Jump to content

sgl_imaging_challenge_2021_annual.thumb.jpg.3fc34f695a81b16210333189a3162ac7.jpg

Recommended Posts

I'm experiencing an issue with my CPC800 which is I can only describe as an issue with slew, mount drift or backlash: After a sucessfull PA (ASPA or 3 Star Align) I get the scope to GOTO quite accurately. I use the Celestron CrossAim 12.5mm eyepiece (CCelestron CrossAim 12.5mm Illuminated Reticle Eyepiece) to align on each star as accurately as possible and this has helped enourmously with GOTO accuracy. If the GOTO target is to east of the meridian the GOTO and slew are bang-on - tracking starts when the target is at the centre of the FOV. However, if the target is on the west the slew continues past the target. To stop this I have to press the handset button opposite of the direction of slew and then the tracking starts. I'm afraid I can't describe this any better - I wish I could post a video.

Please, can any explain what is going on and perhaps suggest a solution?

Link to post
Share on other sites
  • 1 month later...

Have you found a solution to this problem? I seem to be having the same problem with my CPC-800 and the HD Pro Wedge.

I don't recall having the problem at all without the wedge.

I'll play tonight and see if I can isolate it to a weight/balance problem.

Link to post
Share on other sites

I found a post on another site indicating balance may be a problem as well, and did indeed notice that when mounted on the wedge my CPC800 does tend to rotate to having the motor side down (opposite side of the carrying handle). I added some weight (about 2 lbs) with a velcro strap to the handle and it did help, but not quite enough. I still get some drift after a polar alignment when pointed toward the western sky, but 2-3 minute exposures to the east seem to have no drift now.

The scope is also a bit back-heavy and top heavy - I've only got the default finder-scope and a small camera mount, and still think a bit of the drift might be associated with that imbalance as well.

Link to post
Share on other sites
  • 4 weeks later...

The prices for balancing counterweights are too steep! 

I will stick to wrist and anckle weights for now....I have the sliding rail ATM solution for the CPC800 but not a top weight.

Link to post
Share on other sites

Hi Rodrigol,

Another thing you could try is when searching/viewing objects, try staying in the same quadrant of the sky - I know that this probably isn't the best way of doing things, but I've found - even in Alt/az mode, that staying within the same area of sky keeps the accuracy better than moving through large "Portions" of sky - not sure if you was experiencing this in Alt/az mode or not - if so, then the wedge is set up ok, but if its only started since moving to the wedge, then as mentioned, probably balance.

Next clear night out with your scope, try to just pick objects out in each quadrant, (North, south, East and West) and do a few GOTO's within close proximity of each other - try these and see how accurate the mount is then.  

I know its a little time consuming, but then switch the mount off and do a 2 star align in the part of the sky you want to try next - say change from objects in the east - to objects in the West - on alignment pick 2 stars in only the West to align on, then try GOTO for the objects only in that part of the sky - this will give you better accuracy, I've done it a few times when moving to different parts of the sky (only in Alt/Az mode) and used the "Sync" function a few times to not so much re - position the scope in that area of the sky, but to try to lock on to closer objects to maybe refine the accuracy of the mount.

I know its a little time consuming, but I've found that using this method makes the mount much more accurate, just then trying really bright objects for GOTO accuracy as these are easier to see for me under light polluted skies - there's nothing worse than not knowing if the objects are invisible due to its faint nature or just out of the FOV (trust me, I think everyone has experienced this from time to time.

Paul.

