Jump to content


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Help with collimating a NexStar telescope

  • Please log in to reply
8 replies to this topic

#1 SilentKnights

SilentKnights

    Sputnik

  • -----
  • Posts: 37
  • Joined: 04 Oct 2012
  • Loc: Northeast

Posted 18 January 2013 - 08:26 PM

I have a NexStar 8SE what is the best collimating device to use for a guy who is pretty much a rookie to backyard astronomy ? I seen some but some look confusing and hard to use I am hoping for something that works well and is not hard to use. Any help would be appreciated thank you !!! :bow: :bow: :bow:

#2 Tel

Tel

    Cosmos

  • *****
  • Posts: 9174
  • Joined: 31 Mar 2006
  • Loc: Wallingford England

Posted 19 January 2013 - 05:13 AM

Hi Steve,

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 ! :idea:

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 ?

http://www.youtube.c...h?v=hqRVIDj4aZA

http://sweiller.free...ollimation.html

http://www.starrynig...Collimation.htm

Hoping this helps, but if you've any further queries, I'm sure we can assist further.

Best regards,
Tel
  • Gary Z likes this

#3 Midnight Dan

Midnight Dan

    Voyager 1

  • *****
  • Posts: 11759
  • Joined: 23 Jan 2008
  • Loc: Hilton, NY, Yellow Zone (Bortle 4.5)

Posted 19 January 2013 - 09:58 AM

Hi Steve:

What Tel said. :waytogo:

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.

-Dan

#4 Bob Griffiths

Bob Griffiths

    Getting Grouchy

  • *****
  • Posts: 10717
  • Joined: 10 Oct 2005
  • Loc: Frederick Maryland

Posted 19 January 2013 - 11:52 AM

I agree with Dan...a star and an eyepiece and a allen wrench or a screw driver or Bobs Knobs...

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

Bob G.

#5 Arthur Dent

Arthur Dent

    Galactic Hitch-Hiker

  • *****
  • Posts: 3708
  • Joined: 23 Oct 2008
  • Loc: South Yorkshire, UK

Posted 19 January 2013 - 05:22 PM

+1 for Bob's Knobs.

Oh, and Art's handy chart (reproduced below)

Posted Image

Art Posted Image

#6 dobsoscope

dobsoscope

    Messenger

  • *****
  • Posts: 418
  • Joined: 24 May 2006

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



#7 coutleef

coutleef

    Skylab

  • *****
  • Posts: 4180
  • Joined: 21 Feb 2008
  • Loc: Saint-Donat, Quebec, Canada

Posted 20 January 2015 - 01:45 PM

yes you center the star with your control to move the OTA

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

#8 hamdul

hamdul

    Viking 1

  • *****
  • Posts: 786
  • Joined: 23 Jun 2009
  • Loc: Litchfield NH, USA

Posted 20 January 2015 - 04:52 PM

Steve,

Before you start messing with the collimation, what makes you think that the scope NEEDS collimation? :confused:

Fred



#9 Digital Don

Digital Don

    Vanguard

  • *****
  • Posts: 2189
  • Joined: 20 Jan 2004
  • Loc: Manteno, IL

Posted 20 January 2015 - 08:08 PM

Hi Steve,

 

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!

 

Don :usa:


  • ke4kso likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.



Recent Reviews


Imaging/Sketching Contest






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics