This post is a little different to the others in as far as I’m documenting the issues I have been having with guiding, and the steps I’ve been taking to fix and improve.
Guiding is not necessarily an essential part of astrophotography, but there are times when it is indispensable. Guiding keeps your telescope + camera locked on, with pin-point precision, to allow you to take those multi-minute exposures (subs) that make up a final stacked image. Any movement of your telescope, in any direction, can turn a tight pin-prick of light into a smudge, leading to loss of clarity in your pics. Stacking lots of images with trailing stars will not lead to a magic picture that has fixed the problems with your setup.
My problems began quite recently – within the last month – but because it has only just begun to get dark at a decent hour here in the UK, and I’ve been building up my kit and testing various purchases leading up to Winter, I hadn’t really put it all through its paces. Until recently.
Polar Aligning Problem
The first problem was polar alignment. I’d polar align at the beginning of the evening using a PoleMaster, and forget about it once aligned. I used to close the program down once done because the PC I was using (a Surface Pro) only had one USB port, and I noticed that this caused disconnects when it was overloaded. However, I recently purchased a dedicated mini PC to use with my kit. This had more USB ports available, so I kept the PoleMaster software running during the evening. When I slewed to a different part of the sky, I hadn’t noticed the polar aligning would move. This was a physical problem.
I added a pier extension to my EQ6-R Pro this year. I used to grumble a little bit when I was polar aligning as latitude adjustment was sticky. I just put it down to a feature of the pier, despite me thinking the quality didn’t seem that great. Well it turned out that I had over-tightened the bolt that attached the plate to the mount. This plate fixes to the pier extension using three bolts, and this plate fits to the EQ6-R. There was play in this, so when the weight of the scope slewed, it would be off a little bit. I don’t think it would cause too much problem – however, it was one of those things that just shouldn’t occur.
I fixed this, and PoleMaster is very happy – which makes me very happy – keeping the cross-hair firmly in place now.
Guiding Problems Continued
Putting the mount back together, I took it out for a spin – checked polar alignment would stick when slewing, I then decide to force a PHD2 calibration.
This was when I started thinking I had bigger problems.
Forcing a calibration in PHD2 (pressing shift + green target) makes PHD2 run through a series of movements so it can work out what it told the mount to do, and where it basically ended up. From the movements it does, it works out how your mount behaves so that when it sends a pulse to push it subtly in the direction needed, it actually moves in that direction.
East-West calibration was fine. Nothing too concerned. But Moving North, then South set off alarm bells. The calibration would end up with this:
The error message says “Little south movement as measured, so guiding will probably be impaired. This is usually caused by very large Dec backlash or other problems with the mount mechanics.”
OK, this seems odd. I balanced my scopes – or I thought I did – but something in the DEC axis seems off.
Guiding was erratic. I ran the Guiding Assistant to see what was up. It showed a lot of DEC backlash – again, mirrors the calibration errors.
At this point I decided to satisfy PHD2 and make South a little less stressful by moving the scope up the mount. Technically this was off-balance, but guiding seemed to be OK enough at this point. Like anything, I was up against time here and decided to do a few test 3 min subs and decided to tackle the balance problem the next day.
- the friction which tends to prevent stationary surfaces from being set in motion.
On loosening the clutches, I noticed my RA axis seemed fairly OK, but DEC was stiff. I had my TSAPO65Q on here, with camera and guidescope – total wight is only about 6.5Kg – and only across a short length, but I would have at least expected movement when tipping the scope:
Here is a very short video showing this problem. The scope is off-balance deliberately towards the objective end (not the camera end) and it still shows no movement until tipped:
The interesting thing about this revelation is that it cast doubt over my balancing. Where I thought no movement in the axis proved balanced, in this case it was an assumption. So going back to the calibration steps where North-South calibration was an issue, this could probably explain this.
After realising this, and spending a lot of time nudging the weights and scope on my mount, and obsessing a little too much over my PHD2 graphs – I’ve now ended up with pretty good guiding. This was making very small changes to RA Aggression and MinMo, and the same for DEC Aggression and MinMo until I got smaller movements.
The rule here:
- Any of those lines spending too much time under or over, rather than traversing back to central: Increase Aggression, reduce MinMo.
- Any of those lines going back and forth in large spikes: Decrease Aggression, increase MinMo.
- MAKE SMALL CHANGES!
Next Steps – Tuning
I’m not particularly happy with the stiction in my mount. It’s 6 months old, and when I originally had this, guiding wasn’t a concern – it “just worked”. So something is amiss, however – being pragmatic, it doesn’t warrant a return, only to get a scope back that may make me question things in another 6 months time. So I’ve taken a different route and decided to put go faster stripes on instead. This mount is great. It easily carries the payload of my scopes. So investing in better engineering seems a better approach. When my mount is back from Dark Frame Optics, I’ll update this post!