PHD2 Calibration

[Astrokev]

Hi All

I'm trying to better understand how to improve PHD guiding, and am having a few calibration problems. Can anyone please offer some guidance?

I have an NEQ6 mount and am using an Altair 10 x 60 RACI finder with ASI 120MM mini to guide.

Following the calibration instructions in PHD I've selected a calibration star near Dec 0 and just east of the meridian, using Auto-star selection.

The Review calibration graph is attached. The West and North lines at not quite at 90° and the return East and South lines are not superimposed over the West and North lines.

My mount was polar aligned using the polar scope and I think is OK. That said, PHD guide assistant suggests my alignment may be nearly a degree off, which is huge and I'm not sure is correct.

Guiding after completion of calibration was all over the place, giving a Tot RMS error of > 3-4"

So, please can anyone suggest what may be causing the poor calibration chart? Backlash may be part of the cause - I tried to reduce this using the PHD Manual Guide buttons, but this doesn't seem to have made much difference. Any suggestions would be hugely appreciated  

 

[paul mc c]

I would suggest polar aligning using sharpcap first,the polar scope can be badly off,and then in phd use the guide assistant and let this run its course,and at the end it will give you suggested seettings for youe guiding.

[Astrokev]

1 hour ago, paul mc c said:

I would suggest polar aligning using sharpcap first,the polar scope can be badly off,and then in phd use the guide assistant and let this run its course,and at the end it will give you suggested seettings for youe guiding.

Thanks Paul. That needs SharpCap Pro I think?

To use Guide assistant, isn't this done after calibration? It's the calibration that I want to improve, and then go from there.

[paul mc c]

7 minutes ago, Astrokev said:

Thanks Paul. That needs SharpCap Pro I think?

To use Guide assistant, isn't this done after calibration? It's the calibration that I want to improve, and then go from there.

Yes thats right,i had to buy sharpcap,but a tenner well spent,yes think your right about the guide assistant.......to be honest i cant remember the routine as its been a while from i done it.

[Craney]

+1 for the SharpCap Polar Align function.        It really does save a lot of faff.

[Astrokev]

12 minutes ago, Craney said:

+1 for the SharpCap Polar Align function.        It really does save a lot of faff.

Thanks Paul and Craney. 

Good polar alignment is obviously a good thing, but could poor PA be a cause of the poor PHD calibration, or is it more likely to be caused by backlash?

If it's backlash, how can I remove this before doing the calibration? I tried using the Manual Guide buttons, but couldn't tell if the mount was moving. The image in the camera image screen is too small a scale to show any movement (although I've seen a YouTube video which clearly showed this movement - it looked like the image screen was zoomed in as the green box around the star was quite large. Anyone know how to zoom in on this image to more easily see movement using Manual Guide?)

 

[michael8554]

First of all read and apply these guidelines:

https://openphdguiding.org/phd2-best-practices/

Your RA and Dec Guiderates are 0.10x of sidereal, way too low, try 0.80x as you have Dec Backlash.

Before Calibration, Manual Guide the mount North with the step size set to 5000, otherwise you won't discern any movement.

5 hours ago, Astrokev said:

PHD guide assistant suggests my alignment may be nearly a degree off

Guide Assistant reports PA error in arcmins, and 5 arcmins would be a figure to aim for. So did it really report an error of nearly 60 arcmins?

Michael

[Astrokev]

On 16/08/2019 at 23:57, michael8554 said:

 

Guide Assistant reports PA error in arcmins, and 5 arcmins would be a figure to aim for. So did it really report an error of nearly 60 arcmins?

Michael

Thanks Michael and sorry for late reply. 

Yes it was reporting a 78 min error! No idea why it was so bad. Any ways, I’ve re done the PA using SharpCap and my guide camera and it’s now just about spot on. I’ve also increased my guiderate in EQMOD to 0.4 and my calibration is now fine. This hasn’t improved my guiding (still achieving between 1 and 1.5 arcsecs, so I need to look elsewhere. Balance is the first thing on the list. Even though I can’t get under 1 a-s, star shapes are perfectly round and not large, but sub a-s guiding may make the stars smaller.