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.


OK, Here's what I now know!

  • Please log in to reply
3 replies to this topic

#1 c8se



  • -----
  • topic starter
  • Posts: 30
  • Joined: 05 Mar 2020

Posted 11 August 2020 - 07:24 PM

After fooling around with this stupid celestron electronic focuser, getting it work then not work, not goto requested number nor goto the numbers celestron says,etc.  Here's what I found out;

No 1:   The actual numbers of the span is 2032 to 43,530+/-  NOT 0 to 60,000. (really?!!)

No 2:   Turning CW the center screw comes OUT.  This assumes the mirror is retracting to the rear of the scope. Of course the CCW is opposite. (Not so important here,just trying to establish which direction to focus for different EP focal lengths.

No 3:  By turning the focuser all the way CW  MANUALLY, (0) then all the CCW,(40000+/_) it is 45+/- .5 turns  ( Hense the 40000 vicinity.)  So, that proves that it is NOT 60000 if in fact the steps equal 1000 per revolution.  Why celestron states that 0-60000 in instructions and on the focus utility program is beyond me.  Maybe it is just me, but I tend to follow instructions and when they are incorrect, I wonder what it should be and why it was wrong after such a long period of time and why no one seems to mind.

No 4:  CW turns reduces the number 45000 down,  CCW, the opposite......


So,  Since I could never get the thing to go below 2035+/- 100,  nor go beyond 42800+/-, I'm thinking it must be binding.  NOT the case!   I remove the the focuser and I have 2 more turns +/- down and it turns easily.  Same up.  It seems to stop 2+/- turns short of the calibrated numbers.  The a total of 4

turns that is not available.  This  after shorting 16+/- turns originally.  (60,000 - 44,000)  Didn't they know their mirror travel??


How do I know this because I took the focuser off the scope and calibrated it by going down, and applying a stop at 10 and went up to 44950 and forced a stop.  Then I moved it to 22500 and reinstalled it to the scope and calibrated it and it stopped at 2032 and 42800+/- !!!!!!!    BTW I say +/- because it never stops exactly on these  numbers!  So, Why does it do that?  I have no idea!  The only thing I know is it will NOT goto a number below the 2032 nor will it goto a number greater than 43000.


Other things that baffle me is that focus utility program does not see the focuser hooked to the telescope (yes everything is hooked up correctly) BUT, with the same hook up CPWI finds it immediately and runs it???????  When I first got it I calibrated with this hook up and with the Focus Utility with no problems??  geeeeesh!

Also, now that iit is "calibrated"  it GOTO any selected number( except as listed above) but when I request a lower number it runs all the way to the highest number and the reverses and stops at the requested number?.......geeeesh


All of this is a bit of a joke and would not be a problem where it not for the problem that with a filter wheel the ASI178mc is just out of focus. if I had 2 more turns it would focus I know because if I remove the focuser then I can turn it to focus.  That is what this is all about.  If I install my 6.3 Focal Reducer then I can focus but the planets are so small on the screen.


So, what do I know.......nothing really except like most of the celestron accessories (i.e. the wifi adapter, the A/Z mt and this focuser they are works in progress that never really progress.  


It is a shame because focusing manually is a real problem due induced vibrations and the electronic focuser does eliminate that.  


SAD, and so expensive!!!   I doubt that this helps anyone any more than it helped me.  I suppose if celestron see this they will say " yea, we've known this for years, whats the problem.  HeeHee undecided.gif



#2 photoracer18



  • *****
  • Posts: 3,558
  • Joined: 02 Sep 2013
  • Loc: Martinsburg, WV

Posted 11 August 2020 - 07:46 PM

I doubt it. When using a non-DSLR you have to space the components so the distance from say the FR to the sensor is the exact distance required for the camera to focus (they give you that number) you can fill that space up the all kinds of parts including filter wheels, OAGs, etc. Also as you focus a catadioptric scope using the mirror the focal length of the scope changes up and down so you are usually never at exactly F10 but instead usually more than that (not counting the FR). So how much the focus travel it has is less important that most think.

#3 speedster


    Ranger 4

  • *****
  • Posts: 352
  • Joined: 13 Aug 2018
  • Loc: Abilene, Texas

Posted 13 August 2020 - 06:41 PM

If you are focusing near the extremes, you are Maximizing inherent aberrations of the system.  Sensor goes 5" behind the nut or 105 mm behind the FR to operate at f/10 where it is designed for best performance (for C8's).  You can note your focuser count at true f/10 spacing and then stay within  few hundred ticks of that for various set ups.  If you can't focus, change the spacing.



    Viking 1

  • *****
  • Posts: 979
  • Joined: 09 Apr 2020
  • Loc: Scottsdale, AZ

Posted 15 August 2020 - 03:43 PM

I'm not sure why you believe that your scope focus travel range should be close to the 0-60000 of the focuser. Did you ever think about the fact that the device supports many telescopes, several larger ones, which may have a longer focus travel distance?

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 Topics

Also tagged with one or more of these keywords: accessories

Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics