Help with collimating a NexStar telescope
Posted 18 January 2013 - 08:26 PM
Posted 19 January 2013 - 05:13 AM
There's much been written on the subject of Schmidt Cassegrain telescope collimation and of tools reported to ease the process: noteably lasers. However, in my opinion, those which are perfectly suitable for Newtonian 'scope collimation are useless for this task while those claimed to be suitable for SCT collimation, are expensive and apparently still unproven, judging by a lack of any vast number of reviews that I've ever seen !
In essence therefore, all that is needed is one's viewing eye, a clear still night sky and an ambient temperature, acclimatised 'scope, (in this case your 8SE).
However, there are one or two "tools" which might be employed on an indirect basis; namely, an artificial star, a simple webcam, linked to a laptop and, to facilitate centralisation of the out of focus star image on the LT screen, an overlaying grid pattern. The replacement of the existing collimation screws by a set of "Bob's Knobs" may also be beneficial to the adjustment process.
Perhaps these links may be of interest to you ?
Hoping this helps, but if you've any further queries, I'm sure we can assist further.
- Gary Z likes this
Posted 19 January 2013 - 09:58 AM
What Tel said.
Save your money. The vast majority of collimation devices are not helpful on an SCT. Hotech makes one specifically designed for SCTs, but it is $$$ ! The best SCT collimation device is a high powered eyepiece and a star.
Posted 19 January 2013 - 11:52 AM
I do own an artificial star and I think I replied to a recent thread about them...What is said is althouht I do use the AS to collimate my scopes I do NOT use it on my Scts...
Hoteck makes a $500 laser system for scts that reportedly works well once you set everything up correctly but for $500 bucks it is way too much money
Posted 19 January 2013 - 05:22 PM
Oh, and Art's handy chart (reproduced below)
Posted 19 January 2015 - 10:25 AM
Star must always be centred :: with the mount controls to the centre of the field of view I am assuming? ie. not by means of the screw adjustments
Posted 20 January 2015 - 01:45 PM
the key is to do this a nigth of st least good seeing. in less than average seeing you may mess up a good collimation. i found you need some experience to collimate a SCT ehen the seeing is below average (at least i do)
- dobsoscope likes this
Posted 20 January 2015 - 04:52 PM
Before you start messing with the collimation, what makes you think that the scope NEEDS collimation?
Posted 20 January 2015 - 08:08 PM
Schmidt-Cassegrains are probably the easiest scopes to collimate since (normally) there is only one optical element - the secondary mirror - to adjust, and only one adjustment to make - tilt.
Here are a few 'tricks' I use for collimation.
1) Wait for a night with 'decent' seeing.
2) Collimate using the highest power eyepiece you normally observe with.
3) If you observe with a diagonal, use it during collimation.
4) Use Polaris as your collimation target - it 'doesn't move' so keeping it centered is easy even without a drive.
5) It is imperative that you re-center the star after each adjustment you make. Use your slow motion controls to center the star each time you turn a collimation screw.
6) You may have to loosen one screw to tighten another. However, be sure to keep at least one screw in tension at all times to prevent the secondary mirror from rotating.
7) Once you begin collimating, do not refocus, rotate the diagonal, or change eyepieces until you finish. Doing any of those things changes the 'center' of the field
It's not difficult at all, but you have to be patient and precise.
Hope that helps!
- ke4kso likes this