whzzz28
13-07-2012, 10:35 AM
It's been a miserable wet week in Brisbane, and with some slow work days ive been mulling over my previous three outings with the new lodestar.
I recently purchased an SX lodestar to replace my QHY5.
I've been following the same procedures i did with my QHY5 for drift aligning (with PHD) and general guiding.
It has been working but with quirkes. So now i am trying to get to the bottom of it.
In my last night out it took me an hour just to get PHD to calibrate (without polar alignment). My normal procedure is to get the mount as accuratly aligned as i can (compass with 11degrees to the west for true south, digital inclonometer for altitude). I then move the scope manually, slightly to the west (below 30degrees from horizon). Turn on sidereal tracking and then fire up PHD. Find a brightish star and start calibration.
Once calibration is done i turn off DEC guiding and then begin drift aligning to get azimuth aligned. I never touch altitude as the scope is always in the same place and i have already calibrated that.
The problem i have been having since using the lodestar is the "Star did not move enough" during calibration.
I find this weird because if i grab a shot, then wait 10sec~ or so and take another, i can clearly see the stars move, quite a bit!
RA goes up to 60 steps with a movement rate of under 25 (thus the error). Normally at 60 steps it is somewhere between 20-25. This is with a step size of 2200ms.
The obvious thing to do is increase step size in PHD, however i had it increased to 7000ms before it moved enough, and even then it took ~50 steps. This seems way too much to me.
Maybe it was just too close to the meridian, so i just moved the scope out to a patch of stars due west. Left the step size at 7000ms and then tried calibration again. It took 25~ steps to calibrate even at 7000ms out here... That can't be right, the QHY5 only took 20~ steps at 2200ms, even near the meridian.
Even when i did finally get it calibrated, moved it back close to the meridian and turned off DEC guiding; i had issues with drift alignment. The "north/south" i mention below is in relation to the PHD graph.
The star drifts north - great ill ajust the knobs... Try again, still drift north by a lot - ok again, adjust the knobs.
Now its drifting to the south. Ok ive gone too far.
Eventually it got to the point that i was adjusting the knobs by a hair of an amount and the star was drifting north/south depending on which way i adjusted it.
Eventually i got tired of the backwards and forwards and simply left it at what i thought was decent. I think it was pretty close as i didn't have any (or little) drift in my images, but i have no idea why the PHD graph was accelerating north or south very fast if it was aligned. Normally it flattens out when you are near perfect. I think it has to do with the calibration data i took, and since it was now near the meridian, it wasn't accurate.
So thats the first problem i have been having. Why do my step sizes need to be so high with the lodestar?
The next i am not so sure it is a problem, but i can't find any help or ideas as to what is causing it or what it is.
Once i get the whole rig going and want to start imaging, i calibrate (and apart from taking a long time, it does calibrate) and start tracking.
The last night out, the tracking graph was the best i had ever seen. The RMS was less than 0.1 and OSC less than .3.
Everything appeared to be humming along.
However i noticed PHD flashing every now and then as it does when it loses the guide star. I turned on audio and noticed that at least once every 1min, PHD will beep (sometimes twice in a row) and the DEC line will flatline (0) before picking back up again. The night was cloudless, and i could see the star in PHD clearly.
It doesn't appear to be causing any issues in terms of guiding, but i am wondering why it is doing this. There is nothing in the logs, no notes or anything. Is this because the star did not move (enough) in the DEC axis, so PHD complained thinking that it was a problem?
Or is this a notification that the DEC axis is not responding to commands after PHD issues them?
Could it be an issue with the camera not taking a shot?
Before my last outing i pulled apart the HEQ5 and added some washers to the transfer gears to try and remove the gear rattle as the mount speeds up, and also to reduce backlash in the gears (and re-grease them). There is still some rattle, but it is mostly gone now, however i did find some backlash with the gear setup so i moved them (oh so slightly) closer which reduced it. I also tightend the worm gear as there was a bit of slop in both the RA and DEC. RA is now tight (but not binding), DEC still has some slop that i can't remove with tightening for some reason, but it is only slight and i don't think it is causing any issues.
I am wondering if maybe i have done something that is causing problems. DEC and RA doesn't appear to be binding, the mount runs fine and i can turn the gears with my finger.
Maybe this is all normal for the lodestar, but there is such a difference between it and the QHY5 when it comes to setting up; it was a little unexpected. I know it is much more sensitive (which is why i bought it), but didn't think it would make calibrations harder (if anything, easier).
