PHD2 not working via EQMOD

[smr]

Hi,

Last night I tried to use PHD2 with EQMOD/ASCOM and Pulse Guiding for the first time. 

The night before that, and all of the nights before that I've never had a problem with PHD2, so it's definitely something to do with choosing 'EQMOD, ASCOM HEQ5' as the Mount instead of choosing 'On Camera' as the mount. 

And to verify this, and after running out of ideas as to how to fix it I just plugged the ST4 cable in, chose 'On Camera' as the Mount and sure enough guiding was fine and working straight away.

When I tried to use ASCOM for the first time I didn't change anything in PHD2 at all, other than when clicking on the 'Connect to Equipment' button I selected ASCOM EQMOD HEQ5 as the Mount, and then went about the normal routine of letting PHD2 select a star and clicking 'Guide'.

But as soon as I clicked Guide it came up with this message which I haven't seen before...

 

 

I clicked OK anyway, and then the star just began west stepping and nothing else, then eventually saying Couldn't calibrate as the star didn't move enough.

 

Any ideas please?!

[symmetal]

From the error message I assume you were pointing to a target with a high declination. The higher the declination the less the scope has to move for a given distance in RA. So when the calibration routine did its step movements in RA, the distance the star actually moved was insufficient to get an accurate calibration reading. Hence the message that the star didn't move enough and it aborted calibration. At DEC 0 the RA moves the greatest distance for a given calibration step so is easier to accurately measure it. Hence the message to calibrate at less than DEC 20 degrees for best results.

Alan

[smr]

2 minutes ago, symmetal said:

From the error message I assume you were pointing to a target with a high declination. The higher the declination the less the scope has to move for a given distance in RA. So when the calibration routine did its step movements in RA, the distance the star actually moved was insufficient to get an accurate calibration reading. Hence the message that the star didn't move enough and it aborted calibration. At DEC 0 the RA moves the greatest distance for a given calibration step so is easier to accurately measure it. Hence the message to calibrate at less than DEC 20 degrees for best results.

Alan

I was pointing towards the Iris Nebula at 35 degrees alt. 

[smr]

So should I calibrate on a star which is a lot lower in the sky ?

[symmetal]

2 minutes ago, smr said:

I was pointing towards the Iris Nebula at 35 degrees alt. 

It's the Declination of the target that matters rather than the altitude. The Iris Nebula is at Declination 68 degrees which is too high to calibrate on with any accuracy.

Alan 

[smr]

Right so am I ok to do a calibration with the scope parked? Pointing at Polaris ?

[symmetal]

1 minute ago, smr said:

So should I calibrate on a star which is a lot lower in the sky ?

Aim towards the South where Declination 0 is higher in the sky and so is easier to track for calibration as there is less atmospheric turbulance.

Alan

[symmetal]

3 minutes ago, smr said:

Right so am I ok to do a calibration with the scope parked? Pointing at Polaris ?

No, that is the worst place to attempt to calibrate PHD as the RA movement is miniscule, and at the celestial pole the RA movement is zero.

Also never 'sync' the scope looking at or near polaris for the same reason.

Alan

Edited April 25, 2020 by symmetal

[smr]

Ok I'm not following at all. Which part of the sky in the south should I point towards, near the horizon or high up in the sky?

[symmetal]

5 minutes ago, smr said:

Ok I'm not following at all. Which part of the sky in the south should I point towards, near the horizon or high up in the sky?

Ideally you should point to a star on the Celestial Equator to calibrate. Look at Stellarium and display the celestial equator. Due to the Earth's tilt the Celestial Equator is at its highest when pointing South (from the Northern Hemisphere.) Currently the Celestial Equator is at altitude 38 degrees when pointing South.

I think you're confusing RA/DEC and Alt/Az coordinates. RA/DEC are what is important to PHD2 calibration.

Alan

Edited April 25, 2020 by symmetal

[symmetal]

In the screenshot, looking South the Celestial Equator, 0 Dec, is the ligher blue horizontal line running through the word Sextans. Any star between DEC 0 and say DEC 20 degrees is fine for calibration but the closer to DEC 0 the more accurate it is.

Ensure Stellarium is displaying EQ coordinates and not Alt/Az.

