Guiding on an EQ6R-Pro - whats your seeing like?

[NoelC]

I'm guiding my EQ6R-Pro mount at F8, which gives me a resolution on my imaging chip of about 0.6"/pixel.  I need to use this resolution (at this time of year) in order to photograph galaxies at any reasonable  scale at all.  However, this requires me to achieve good guiding (sub arcsecond) which I am nowhere near achieving.

On 22nd April (at about midnight) I got 0.8" RMS according to PHD, that included peaks of ±2".  Obviously under these conditions my subs look quite woolly.  I've considered getting the mount tuned to achieve better performance as the Periodic Error is ±10" unguided. 

(8 passes of the worm periodic error plotted in PECREP)
I'm currently using EQMOD, with ASCOM guiding, which corrects for periodic error, but it seems to make little difference to the overall guiding performance.

Is this just due to conditions (the breeze has been high here during the day, with the odd gust at night)?
What guiding figures do others get?

The target here was in LEO which was just through the zenith as guiding started (got 0.8"RMS at 22:45).
The guide cam was working at twice the scale of my imaging cam. PHD exposure was 1 second (to try to keep things centred - slowing it down to several seconds made matters far worse) with a guide star s/n of over 10. Guiding got steadily worse by 00:45 to over 1" RMS by 00:45 PHD was starting to report star lost fairly regularly.

What guiding performance (in arcseconds) are you getting?

[The Thing]

Hi Noel,

Try using the PHD2 Predictive PEC Guide Algorithm (PPEC), thats what I use. I used to record and replay PE correction in EQMOD which is good, but this works better as it corrects the PE as it is reflected in the guiding.

BTW I think your guiding figures aren't bad, it mostly depends on the seeing once you've corrected PE. Are you using an OAG? I find its better to use a finder guider as at f10 on my 8" Meade SCT using an OAG stars are ridiculously dim and fairly distorted. Its 4"/px on the 190mm fl finder with QHY5L-IIand 0.39"/px on the main ASI294 camera in my setup. I'm not too worried about blobby stars as I think the optics were ground by Mr. Blobby himself! I got around 1" RMS guiding last night (NEQ6, bearing and belts). Maybe a 400mm scope as a guide scope would work?

[ApophisAstros]

Never had such bad guiding , rebalanced the scope just now hoping it will be better tonight
This is nearly 7 hrs.

Seemed to image ok in Ha3.5nm, have posted on forum.
Roger

[NoelC]

Thanks for that Duncan; hadn't actually read the manual (have now).  will try putting PPEC on.  Am using OAG, mostly for weight and to eliminate flexure.
Roger; interesting to see you found the seeing a bit rough too.  How big are the pixels on your guide cam? Presumably you had it binned on that run?
Will post my guiding results from tonight (if this high level cloud clears off).

Noel

[ApophisAstros]

Thanks for that Duncan; hadn't actually read the manual (have now).  will try putting PPEC on.  Am using OAG, mostly for weight and to eliminate flexure.
Roger; interesting to see you found the seeing a bit rough too.  How big are the pixels on your guide cam? Presumably you had it binned on that run?
Will post my guiding results from tonight (if this high level cloud clears off).

Noel

3.75 um
No bining
Roger

[NoelC]

23rd was a write off due to cloud.  24th got 0.6"RMS at around 10:30pm, but had degraded a lot past the zenith (to around 1"RMS). Ran with PPEC on, not sure if it made a difference, but figures were slightly better.  I balanced the scope a bit more negative, which help slightly and the seeing was fairly choppy giving rise to some quite high but short lived peaks.  Last night, the 25th, (potentially the best night in ages, clear, still, not much twinkling or satellites) was a total write off due to kit failures!! 

- Must have caught the finder in getting the scope out, and couldn't get the solver to find a solution, so spent ages fiddling about getting the scope aligned. Air temperature started to drop rapidly. Got main cam down to temperature and even got autofocus to run (APT seems to take forever to cool the chip), then lost the guide cam, then lost the main cam, then had to re-cool the chip(!), but guide cam went again then no guide cam at all - give up!  I suspect it was due to temperature or humidity, but this is after replacing all the USB cables to overcome similar problems in the winter.  Have ordered a new USB hub this morning (was using a very cheap hub).

[ApophisAstros]

Why do we do it noel

[RobertM]

Sounds like a typical Noctulus Horribilis !

Sometime(s) in the future you will look back on this and think, now how did I fix that... like the rest of us 

Robert

[NoelC]

Unfortunately it happens to us all, but I've been having a lot of connection problems recently.

I managed to get out last night, which looked very still, but I think it wasn't very transparent as the sky was quite bright at the horizon.
While setting up the gear and checking connections I noticed the hot pixels on the guide cam were quite prominent, so I tried guiding on them (as they don't move - the guiding should be perfect).
With bin X2 and X3 noise reduction the hot pixels look just like stars with a slightly square profile and a signal to noise ratio of around 13.  PHD reported guiding of 0.44" RMS with peak excursions exceeding 1" in DEC.
Visually the hot pixels don't appear to move on the screen, I can only assume PHD is jittering in it's centroid calculations due to background noise in the pixels surrounding the hot one. I was using a QHY 5IIM camera.
Anyone else tried this?
Once guiding I got under 1"RMS to start with, but it degraded rapidly out of the zenith to 1.89"RMS two hours later.

[MarkS]

Hi Noel,

I use EQ6 mounts - one is belt modified and the other is not.  On a couple of nights last week I managed guiding of 0.5" RMS but figures nearer 1.0" are more typical.  It depends on the seeing and the position in the sky you are imaging.  I typically use exposures of 1-2sec for the guide camera.  I don't generally use PEC because for me the difference it makes is marginal.

Mark

[NoelC]

Thanks Mark; I have seen other's achieve 0.5" and was wondering if that was generally achievable (clearly not).

As an aside; the connection issues I was suffering with the QHY 5II camera are apparently a known problem with PHD 2.6.7:-
https://groups.google.com/forum/#!searchin/open-phd-guiding/PHD2$20with$20QHY5II%7Csort:date/open-phd-guiding/N8Vpic4ehf0/nUK6uXlFBAAJ
Doesn't explain the other connection issues, but hopefully the new hub will sort those out.  I have ordered the Startech ST4300U3C3 USB 3.0 Hub (10X the price of my existing hub!).

[ApophisAstros]

Thanks Mark; I have seen other's achieve 0.5" and was wondering if that was generally achievable (clearly not).

As an aside; the connection issues I was suffering with the QHY 5II camera are apparently a known problem with PHD 2.6.7:-
https://groups.google.com/forum/#!searchin/open-phd-guiding/PHD2$20with$20QHY5II%7Csort:date/open-phd-guiding/N8Vpic4ehf0/nUK6uXlFBAAJ
Doesn't explain the other connection issues, but hopefully the new hub will sort those out.  I have ordered the Startech ST4300U3C3 USB 3.0 Hub (10X the price of my existing hub!).

Yes Noel i have the same guide camera and when i updated PHD2 in the past it wouldn`t work as it wasnt in the list , so went back to the previous version as i backup all important past versions as sometimes its a nightmare finding older versions on the interweb..
Roger

[The Thing]

QHY5II's have always been a bit funny. I have a 5L-II colour which works well but needs a very long timeout set in the Brain (45s is what I used to use) or it disconnects all the time. Something inside is fundamentally different to the 5II and the QHY drivers are not the best. I now use a mono Altair GPCAM2 which has always worked flawlessly.