob's Knobs are great - it must be very difficult using a screwdriver.

However, I didn't have much luck with the Duncan mask - I could not see the Y shape pattern as in the instructions. I did wonder if I the star I was using (Vega) was perhaps too bright.

Has anyone any practical experience of using this method?

[kirkster501]

No need to go to those lengths.

Just take one screw out and replace it with a BK. Then the next screw.

Collimation will be a bit out, but not too much.

Collimating it between each swap is making a real meal out of it, IMHO.

Each to their own mate.  I find my method takes about 30 minues or so to install the BK's.  The first time I did it and got the scope wildly out of collimation it took me about three hours to get it back.  It was very frustrating until I learned the method.

Whatever method you choose, even if you do get the collimation miles out, you won't damage anything; it will just take you longer to get the collimation back.

[kirkster501]

Well, I managed to get reasonable collimation using the usual concentric rings method. The Bob's Knobs are great - it must be very difficult using a screwdriver.

However, I didn't have much luck with the Duncan mask - I could not see the Y shape pattern as in the instructions. I did wonder if I the star I was using (Vega) was perhaps too bright.

Has anyone any practical experience of using this method?

Well done.  Never used the DM myself.  I also found using a PC and my SPC900 when tracking the star and defocusing it and using Al's Reticule software very useful to collimate.  You can then look at the PC screen instead of through the EP on a defocused star.