A newer version with some editing, about my attempt to tackle with guiding setup with PHD2 and a medium-heavy load. This edition is about session 4 (see below)
session one (almost out of the box)
I had the opportunity of excellent sky condition to test my NYX101 , eager to proceed with imaging. So I started upfront with a complete photo setup, as described below.
The gear under calibration was composed of :
- NYX100 together with balancing shaft and counterweight (5kg)
- RC8 tube (8kg or so)
- imaging camera + filter wheel 1kg)
- 240mm /50mm guiding scope
- PHD2 with a QHYCCD guiding camera , both of them having been running perfectly on another mount.
This first session has been a bit frustrating , since I didn't manage to achieve acceptable guiding calibration. I have got calibration reports stating orthogonality issues, and upon running the guiding , diverging DEC an RA errors.
I have implemented the settings advised by Pegasus as regards algorithms choice and parameters on RA and DEC axes.
I have checked accuracy of polar alignment which was OK.
I'm surprised because every runs of the calibration sequence have been really long (20 to 25') , and I believe this is because calibration wasn't able to converge (axis cross-influence?)
I don't know really to cope with this situation, I'll do another attempt with a lighter configuration, to make sure this is not a matter of flexure .
Polar alignment has been a breeze, but I spend part of the night to try and fail to get acceptable guiding calibration and performances.
Session two
Another night with crisp skies and acceptable outdoor temperatures , but I decided to forget about imaging to focus only on guiding feasibility.
I decided also to mitigate the influence of mount loading , simply by limiting the load to the guiding scope by itself. I left the counterweight bar in place, without additional weight.
So the total weight was limited to about 2kg.
Calibration converged at the first attempt, with RMS errors fairly below 1".
Session three...
...is still to come, because I went back home and the sky is overcast.
My objective will be to secure guiding accuracy with a small refractor (around 2-3kg), so as to be able to produce some images if the sky is willing to.
Intended steps :
- record unguided behaviour of the mount over PE period (which is said to be about 7' and assess RA and DEC "untaming" with rapid variation of error amplitude
- try to engage calibration during a calm time
- if calibration succeeds, record guided performance
- make some images !
Session four... (edited 11/04)
I was a bit eager to test again with heavier gear , since I have achieved decent guided with low load.
So I decided to skip an intermediate step an try again to guide with RC8 / 50mm guiding telescope / camera and EFW
After reviewing some forum material, I started with the hypothesis that DEC unbalance is a limiting factor. So I decided to locate experimentally the mass centre of the complete gear. To achieve that I mounted everything (RC/cam/guiding scope , the later being set to an indexed position along the optical axis, so that I can achieve the same COG position every time. Then I have located the COG by looking for the balance point of the ensemble , the lower dovetail resting on a narrow object placed across the optical axis. Then I made a mark on the dovetail. When mounting the complete gear on the mount, one has to locate the COG mark in the middle of the mount upper clamp.
(Another approach would possibly be to use a "classical " mount with brakes, and measure and mark the balance point around DEC axis.)
Well, with this setting on the NYX101, I made an accurate polar alignment, et voilà ! Guiding worked as a breeze, with much shorter calibration phases, so that I re-perform calibration for each new object.
Guiding rms is well below 1" , and I have got round shaped stars on most of my pictures.
more feedback [/u] (edited 2024/01/17)
II made various imaging sessions since the end of November, and succeeded in long lasting guided sequences , both of my RC8 and also my TSA120.
Now i use the same protocol : I have an AZ/ALT mechanical mount, and I have verified the DEC balance point for the complete instrument . From that point guiding is always acceptable, with some whimsical behaviour from time to time.
And I also use a 5kg Counterweight at the end of the extension bar. I couldn't manage so far to make a precise balancing about the RA axis (my home kitchen scale refuse to weight anything about 2,5 kg...)
I had bad times with an upgrade of PHD2 , which scrapped all my settings... I simply reverted to the settings recommended by Pegasus.
Similar problem with Pegasus FW and SW upgrades, if the mount freezes and the SW doesn't respond any longer don't forget to kill the peg.something process (Pëgasus server)
Polar alignment : I suggest to polar align the mount only after the equipment is mounted, to cope with tripod flexure under load. With polemaster, alignment is a breeze.
Anyway, I'm quite happy with the last sessions,
Clear skies!
