Need some answers to some weird goings on....

SFn8CieR

Further to my 'weird goings on' Post a few months back, ZWO were unable or unwilling to find a solution to fix their problem with the ASIAIR Plus giving me weird guiding graphs on my Ioptron CEM70EC2 mount. Instead they blamed it on my not so perfect round stars (which are seriously good enough) and said it must be my mount etc...

Polar alignment is really good and the RA and DEC axes are well adjusted and I can take 2 to 3 min unguided pics most nights dependent on the seeing etc..

So take a look at my uploaded log from last night. In sessions 1 & 2 you can see the dec running nicely and the RA increasing in value with an rms error of 7.77 and 11.54. Yet my pics taken during these times are really good with very nice round stars.. Session 4 shows both axes guiding nicely for 1 and 3/4 hrs with rms=0.58. So its looking normal here.

phd2-guidelog-2024-10-12-201333.txt

762kB

Session 6 and 7 of the logs are also nice running at 0.7 rms..

I have tried to upload a pic taken at 11.05pm during the rising RA axis graph with rms=11.54 but an error on this forum wont let me. It is a 5 min guided pic and the stars look pretty good and round for an rms = 11.54. Something weird with ASIAIR and Ioptron mounts is going on. ZWO wont address it. Others with Ioptron mounts have had similar issues and no solutions from ZWO.

What is going on???

PMTeam@ZWO

SFn8CieR
Hello. We have carefully analyzed your guide log and made the following analysis and suggestions based on it:

According to the screenshot of the guide log calibration data you provided, there were significant deviations on the DEC axis observed during the intervals from 20:15 to 00:14. Conversely, the DEC axis calibration appeared normal during the intervals from 00:15 to 04:12. We speculate that an automatic meridian flip event occurred around 00:14. Given that your DEC guide mode was set to North, the DEC axis was able to correct itself normally after the flip. Therefore, we recommend setting the DEC guide mode to Auto to better adapt to such situations.

Additionally, in the guide calibration data from 20:15 to 22:15, the DEC axis deviated by approximately 30 arc seconds (30") over a period of two hours. This corresponds to an average deviation rate of about 30"/7200 seconds ≈ 0.004167 arc seconds per second. As a result, within the exposure time you set, the star points in a single-frame image appear nearly circular to the naked eye but may show slight elongation when examined with professional tools. To verify this, you can take the following steps:
Method 1: Stacking single frames
Stack all the single frames taken between 20:15 and 22:15. The stacked stars may shift in one direction
Method 2: Increase the exposure time
For this kind of guided deviation, set the exposure time to 5 to 10 minutes. The longer the exposure time, the more likely it is that even small deviations will accumulate to a level that is noticeable with the naked eye.

Hope this helps, thanks

SFn8CieR

PMTeam@ZWO
OK thank you, I will look further into this and will get back to you.
This does not however explain why the DEC axis is drifting upwards in Logs 1 and 2? It also does not explain why the ASIAIR shows such high rms values and yet my stars are nice and round. If my rms was as high as 11.54 then surely my stars would be very elongated, yet they are not? As I mentioned before, I can image unguided for 2 to 3 minutes with nice round stars, depending on the seeing conditions. So I take it my mount is good, but, the ASIAIR is giving false guiding information.
cheers.. Nick

PMTeam@ZWO

SFn8CieR This does not however explain why the DEC axis is drifting upwards in Logs 1 and 2?

According to your guide log, your DEC guide mode is set to "North". The DEC axis in log 1 and log 2 shifts in opposite directions, making it impossible to make effective corrections. Between log 2 and log 3, at 00:14, we speculate that a Meridian Flip occurred. After the Meridian Flip, the DEC axis can be corrected correctly in "North" mode.

SFn8CieR It also does not explain why the ASIAIR shows such high rms values and yet my stars are nice and round. If my rms was as high as 11.54 then surely my stars would be very elongated, yet they are not?

In log 2, your RMS value is 11.54 '', but this is the cumulative result over a period of time (from 22:19 to 00:14), not the RMS value when you actually took a single frame. Based on the exposure time you provided, we intercepted the data from 22:51 to 22:54 as a single frame simulation. As can be seen from the figure below, the RMS value of a single frame is 1.76 ''. The error of this single frame is small, making the stars appear more rounded when observed with the naked eye.

SFn8CieR OK I have done asked you asked to stack my images between 20.15 and 22.15 and the average radius is 0.838, so there is a slight amount of out of roundness of the stars but not enough to coincide with the massive dec movement on the graphs. I dont think anyone gets perfect round stars when guiding so it still does not make any sense.

Thank you for stacking the images from 20:15 to 22:15. You can zoom in on the stacked images to see if the stars are all shifted in the same direction.

SFn8CieR

OK I have done asked you asked to stack my images between 20.15 and 22.15 and the average radius is 0.838, so there is a slight amount of out of roundness of the stars but not enough to coincide with the massive dec movement on the graphs. I dont think anyone gets perfect round stars when guiding so it still does not make any sense.
Why is the ASIAIR showing huge DEC movements during guiding sometimes and not others?
I have previously tried using AUTO on DEC Corrections and it stopped giving DEC corrections for some periods of time and when the dec graph crossed over the centre it started showing corrections again.
This is so confusing and I am thinking that the asiair is not showing what is going on accurately.
As I mentioned my mount can take 2 to 3 min pics without guiding with very good stars, depending on the seeing.
Is there a problem with the ASIAIR and Ioptron mounts? Some others have the same problem too.
Can you ask your software developers to look into this please.
thanks..
PS. I tried to upload a pic to show you but an error keeps coming up......oops something went wrong? What is the problem here?

SFn8CieR

Hi, thanks for the response.
What do you mean by "According to your guide log, your DEC guide mode is set to "North". The DEC axis in log 1 and log 2 shifts in opposite directions, making it impossible to make effective corrections."?? Please explain further. Are you saying the drift is caused by the DEC set to North? Should I always have it set to Auto to prevent this drift?

OK so the rms of a single frame is 1.76", yes that makes more sense. Still this is very high as I try to keep it below 1".

Shouldn't the Asiair change the DEC setting automatically before and after, a meridian flip or does it only do that when it is set to Auto? Example.. So if it is set at North say before a meridian flip, then after the flip it should automatically change it to South?

Thank you for taking the time to look at my graphs and explain. I will try again on a clear night, when we get one, to see if I get DEC drift again if set to North and then change it to Auto to see if it corrects it.

cheers Nick

retman

You may wish to read the PhD2 manual section on unidirectional guiding. My understanding is that "north only" or "south only" are for cases where your mount has large backlash issues. Guiding in only one direction cannot control the axis in both directions. I have always guided in "auto" mode and had good success.

SFn8CieR

retman
My mount should not have large backlash issues, but I am not certain. Its an Ioptron CEM70EC2 so it should be good. Do you know how I can check this? When I calibrate either on the east or west side of the meridian It gets there in 12 steps so the backlash should be good??? If I calibrate on the east say around 30 deg and then go to a target on the west side, I always flip the guiding and it is usually good. Sometimes if the guiding is not so good, I put the DEC into North and try that and use it if the rms gets better. This has been the case lately. I understand that the mount cannot guide both axes in this mode.
What mount are you using?
cheers..

retman

SFn8CieR i currently use an am3 but also have a star adventurer gti. I tried unidirectional guiding with the sa gti and had terrible drifting issues. Went back to auto and it was much improved.

SFn8CieR

retman
Very different mounts but the guiding inputs should be the same. Will try what you said. thanks..