PHD guiding and how to tell if polar alignment is OK

[alcol620]

Hi

I am relatively new to PHD and took the plunge last week to use it for drift aligning after my Jason Dale polar alignment.

It seems to work and the trens lines on the PHD graph are relatively near the x axis.

What are the parameters to look at to judge the accuracy of the guiding? Is it simply the RA and DEC RMS values or should I be looking at something else?

[jarbi]

Hi,

It also depends which version of PHD You are using, but basically you need to look at the DEC guiding graph. 

In PHD 1.x I think the only way is to look at the direction of the correction pulses in DEC. When it is always the same direction, it shows that PHD is compensating a DEC drift, so your polar alignment is a bit off. When it oscillates above and under the middle line on the graph, you have most probably good polar alignment.

If your alignment is way off, you can see that the DEC guiding can not keep up with the drift: the DEC graph "runs away" from the central line.

In version PHD 2 you have an option "show target", that displays the recent positions of the guidestar relative to the centrum of the green circle. With good polar alignment you have random "scores" in every direction. With polar alignment slightly off it will show more hits in a specific quadrant of the "target" scoreboard.

Clear skies,

Janos

[alcol620]

Thanks Janos

I will look at this when outside later. i think I have PDH2 as I can view a "target" map.

When the guiding starts the RMS values of DEC and RA are indicated, I assume that these indicate the amount that the amount is being moved around the axis. Is this correct. The smaller the value, the smaller the amount of guiding/adjustment required????

Regards

Alec

[griz11]

Turn on logging and get a copy of PHDlab its a free piece of software for analyzing the PHD logs. This will give you the error on polar alignment and many other things. You can have it read the log file live if you want as well. http://countingoldphotons.com/phdlab-intro/  Gives you a lot more info than PHD does. Works well together I've been using it for a couple of months now with no problems.

Guider plot screen

Main page with floating guider plot.

Griz

[griz11]

The first example shows not so good guiding performance and the second good performance but misalignment to the pole as the other poster suggested. Note they are close to the center but offset to one side.

Griz

[alcol620]

Thanks Griz

Most helpful

Regards

Alec