Alan

[smr]

ok thanks, I just pointed the scope south and did a test calibration. It worked and is guiding without any errors, though the star SNR wasn't a very high number, should I wait until astro dark to do a proper calibration... and also when it started guiding it asks if I want to automatically restore this calibration when this profile is used. Presumably I should say yes to that? 

[smr]

would regulus be a good star to calibrate on ?

[symmetal]

12 minutes ago, smr said:

ok thanks, I just pointed the scope south and did a test calibration. It worked and is guiding without any errors, though the star SNR wasn't a very high number, should I wait until astro dark to do a proper calibration... and also when it started guiding it asks if I want to automatically restore this calibration when this profile is used. Presumably I should say yes to that? 

Glad you got it working. . If your guide scope system isn't disturbed between sessions then yes, you can restore the calibration OK. If the guide scope ends up getting rotated a little when setting up your gear, then you need to do a calibration at the start of each session. Changing targets during a session is fine and no recalibration is needed as PHD2 is aware of the declination of the scope and can scale the RA guiding movements accordingly.

ALan

Edit. Yes, it's best to wait until it's darker and you get a good star SNR for calibration though it doesn't need to be full astro dark.

Edited April 25, 2020 by symmetal

[symmetal]

2 minutes ago, smr said:

would regulus be a good star to calibrate on ?

It's in the right position but is too bright and will saturate the guide camera. You want a fainter star that has a nice peak in its profile and not a flat top like Regulus would have. You want to keep the guide exposures around 2 seconds when calibrating to average out the seeing distortions. A star SNR around 100 or so is fine.

Alan

[smr]

I can't find any stars with 100 SNR and 2 second exposures... 4 second exposures are showing an average snr of 35

[symmetal]

7 minutes ago, smr said:

I can't find any stars with 100 SNR and 2 second exposures... 4 second exposures are showing an average snr of 35

It depends on your guide camera/scope combination. I think PHD2 says a SNR over 10 or so is Ok but I never find stars with a SNR that low. Even very faint stars which are not good to guide on give me an SNR of around 50. If the star profile is stable and doesn't jump around too much from one exposure to the next then whatever SNR figure you get with an exposure around 2 secs should be fine.

If you have your guide scope gain up very high in order to see the stars the SNR figures will be lower. Try reducing your guide scope gain if possible until at least one star in your FOV has a good profile and higher SNR.

Alan

Edited April 25, 2020 by symmetal

[kryptonite]

There's a couple of really good PHD2 videos on Youtube that are well worth a watch. Found them very helping in setting up my guiding. This is part 1 - he also has a part 2. Takes you through the important settings for good guiding.

 

 

[smr]

Ok so I did the calibration earlier as you said, and it was guiding. I've just polar aligned etc. and slewed over to the target I'm imaging in the North and I opened PHD2, chose a star and clicked Guide and it just started guiding without doing any of the west step clear backlash stuff etc. that it used to do when I used an ST4 cable. Is that normal ?

[symmetal]

1 hour ago, smr said:

Ok so I did the calibration earlier as you said, and it was guiding. I've just polar aligned etc. and slewed over to the target I'm imaging in the North and I opened PHD2, chose a star and clicked Guide and it just started guiding without doing any of the west step clear backlash stuff etc. that it used to do when I used an ST4 cable. Is that normal ?

Yes that's normal if it's set to automatically restore calibration as you mentioned earlier. PHD2 pulse guiding knows the Declination you're guiding at so automatically scales the RA movements according to the declination you were at when you calibrated. It also knows when to reverse guiding directions after a meridian flip. Using the ST4 cable, it's more basic and doesn't do this so you have to calibrate every time you change to a target at a different declination or the other side of the meridian.

Alan

 

Edited April 25, 2020 by symmetal

[smr]

28 minutes ago, symmetal said:

Yes that's normal if it's set to automatically restore calibration as you mentioned earlier. PHD2 pulse guiding knows the Declination you're guiding at so automatically scales the RA movements according to the declination you were at when you calibrated. It also knows when to reverse guiding directions after a meridian flip. Using the ST4 cable, it's more basic and doesn't do this so you have to calibrate every time you change to a target at a different declination or the other side of the meridian.

Alan

 

Thanks very much for your help, it makes sense now.