PHD2 Multi Star Guiding - weird graph

[stevepsheehan]

Morning all.

I tried the new MSG option in the Dev3 version of PHD2 last night, and was VERY impressed indeed! About 50% cloud, and 5 minute subs would have sunk an earlier version I suspect, but the MSG option seemed to take it in its stride, with nice round stars in nearly all my subs. Graph was weird though, with the red, Dec plot being displaced by a large amount. With reported RMS Tot figure of 0.28px, 1.24", I'm guessing this can't be genuine, and is possibly a glitch in the Dev3 version? Any thoughts?

Cheers,

Steve

 

Edited January 26, 2021 by stevepsheehan
clarification of scale

[teoria_del_big_bang]

Steve,

I too got my first chance to try this on Monday and very impressed.

I did not think too much how it really worked though as it seems to pick several stars but use one for guiding rather than averaging all the ones picked, so I assumed it just swapped to guide from one of the other picked stars if it lost the guide star. But that was my assumption as it puts markers around several stars but then highlights one of them. So this assumption could be wrong.

Steve

[david_taurus83]

The graph indicates that the guide star is off centre slightly on the Dec axis but the corrections are keeping it in place. What you don't want is it bouncing back and forth. Some mounts have excessive backlash and its recommended to guide Dec in one direction only, which would show a similar graph to yours. As you say though, stars are round so that's what matters. Might be worth checking balance and polar alignment next time out.

[newbie alert]

PA,  DEC is slightly rising and RA is the opposite side of the trend

[knobby]

Looks like the Dec wasn't actually responding to guide commands ? Too low aggression setting  ?

[TerryMcK]

I wouldn't worry too much about the graph. As you said that you were getting nice round stars then that is evidence enough. I've used the multi star guiding a few times and it is really good.

[newbie alert]

1 hour ago, newbie alert said:

PA,  DEC is slightly rising and RA is the opposite side of the trend

Sorry your RA is fine

[kens]

@stevepsheehanCan you attach the guide log? The Help menu is the place to look for them

[stevepsheehan]

Thanks for the comments all.

Re the PA, it's all mounted on a pier, and was accurate to 6" (according to Sharpcap), when I set it up in December, but I will check it again. 

Re the aggressivness, the mount has been hypertuned by Darkframe, and their recommendation was to lower it, rather than increase it, but again, I'll give that a try.

As has been said though, the goal is round stars, and I have those, so no big deal really. I'll let you know how it goes.

Steve

[stevepsheehan]

13 hours ago, kens said:

@stevepsheehanCan you attach the guide log? The Help menu is the place to look for them

I think it's this one:

PHD2_GuideLog_2021-01-25_150221.txt

[kens]

It looks like the mount is not responding to dec guide commands in either direction until its a big correction. Then it overshoots.

That would be a mechanical issue, most likely.

You've got a lot of huge spikes, especially in RA that look like the scope is being bumped. Did you lose many subs?

 

[stevepsheehan]

No losses at all, other than due to cloud. This is a very quick stack and stretch, and zoomed right in; like I said, I was shooting through hazy cloud, so focus is a bit iffy, but I'm happy wih the star shapes:

 

Edited January 28, 2021 by stevepsheehan
adding pic