Some details:
Guidescope: Meade 5000 (80mm, f/6) or Orion ST80 (if i am using the Meade)
Focus was as perfect as i could get it, but i didn't run any focusing procedures i just turned the camer on and adjusted until they became pinpoints. Stars do appear as square pixels on the lodestar though, and sometimes stars appear as a slight column (1x2 rather than 1x1 or 2x2), which i put down to being the camera design or something, where as on the QHY5, most stars appear to be slightly fuzzy. Then again i used the QHY5 mostly through the ST80, which is a very basic (and rather terrible) scope. The lodestar has been on the Meade pretty much exclusively.
Ive played with almost all PHD settings to see what works and what doesn't.
Different exposure times cause PHD to beep more or less.
0.5sec exposures cause it to beep less, 1 sec exposures cause it to beep more and 2sec exposures, oddly enough causes it to beep less.
Things i most often fiddle with:
Max Dec Duration: I don't know why, but sometimes, randomly my DEC just starts climbing. It was tracking great for the past hour then it just decides that DEC will slowly climb and climb until it goes off the graph. Sometimes after a few mins, it fixes itself and slowly comes back down to normal... it's rather freaky and there isn't any noticeable elongation of stars during the process. I found changing Max dec duration will remove this, but you need to wait for it to occur before you know if you need to increase it or not.
RA Aggressivness: I use between 100 and 120. Some nights i find 100 isn't enough, other nights i find 100 is almost too much, guessing that is a polar alignment issue or just the HEQ5?
Calibration step size: I never used to change it but find i need to change it every night with the lodestar, normally to very large values to get it to calibrate.
Sorry for the long post, i'm just trying to understand what is going on, and try and reduce my setup times. Spending an hour just trying to calibrate PHD is not something i want to do every night.
I might try alignmaster sometime, but my FOV from my backyard is a bit limited.
Actually for a while i thought maybe my polar alignment is so exact that guiding was so insignificant that PHD had little to do.
So i did a test, with a 5min exposure there was elongation of stars, so the alignment/mount obviously wasn't that great.
PS: No, i wasn't trying to guide on a bright pixel. Been there, done that, got red faced before and will never fall for it again :)
Any comments, suggestions or thoughts are welcomed.
Thanks.
I recently purchased an SX lodestar to replace my QHY5.
I've been following the same procedures i did with my QHY5 for drift aligning (with PHD) and general guiding.
It has been working but with quirkes. So now i am trying to get to the bottom of it.
In my last night out it took me an hour just to get PHD to calibrate (without polar alignment). My normal procedure is to get the mount as accuratly aligned as i can (compass with 11degrees to the west for true south, digital inclonometer for altitude). I then move the scope manually, slightly to the west (below 30degrees from horizon). Turn on sidereal tracking and then fire up PHD. Find a brightish star and start calibration.
Once calibration is done i turn off DEC guiding and then begin drift aligning to get azimuth aligned. I never touch altitude as the scope is always in the same place and i have already calibrated that.
The problem i have been having since using the lodestar is the "Star did not move enough" during calibration.
I find this weird because if i grab a shot, then wait 10sec~ or so and take another, i can clearly see the stars move, quite a bit!
RA goes up to 60 steps with a movement rate of under 25 (thus the error). Normally at 60 steps it is somewhere between 20-25. This is with a step size of 2200ms.
The obvious thing to do is increase step size in PHD, however i had it increased to 7000ms before it moved enough, and even then it took ~50 steps. This seems way too much to me.
Maybe it was just too close to the meridian, so i just moved the scope out to a patch of stars due west. Left the step size at 7000ms and then tried calibration again. It took 25~ steps to calibrate even at 7000ms out here... That can't be right, the QHY5 only took 20~ steps at 2200ms, even near the meridian.
Even when i did finally get it calibrated, moved it back close to the meridian and turned off DEC guiding; i had issues with drift alignment. The "north/south" i mention below is in relation to the PHD graph.
The star drifts north - great ill ajust the knobs... Try again, still drift north by a lot - ok again, adjust the knobs.
Now its drifting to the south. Ok ive gone too far.
Eventually it got to the point that i was adjusting the knobs by a hair of an amount and the star was drifting north/south depending on which way i adjusted it.
