ShutterChronicles Você esta em SP?
Meu whats é 11-996530585. Abraços

Hello folks!

I got my AM5 over a month ago and unfortunately haven't had good weather to test the mount.

I'll show you my test report here. What do the test values of my AM5 say?

Should I use the default values in the ASIair+ for the first test or would you adjust the parameters?

CS Gernot

Gernot What do the test values of my AM5 say?

Even though the peak-to-peak periodic error is low (about 8 arcsec peak-to-peak), the segment in the bottom graph shows a very pronounced 4th harmonic term.

By eyeballing it, the 4th harmonic has a worst case amplitude of perhaps 4 arcsec peak-to-peak. That will cause the periodic error curve's slope be the equivalent to a 4x4 arcsecond peak-to-peak (16 arcsec peak-to-peak) compared to a mount that has no harmonics.

I suspect that the mount would behave like a good 16 arcsec p-p mount, at what appears to be a 288 second period. Thus about guiding smoothness of a 24 arcsec peak-to-peak mount that has a 430 second period (the original poster of this thread).

The result is probably about the same, or a little worse, than the original poster (1st post) in this thread.

By carefully tuning the guide parameters, you should be able to autoguide the mount to somewhere between 0.4" total RMS and 0.6" total RMS (if the declination axis behaves similarly).

Should I use the default values in the ASIair+ for the first test

I suspect that if you use the ASIAIR's default, you might be able to get between 0.7" and 1.4" total RMS, and at times have short term sudden larger excursions. By the way, if the total time for the short term large excursions sum up to be much shorter than your total exposure time, they do not really hurt -- it depends on how often you get those spikes.

FWIW, your mount has the strongest 4th harmonic than any mount that we have seen here so far. It would be interesting to see what results you get, especially with the ASIAIR's default. Every strain wave geared mount is very different from another one -- so much so that it is like guiding a mount from a totally different manufacturer.

Chen

w7ay

Hello Chen

Thank you for your effort and the detailed answer. I'll run the first session with the default settings and report back here. How long should I run the test?
How would you rate my copy on paper? Good - Ok - Bad ?

CS Gernot

Gernot How long should I run the test?

At least a few hours. If you notice, on that second chart on your piece of paper that the first 288 seconds is already very different from the middle third, and again different from the last 288 seconds.

How would you rate my copy on paper? Good - Ok - Bad ?

Hard to tell. The large 4th harmonic is concerning. And I cannot compare with anything that I have; my two strain wave gear mounts are from a different manufacturer.

Chen

w7ay hi Chen, I am trying to figure out why my mount does not seem to be responsive to any duration change or exposure length change. I still get the randon 2” spike in RA but my guiding is always near 0.7rms no matter what I do to try to improve it. If I run at 1s at 500ms on dec and ra at 40% aggression I can change it to 80ms and absolutely no difference. I can run at 0.5s up to 3s and always the same 0.7 to 0.8 rms. Asiair always just picks 6-8 stars, unsaturated but not very sharp stars in the box. I am starting to think that maybe it is my guide scope sharpness that may be contributing to the inability for the program to guide better. My slope was 0.16 so fairly good for zwo.
Even bumping things up to 0.5s gets me the same sawtooth pattern 0.7 average rms with 100ms pulses. Any thoughts? Thanks. I would like to smooth out my graph and try for 0.5 average. All my calibrations are within 30 degrees of the meridian and i using my 290mm mini on a 50mm f3.2 guide scope. It has got me baffled why it still seems jagged even with 100mm pulses and less. Better guide scope needed or do my calibrations on target rather than near the meridian? Right now it seems that nothing really improves my guiding. I do not expect miracles but it would be nice to figure out the weakest link! TIA.

Kevin_A If I run at 1s at 500ms on dec and ra at 40% aggression I can change it to 80ms and absolutely no difference.

Hi Kevin, remember that the 80ms number is the max duration of a pulse. If the autoguider never asked for more than 40ms (for example), then setting it to 80ms or 2000ms will not change anything, since there is nothing to limit in that case.

I can run at 0.5s up to 3s and always the same 0.7 to 0.8 rms.

Yeah, this is the weird part.

With the rapid changes in the periodic error (i.e., large slopes caused by the higher harmonics), the error should improve from the 0.7" down to the 0.3" to 0.4" range that your mount should be capable of.

A 3 second guide exposure would allow your 0.16" slope to move by 0.16 x 3 arc seconds before any correction is issued, or around 0.5 arc seconds; and that is just for the RA axis.

