help out now guiding whats going on?

[Daniel-K]

out now in the obsy and i cant seem to get the guiding working properly this is the best i can do, can any one help

thanks

Dan

[Ewan]

Dan that graph looks really flat compared to mine tonight & im managing (what seems like anyway) pretty good data & round stars or am i missing something in your pic ?

[tonedeaf]

the graph looks good!

btw guiding is perfect as long as the result (image) is filled with pointy stars

[IanL]

It looks about as perfect as you can get to me. The two figures at the left are helpful:

1) RMS is the root mean square of the average distance (in pixels) of the guidestar from the lock point. The average is calculated for the number of guiding steps currently shown on the graph (100 in this case) and applies to RA guiding only (blue line). So in your case over the past 100 steps the guide star has been an average 0.09 pixels off the lock point in RA.

If you know the focal length of your guider (in mm) and the size of your guide camera pixels (in um), use this calculator (http://www.wilmslowa...tm#ARCSEC/PIXEL) to work out your guider pixel scale. Multiply the result by 0.09 and you will then know how precise your guiding in RA is in arcseconds.

2) The OSC index is the probability that guiding will change direction at the next step (i.e. the blue line will cross the centre of the graph). In your case it is 19%. There isn't a hard and fast rule about this one; if you have a small RMS a large OSC index is not an issue; but if you had a large RMS figure and a large OSC index, that would tend to suggest the poor guiding is due to lack of stability in the setup (could be mechanical/balance problems, wrong exposure/gain on the camera or just really bad seeing conditions).

[Zakalwe]

Are you using a finderguider? With a short focal length the graph can be very flat. The graph is not a bad indication, but the litmus test is the sharpness of the stars.

Also, IIRC Craig Starkey reckons that the OSC should be about 0.3

[ollypenrice]

That's a good graph. Even if your guidescope FL were short and your guide pixels large that should be good enough to keep a decent FL imaging scope sub pixel in error.

If your stars aren't tight and shapely you must have flexure.

Olly

[Daniel-K]

sorry should have mentioned with a finder guider. why does it split in the middle?

[Ewan]

I don't think the two lines will overlay one another exactly, ever, unless you have nicked some bits from NASA :-), you would need perfect PA and a miracle to get a combined one line, that's my thought anyway but i could be wrong.

[russellhq]

If you download PHDLab (free), you can input your guide scope FL & guide cam pixel size and then you can graph the error in arcsec/pixel over time.This provides much more useful info than the PHD graph.

http://countingoldphotons.com/phdlab-intro/

You can also run it during a live guiding session as well.