  • Like 1
Link to post
Share on other sites
  • 3 weeks later...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By benzomobile
      Hi to all.
      The most popular mounts - even those that are included in  the small-medium range group, do drive the axes rotation  via worm wheel coupling . 
      This one are plagued by the drawback that I have always considered very unpleasant: the mechanical play  is not properly controlled and it can’t be always limited within acceptable tolerance limits.
      The adjustment of  Back Lash (BL) is entrusted to two screws (more often they are grains) usually positioned at 180 ° from each other. However - as we all know, even a wheel very slight eccentric creates
      an inconstancy of contact with the worm: when the play is adjusted for an initial position of the axis, it is not in other positions. 
      In other words, there are positions where the worm rotates with adequate friction, others in which the same friction can increase significantly, and still others where it is so reduced to the point 
      that it causes excessive play. 
      So, the tuning screws are  sometimes  too tight and sometimes too loose … mission impossible to find the right compromise! 
      This behavior is already annoying in manual movement because  the task of pointing at an object  in a steady way  is not feasible because it ever  'jumps'. 
      In photography it's even worse. 
      Not only does an unavoidable backlash often  appears in Dec – and it is very badly correctable also by the autoguider software, but- and it is dirty worse, the tracking in RA does not perform evenly 
      and smoothly.  The typical ‘micro’ irregularities in  star images is what we see in our shots. 
      Many high range mounts adopt different methods to contain lashes, and the best ones adopt mechanical systems with which that error is reduced to zero. 
      With this long introduction, I will tell you what very simple modification I thought of making on my HEQ5.
      Please, stay tuned 🙂
      Beppe
       
    • By SStanford
      Hi All,
      With ongoing issues related to slewing in the EQ3 pro it's quite clear that there is some significant backlash.
      I understand there is a way to repair this myself; does anyone have details of guide for the EQ3 pro to reduce the backlash?
      I also understand that the lubricant is important to reduce backlash. Can anyone make any recommendations here too?
      Thanks again!
    • By SteveBz
      Hi People,
      I have quite severe backlash, such that guiding assistant just gives up.  It seems to be about 11 secs in total, the one time GA came back with anything, but it's about 3-4 secs if I measure it by hand.  Here's some guiding.  Actually, it's worse when I'm dithering.

      So, I tried measuring the backlash with by counting and it's about 3-4 secs.  If I used PHD2 guiding assistant, mostly it fails, or it comes back with a very big number, like 11,350 msecs.
      I tried entering this:

      But then I got a see-saw mechanism, even when I dropped 8,000 to 3,000 it was the same.
      I've taken the motor off just now and looked at the grub/hex-screw mechanisms.  One hex-screw was loose, so I tightened it to hand tight and let the grub-screw off an eighth of a turn.  I'll look again this evening.
      I ran a three hour sequence of exposures on NGC6888 (with dither) and this is what I got on EVERY image.  Amazingly, they stacked nicely.

      So last night I ran without dither and it was mostly OK.  What I want is full dither, but to do that I need to deal with the backlash.
      Here's a photo of the motor and gears, most of the backlash seems to come from the top gear (ie the 12-tooth gear and its neighbour).  I guess the rest comes from the worm-gear:

      Does anyone have any suggestions? There doesn't seem to be a belt-mod for the EQ5 as far as I can see.  Maybe there are better Dec backlash compensation settings I could use.
      Thanks,
      Steve.
    • By Corpze
      Hi, I recently made a video of how to mount a Sesto Senso focus motor to a Starlight feather touch focuser.
      I have now also made a video of how to calibrate it and also how to measure the backlash of the rack and pinion gear of the focuser.
      This method is not limited to a starlight feather touch focuser but could be performed on all kinds of focuser.

      I hope this video makes it easier for anyone out there having problems with backlash.

      You can also check out my other videos of the focuser / focus motor here: https://www.youtube.com/channel/UCm50WzpT1YKCwghW13b6k-g?view_as=subscriber
       
       
    • By joecoyle
      Hi
      I've set my scope up on it's pier in my ROR observatory, done a few drift aligns and started to take some images. 
      I've noticed a 'quite' regular dip in my DEC line on several nights. 
      Would anyone be able to have a quick scan of my log and offer any insight?
      Could it be backlash? Could it be something with each rotation of the gears? Faulty tooth? 
      It is quite regular, although not always, and always in the same direction.
      It doesn't seem to be adversely affecting imaging yet, but I've not tried anything too taxing.
      Thanks
      Joe
       
      PHD2_GuideLog_2018-09-23_200940.txt
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.