I am struggling with autoguiding reliably and need help...I am doing something wrong I am sure.
I would be interested to hear advice around selecting guidestar magnitude/exposure - I have read that if the guidestar signal is SATURATED on the CCD you can get poor perfomance (clipping) so you must adjust exposure/gain to compensate, this may not be true for all centroid algorithms but certainly seems to upset Maxim EE this is made worse this $%^&ware selects the guidestar automatically form those in view (I think it picks the brightest! GRRR!). Is this correct?
Second is the rate of corrections to send to the mount 1s intervals seems to be a good start point and finally the slew speed - siderial or less, would you ever use more?
So much to learn and get right when you go beyond 30s at 1800mm...
I use an ST7E with built in guide chip so my set up is a little different, but here are my general settings for what it's worth.
I have the capability of being able to calibrate on any star on the guide chip, and the advice is not to saturate the guide star as it may cause false guiding corrections to be made.
I have read that 3s to 10s is the optimum guide star exposure range. Less than 3sec exposures can result in you “chasing the seeing”, more than 10s may not correct guide star excursions, resulting in trailing. I like to use 5 secs whenever I am able.
For focal lengths under say, 800mm, correcting at x1 sidereal rate is okay.
Imaging at 800mm to 2000mm, set the correction speed to x0.7
For over 2000mm I reduce corrections to x0.5 sidereal rate.
You are right – this is not easy but persevere and you will succeed as I understand that the Vixen Sphinx is a well engineered mount.
I personally find that I can “easily” auto guide at 1000mm and less; anything over tends to take a bit of tweaking and is not as straightforward.
I was going a little crazy - so many things to twiddle with and not sure which one to start with. The difference between my old setup and the new is the Orion StarShoot with Maxim s'ware vs LPI with GuideMaster. I thought this would be better but it seems to be worse - so far anyway.
But I am sure I have been saturating my guidestar and sending corrections to fast as well. I am going to have another go with the FR in and see how it goes. I really do not like the Maxim EE guid routines much - I really think you should be able to select the guidestar...
I use a ST7 also, on my LX200 (classic), using CCDSoft..
I've also read 3 to 10 second exposure time is optimum. Personally I find that if I get down to 0.5 second exposures with good brighness then I have a dramatic boost in image quality, I believe that it must start to keep up with some atmospheric distortions - but I am not sure.
If viewing conditions are very bad, I sometimes find longer exposures better.
I maximise the calibration distance, but it's usually still fairly short (about 7 seconds).
I disable DEC autoguiding in one direction, such that there is no complication of backlash in DEC. This is not a problem as the star only drifts in one direction in DEC, due to polar alignment error.
I usually give the images a pre-start delay of about 5 auto-guide exposures, allowing the autoguiding to settle down a little.
I use an aggresiveness of about 7 (out of 10) so it makes slightly less of a move than it otherwise would have, so it doesn't over comphensate and get confused.
Hmm, I can't think of anything else right now... Autoguiding certainly can take a bit to get right, especially if you are trying for RA and DEC in all directions and comphensating for backlash in either. I'd suggest starting with RA only.
I use a ST7 also, on my LX200 (classic), using CCDSoft..
I've also read 3 to 10 second exposure time is optimum. Personally I find that if I get down to 0.5 second exposures with good brighness then I have a dramatic boost in image quality, I believe that it must start to keep up with some atmospheric distortions - but I am not sure.
Roger.
Hi Roger
Hmm, sounds like you've almost got the ST7 behaving like an adaptive optics unit! I must give that a try (0.5 secs) with my set up and see how I fare. The fastest guide exposure I have previously used was 2 seconds and it seemed to work okay.
I also use maxim, and had a dreadfull time getting it right. As soon as it started, the guide star just moved off screen really fast.
I use it on my RCX, yet i could not get it to guide. After some mucking about, i found if it points east or west i also have to set or unset the meridian flip.
This should only be on German mounts and not fork mounts, but for some reason maxim needs to know which direction its facing. Try this first.
As for other settings, start with 5 as the Aggresivness, as it slowly moves the scope back if it drifts. Secondly i agree that you need to disable the DEC settings all together. I normally use anything from 1 second to 10 seconds exposure for my guiding.
1.5 second exposures
Agressivness 5 out of 10
.5 delay after correction
minimum movement .2 sec
maximum movement 1 sec
I have Dec activated....may try it turned off.
Seems to work well for me.
I always select the brightest guide star possible within reason....my guide camera is not anti blooming so obviuosly I will not select a star that has bloomed.
I still get a degree of movememt over longer exposures over 4 minutes....not sure if this is do with flex or polar align.
Hmm, sounds like you've almost got the ST7 behaving like an adaptive optics unit! I must give that a try (0.5 secs) with my set up and see how I fare. The fastest guide exposure I have previously used was 2 seconds and it seemed to work okay.
Is your ST7 parallel (like mine) or USB?
Cheers
Dennis
Sorry about the delay Dennis - was out observing in the country for the weekend.
My ST7 is a parallel one. That's about the only reason I have it - they had a sale of parallel ones a few (2?) years back and it was cheap Still Class1 and all that. I wish it was USB, would help the download times for full image wonderfully. But even then, it annoys me that SBIG still only use USB 1.1 not 2.
I agree it seems at that 0.5 sec range it appears to start behaving like a adaptive optics unit, but without understanding any of the technicalities or capabilities I don't see how that could be possible - surely it would remove or decrease the need for an AO7. There's lots I don't understand about the A07 though and hence the differences between adaptive optics as implemented with an AO7 and a fast correcting mount. Anyway, 0.5 sec or better I definitely notice an improvement in image quality so something is hapenning.
I really appreciate you sharing the wisdom - I wish I could get out to Kulnura one of these days and see how it is done by experts but my Saturdays are full to about 1800 every week, maybe in the school hoidays I can escape - my drift alignment and guiding sure could do with the help....
A near full moon has messed this image up - no flats etc applied just compression to get under 150Kb. But I do not care - this is a Canon full frame at iso100, 600s, NR on, at prime on the VC200L with FR so fl is approx 1200mm. Guiding with Orion Starshoot on the WO66 and Maxim EE software. Setting was agg 7 on X and Y with only -ve corrections applied to Y axis.
Polar alignment was via the iterative method.
I am happy with this result, I hope I can repeat it now....
Still Class1 and all that. I wish it was USB, would help the download times for full image wonderfully. But even then, it annoys me that SBIG still only use USB 1.1 not 2.
