Serious Guiding Issues and desperation

[Kerry Green]

Hi!  I have had serious issues guiding for a couple months now.  I have tried to understand the logs, but I just can't.  It's been 15 years since I started astrophotography, but I had a significant break.  Now I am back at it and just can't figure out guiding anymore.  Any help would be greatly appreciated.

https://openphdguiding.org/logs/dl/PHD2_logs_o5JQ.zip

[Bruce Waddington]

Hi Kerry.   Yes, indeed, these look like serious problems.  We need to have more information though to help figure it out.  The mount is basically unguidable at this point and we need to learn why.  What kind of mount is it?  Do you know what guide speed it is using?  Where was it pointed when you tried to do the calibration?  Is there no ASCOM driver for the mount?  Can you use a different ST-4 guide cable?  Is there anything that needs to be initialized or configured in the mount that will force it to pay attention to ST-4 guide pulses and guide at a sensible rate of 0.5x to 1x sidereal?  Are you sure the focal length of your guide scope assembly is 388mm?

The basic problem here is that you couldn't get a usable calibration - the measured guide speeds are over 1x sidereal and the movements for RA and Dec are nearly parallel rather than perpendicular.  Beyond that, you've fiddled around with a bunch of PHD2 parameters that are just going to make things worse.  You should re-run the new-profile-wizard and then leave all the algorithm selections and guiding parameters alone.  All of your problems at this point are with the hardware. 

Regards,

Bruce

[Kerry Green]

Thank you for the reply.  I could not find a way to respond through the mobile web version so I had to wait util I was in front of a PC again.  

My mount is a Losmandy GM8 with a 492 digital drive system (non-gemini).  It is set to .2 for guiding as advised on the Losmandy group which states calibrate at .5, guide at .2.  Initial calibration was done per suggestions by rotating the Optical tube perpendicular to the RA and the RA parallel to the ground.  There is no ASCOM driver for this mount and I have used a different ST-4 cable.  There are selections for different rates and I did make sure it was set appropriately as far as I understand.  Yes, the focal length is 388mm.

I am new to PHD2.  The original PHD worked flawlessly, but that was years ago.  I have definitely fiddled with parameters out of frustration to get this to work.  I use a Meade LPI-G (monochrome) for the guide camera which is the same sensor as the ASI 120MM Mini.  The mount seems to behave as expected when using the star cross tool.  I did read somewhere that it may be better to calibrate close to the target.  Could trying this help at all?

Thank you again,

-Kerry

[mj.w...@gmail.com]

Hi Kerry

You have "Assume orthogonal axes = yes" selected in PHD2

Which I believe means you don't get a warning from PHD2 that Ortho in the Cal is awful.

So PHD2 reports ortho.err. = 0.0 deg when in fact it's more like 80 deg !

First google result was this, explains all the problems you are having:

https://blog.jpuschnig.com/astrophotography/using-an-mgen-v2-autoguider-on-a-losmandy-mount-with-492-digital-drive-system/

Michael

Wiltshire

[Bruce Waddington]

Hi Kerry.  We have no real experience with a mount this old so you should probably ask for help from Losmandy.  But some of the advice you’re following is completely contrary to the best practices for using PHD2.  Here are some important things that need to change:

 

1.       You can’t calibrate at one mount guide speed and then guide at a different mount speed.  That simply makes no sense.  Set the mount guide speed (in the mount) to whatever value you think works best for the mount then leave it alone.  Once it’s set, re-run the PHD2 new-profile-wizard and specify the mount guide speed you’ve decided on along with the other parameters such as focal length and camera pixel size.  Doing this will, among other things, calculate the correct step-size for calibration.

2.      Do the PHD2 calibrations while pointing in the recommended area of the sky.  That will be near the intersection of the celestial meridian and the celestial equator (Dec = 0).  I couldn’t follow your description of where you’re pointing the scope but it doesn’t sound right to me.

3.      Your mount probably has a huge amount of Dec backlash which you should manually clear before starting the calibration.  Once you’re pointing in the general sky position described above, start PHD2 looping then use the hand-controller to move the scope north (‘up’ button) until you see the stars moving in the PHD2 image display.  Then start the calibration without any further changes in scope position.

 

Your goal at this point should be to get a usable PHD2 calibration.  You can use the ‘Review calibration’ menu under ‘Tools’ to see the results of the calibration.  Until you can get a calibration that makes reasonable sense, there’s no point in trying to guide.

 

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

 

Good luck,

Bruce

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[Brian Valente]

Hi Kerry

In addition to Bruce's excellent feedback and advice, your digital drive system with ST-4 guiding works differently than most of the posts here since it's not a goto controller. Recap/adding to the prior comments:

- You want to use only one guide rate for calibration and guiding. 0.5x is probably best but you may need to experiment

- you will need to recalibrate guiding for each of your targets, and you would do this near the target. A Gemini system can do one calibration for any sky position, but your mount is not sky aware, so you have to re-do

- Bumping the mount north (as described by bruce) prior to calibration will help with your orthogonality issues. You should disable assume ortho = 0 and work to achieve a good calibration

Brian

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[Kerry Green]

Thanks for the suggestions.  I had heard that I needed to calibrate close to the target as well.  I am sure I have tried this in the past.  I have definitely missed the part about clearing the backlash.  I will give that a try, hopefully this evening if the weather holds.  I am just hoping I can resolve this issue.  It worked once before.

[Brian Valente]

Hi Kerry

>>>I am just hoping I can resolve this issue.

Do you have a specific issue? or just getting guiding going in general?

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[Kerry Green]

Nothing specific yet, just getting going.  I've got a lot of good things to try here, so I'm going to give them a shot.  I am thinking clearing the backlash should help a lot.  It is the one thing I have not yet done.

[Kerry Green]

I wanted to update everyone.  I seem to have solved my issues! Tonight has been the first night available to test, but so far, so good.  I deleted everything and started from scratch.  I am guiding at .5x, I cleared the DEC backlash, and calibration was flawless!  I calibrated near my target as recommended and all is well.  Currently imaging M81, M82.  The subs have nice star shapes.

[Bruce Waddington]

That’s great to hear, nice work!

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