Eventually i got tired of the backwards and forwards and simply left it at what i thought was decent. I think it was pretty close as i didn't have any (or little) drift in my images, but i have no idea why the PHD graph was accelerating north or south very fast if it was aligned. Normally it flattens out when you are near perfect. I think it has to do with the calibration data i took, and since it was now near the meridian, it wasn't accurate.
So thats the first problem i have been having. Why do my step sizes need to be so high with the lodestar?
The next i am not so sure it is a problem, but i can't find any help or ideas as to what is causing it or what it is.
Once i get the whole rig going and want to start imaging, i calibrate (and apart from taking a long time, it does calibrate) and start tracking.
The last night out, the tracking graph was the best i had ever seen. The RMS was less than 0.1 and OSC less than .3.
Everything appeared to be humming along.
However i noticed PHD flashing every now and then as it does when it loses the guide star. I turned on audio and noticed that at least once every 1min, PHD will beep (sometimes twice in a row) and the DEC line will flatline (0) before picking back up again. The night was cloudless, and i could see the star in PHD clearly.
It doesn't appear to be causing any issues in terms of guiding, but i am wondering why it is doing this. There is nothing in the logs, no notes or anything. Is this because the star did not move (enough) in the DEC axis, so PHD complained thinking that it was a problem?
Or is this a notification that the DEC axis is not responding to commands after PHD issues them?
Could it be an issue with the camera not taking a shot?
Before my last outing i pulled apart the HEQ5 and added some washers to the transfer gears to try and remove the gear rattle as the mount speeds up, and also to reduce backlash in the gears (and re-grease them). There is still some rattle, but it is mostly gone now, however i did find some backlash with the gear setup so i moved them (oh so slightly) closer which reduced it. I also tightend the worm gear as there was a bit of slop in both the RA and DEC. RA is now tight (but not binding), DEC still has some slop that i can't remove with tightening for some reason, but it is only slight and i don't think it is causing any issues.
I am wondering if maybe i have done something that is causing problems. DEC and RA doesn't appear to be binding, the mount runs fine and i can turn the gears with my finger.
Maybe this is all normal for the lodestar, but there is such a difference between it and the QHY5 when it comes to setting up; it was a little unexpected. I know it is much more sensitive (which is why i bought it), but didn't think it would make calibrations harder (if anything, easier).
Some details:
Guidescope: Meade 5000 (80mm, f/6) or Orion ST80 (if i am using the Meade)
Focus was as perfect as i could get it, but i didn't run any focusing procedures i just turned the camer on and adjusted until they became pinpoints. Stars do appear as square pixels on the lodestar though, and sometimes stars appear as a slight column (1x2 rather than 1x1 or 2x2), which i put down to being the camera design or something, where as on the QHY5, most stars appear to be slightly fuzzy. Then again i used the QHY5 mostly through the ST80, which is a very basic (and rather terrible) scope. The lodestar has been on the Meade pretty much exclusively.
Ive played with almost all PHD settings to see what works and what doesn't.
Different exposure times cause PHD to beep more or less.
0.5sec exposures cause it to beep less, 1 sec exposures cause it to beep more and 2sec exposures, oddly enough causes it to beep less.
Things i most often fiddle with:
Max Dec Duration: I don't know why, but sometimes, randomly my DEC just starts climbing. It was tracking great for the past hour then it just decides that DEC will slowly climb and climb until it goes off the graph. Sometimes after a few mins, it fixes itself and slowly comes back down to normal... it's rather freaky and there isn't any noticeable elongation of stars during the process. I found changing Max dec duration will remove this, but you need to wait for it to occur before you know if you need to increase it or not.
RA Aggressivness: I use between 100 and 120. Some nights i find 100 isn't enough, other nights i find 100 is almost too much, guessing that is a polar alignment issue or just the HEQ5?
Calibration step size: I never used to change it but find i need to change it every night with the lodestar, normally to very large values to get it to calibrate.
Sorry for the long post, i'm just trying to understand what is going on, and try and reduce my setup times. Spending an hour just trying to calibrate PHD is not something i want to do every night.
I might try alignmaster sometime, but my FOV from my backyard is a bit limited.
Actually for a while i thought maybe my polar alignment is so exact that guiding was so insignificant that PHD had little to do.
So i did a test, with a 5min exposure there was elongation of stars, so the alignment/mount obviously wasn't that great.
PS: No, i wasn't trying to guide on a bright pixel. Been there, done that, got red faced before and will never fall for it again :)
Any comments, suggestions or thoughts are welcomed.
Thanks.