Whats your "Max & Min Periodic Error" in your AM5 test report? - Forums

Topic starter

Oct 20, 2023 · Edited: Oct 20, 2023

Hi.

I was wondering what your "AM5 Periodic Error Test Report" says about your AM5s "Max & Min Periodic Error" - and what your general RMS error is when you're out under the stars guiding.

I think it would be interesting to know much the "Max & Min Periodic Error" affects our guiding.

I'll start:

Scope
Redcat 51 (focal length: 250mm)

Max & Min Periodic Error
26.8 / 15.9 Arc-secs

General RMS error (using a ASIAIR PLUS)
~0.3

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Ashraf AbuSara

Oct 20, 2023 · Edited: Oct 21, 2023

I don't think there is a direct correlation between PE and tracking error as much as it is the steepness of the slope of your PE. The steeper the slope, the more corrections your mount has to make quickly and the harder it is to maintain a low RMS error. Also there are numerous confounding factors that can significantly affect tracking error with harmonic mounts. Setting the right aggression, correction period, guided exposure rates etc is important. Additionally Harmonic drives in general and AM5 in particular is very seeing dependent. So if you live in an area with poor seeing your guiding maybe significantly worse than an area with generally good seeing, no matter how good the version of the AM5 you got.

I have learned to ignore the test report. I think it is not very useful to draw any conclusions. I currently operate a C11 at a FL of 2065mm with a 0.7x Starziona LF reducer with the AM5 mounted on the TC40 tripod and depending on the location of the target and seeing conditions my RMS error can range from just below 0.3" to 0.6" even in mild breeze. Targets closer to the celestial equator are more difficult to track so I tend to get 0.5-0.6", but anywhere around Polaris can easily track 0.3" all night long.

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Tom Carrico

Oct 21, 2023

I cannot find my report, but I recall my AM5 that I bought December 2022 had an error of about +20/-16". I use a Redcat 51 with an ASI 533 MC Pro and ZWO OAG with an ASI 290 guide camera. The mount sits on the TC40 tripod.
Most of the time it sits on my grass in my backyard. I use the ASI AIR polar alignment routine and have no problem getting < 30" from the pole.
I image with the ASI AIR Plus using guide intervals of 1s. Typical image exposures are 2-5 minutes.
Normal nights the guiding is ~ 0.5" rms. Some nights are exceptional and the error drops to <0.4". This is way better than needed for my imaging scale, so I don't spend much time trying to improve it.
The mount has been a whole lot of fun. It is easy to carry around, even with the scope/camera on top (no counterweights). It is the mount that will be taken on a plane to image next years eclipse!
- Tom C

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Lasse Skov

Topic starter

Oct 21, 2023

Tom Carrico:
I cannot find my report, but I recall my AM5 that I bought December 2022 had an error of about +20/-16". I use a Redcat 51 with an ASI 533 MC Pro and ZWO OAG with an ASI 290 guide camera. The mount sits on the TC40 tripod.
Most of the time it sits on my grass in my backyard. I use the ASI AIR polar alignment routine and have no problem getting < 30" from the pole.
I image with the ASI AIR Plus using guide intervals of 1s. Typical image exposures are 2-5 minutes.
Normal nights the guiding is ~ 0.5" rms. Some nights are exceptional and the error drops to <0.4". This is way better than needed for my imaging scale, so I don't spend much time trying to improve it.
The mount has been a whole lot of fun. It is easy to carry around, even with the scope/camera on top (no counterweights). It is the mount that will be taken on a plane to image next years eclipse!
- Tom C

Hi Tom

Thanks for sharing. It’s interesting that you use an OAG for a Redcat and it’s short focal length. Does it work better for you than using a guidescope?

Lasse Skov

Topic starter

Oct 21, 2023

Ashraf AbuSara:
I don't think there is a direct correlation between PE and tracking error as much as it is the steepness of the slope of your PE. The steeper the slope, the more corrections your mount has to make quickly and the harder it is to maintain a low RMS error. Also there are numerous confounding factors that can significantly affect tracking error with harmonic mounts. Setting the right aggression, correction period, guided exposure rates etc is important. Additionally Harmonic drives in general and AM5 in particular is very seeing dependent. So if you live in an area with poor seeing your guiding maybe significantly worse than an area with generally good seeing, no matter how good the version of the AM5 you got.

I have learned to ignore the test report. I think it is not very useful to draw any conclusions. I currently operate a C11 at a FL of 2065mm with a 0.7x Starziona LF reducer with the AM5 mounted on the TC40 tripod and depending on the location of the target and seeing conditions my RMS error can range from just below 0.3" to 0.6" even in mild breeze. Targets closer to the celestial equator are more difficult to track so I tend to get 0.5-0.6", but anywhere around Polaris can easily track 0.3" all night long.

Hi Ashraf
Thank you for your input. I’ve seen a lot if forum posts taking about getting “a good unit” when taking the AM5. That’s why I thought that the test report was important when taking expected guiding.

Tom Carrico

Oct 22, 2023

Hi Lasse,
I always use an OAG for guiding. For me it is just simpler and I never worry about flexure. Finding guide stars has never been a problem now that we can guide in front of any filter we might be using.
- Tom

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Robert Žibreg

Oct 23, 2023 · Edited: Oct 24, 2023

Scope
Askar FRA500, (500mm native and 350mm with reducer)

Max & Min Periodic Error
15.5 / 6.3 Arc-secs

General RMS error (using a ASIAIR PLUS)
0.3 - 0.4" OAG

But min/max periodic numbers are useless and ZWO should calculate it differently, depending on maximum slope of PE. I recommend you to go over thisthread. Depending on my maximum slope, my error is 0.23 arcsec/sec, everything else is seeing related. It also heavily depends on guide exposures so I keep mine at 0.5 sec if possible.

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