|
Long focal length imaging will show up deficiences in your Polar Alignment and balance more than shorter focal length. It will also be more sensitive to seeing.
At the end of the day round stars are what you are after and you got that so there is no problem.
Here is what I use:
MMOAG, STi guider, 2935mm focal length or so.
Guide exposures - I vary this depending on seeing. The worse the seeing the longer but no longer than 4-5 seconds. Also depends on the brightest guide star available. I use autodark so the guiding doesn't pick a hot pixel by mistake over the guide star.
Usually I use 2 maybe 3 second guide exposure and sometimes 1 second if a bright guide star. I find the guide star can affect guiding quite a bit so if I see bad errors my first action is to try another guide star.
Callibration with a PME is really fast. I use about 30 pixels travel and it takes about 20 seconds to do a callibration run.
Aggressiveness is usually about 7 to 10. If it is jumping around too much I set it a bit lower.
Min move .1 Max move 1. I don't want corrections over 1 as usually that is seeing or PE not actual drift.
I use PEC and this usually seems to increase the errors but it is really adding or subtracting the PE curve to the corrections needed so you may see larger errors but its actually more accurate and you get rounder stars.
I don't see you have a problem here as your stars are nice and round.
You can always get a bit better by improving the polar alignment with T-Point, checking your balance, making sure everything is tight and no flex etc etc.
MMOAG in theory would do no better than self guiding as they are both guiding through the scope. The only advantage of MMOAG is you can use a more upspec guide sensor ( the ST237 chip is pretty noisy and low res but it works) and you can guide narrowband images. Its also a bit easier to guide blue exposures which can be dull for guide stars. Otherwise self guide is great and I wish I had it on my FLI sometimes. Although I like the new SBIG filter wheel guide camera. I wonder if that filter wheel would work with a FLI camera? FLI filter wheels are very expensive (AUD$2200 including shipping and GST).
I find guide errors with my CDK17, STi and PME with PEC running at around .2 to 1.3 error size. When its running nicely with decent seeing it will be around .1 to about .6. I think I can get that a tad lower with an even better PA and more t-point model runs.
Greg.
|