If the declination axis has the same amount (but independent) of 0.5" RMS error, then the total would come to be 0.707" total RMS... (RMS is the square root of the sum of squares), or close to what you are seeing.

Lopping that exposure time down to 1 second should have limited the excursion from 0.5" down to 0.16", and make the error be limited by other things than the mount's PE itself.

The fact that you are not seeing an improvement points to something else being the "tallest tent pole." I.e., something else is causing a 0.5" type error (in the RA axis) so that shortening the exposure time did not improve anything.

Asiair always just picks 6-8 stars, unsaturated but not very sharp stars in the box.

And that may be the problem.

Remember that some time back, I had shown a number of bar graphs showing the "typical" SNR distribution of stars. The ASIAIR uses SNR as a weight to determine the average centroid. And, given 6 stars, it is probably just the equivalent of using the uniformly weighted centroid of only 2 stars. I.e., you are getting very little improvement from multiple stars, and that could be the "tallest tent pole."

On an ASIAIR with a 55mm aperture guide scope at 200mm focal length (f/3.6) and an ASI178MM at a gain of 250 (analog gain of 25 dB) and an exposure time of 0.5 seconds, I can consistently get 12 stars from it, even in the star starved region around M81/M82 where I was playing around last week when clouds were thinner.

Notice a couple of things in this choice. The guide scope is actually a Borg 55FL with its reducer, chosen to give me a large aperture (and flat enough to cover the camera). The ASI178MM was chosen to give me a large FOV (if all else is equal, the larger FOV means more stars to pick from). The camera gain is pushed enough so that singularly bright stars will saturate, and causes the one or two bright stars to not get included in the centroid average (otherwise the SNR weighting will reduce to just using that single one or two bright star for guiding).

So, I would recommend tuning your guide system so that you can get all 12 stars that ASIAIR will process (the most the ASIAIR will use; guide systems like DONUTS will use all stars in the FOV that it can see, and DONUTS also uses uniform weighting instead of SNR weighting).

If the centroid measurement is coarse, then you are limited by centroid measurements, not by the feedback loop.

Check too that your stars are not distorted towards the edge of the field. I don't think that is your primary problem, but it can be as you tune the guide system.

You may have been too timid with pushing up the gain to get the stars. Don't be. With the short exposure times (i.e., shorter than 10 seconds), you can pump the gain up quite a bit before the dark noise dominates over the read noise.

After you have the guide scope tuned to consistently get 12 stars (while ignoring saturated stars) the next thing to do is to reduce the guide rate to 0.25x sidereal on ASIAIR (the ASIAIR will not let you go below that). It was a serendipitous discovery when looking at the sawtooth graph, but so far has served me well since I started using it.

By the way Kevin, on a different topic, I took my own advice about drilling the EAF to keep it from falling below the declination plate for both my FSQ-85 (first image) and my FOA-60Q EAFs (second image).

So, I have at least 4 EAFs now that are mounted this "direct mounting" way.

Chen

Kevin_A Hi Kevin, maybe it's listed in an earlier post, but what guide camera are you using? My ASI178 consistently grabs 10 to 12 stars (using the AA+), as long as there are that many to choose from in my FOV. MY ASI120 rarely captured more than 6.

Edit: I get the same random spikes that you are describing. Regardless of duration, aggression, etc. They generally come and go within 2 frames of guiding, and since my rig has been working well, I see no detectable affect in my images.

Kevin_A Best I know, 0.5 is the only available guide rate using the ASIAir. However, maybe the newly released firmware has changed that. Not sure. See item 5 below.

"From V1.1.2 to V1.3.0, we made these changes:
1.adding meridian settings
2.adding altitude limits
3.adding a fixed park position
4.optimizing cable winding problem in the Alt/Az mode
5.memorizing custom guide rate
6.fixing DST/LST misunderstanding
7.fixing problem that track light off after GOTO
8.adding multi star alignment (differ from polynomical optimization )
9.fixing other bugs"

Edit: If using a PC, guide rates are adjustable.

KC_Astro_Mutt Best I know, 0.5 is the only available guide rate using the ASIAir.

FWIW, this is what my mount shows:

The command protocol of the RST-135 has a resolution of 0.01x sidereal rates, but the ASIAIR limits the guide rates to four values: 0.25, 0.5, 0.75 and 0.9x. Problem as usual with ZWO crippling the better equipment the ASIAIR connects to. I don't know why it does not allow the user to select what they want, instead of the limited knowledge of ZWO's coders on what good guiding requires.

Chen