Very large backlash in new AM5: Page 6

Very large backlash in new AM5

tbhausen

w7ay I can imagine, because I chased exposure failure errors with a 585MC until I canned that cable 😉

mikenoname

tbhausen If you're using the ZWO-supplied flat cable, try another good, shielded cable. I've had trouble with a couple of those. I don't even bother to unpack them now.

What cables do you recommend? I should like to find a better cable for mine.

tbhausen

I’ve had good products and service from usbfirewire.com

johncdavis200

I don't know if anyone is monitoring this thread anymore or not - but I was hoping to have someone check my math and see if my slope calculations for my zoomed PE curve are correct. I'm curious because most of my slopes are much smaller than those I was seeing reported by others. Mine are in the 0.07 - 0.09 Arc-sec/sec range, only had one that was 0.10 Arc-sec/sec. Most of those I see in this thread are in the range of 0.15 Arc-sec/sec range, so I was skeptical of my calculations - although I'm pretty sure I did them right (I'm decently trained in math and understand slope-derivative well).

So if I understand the discussion here - having a LOWER "worse-case" slope is better, meaning the corrections needed should be less in order to get good guiding (is that correct?). I'm pretty pleased that my zoomed Max PE curve is pretty sinusoidal looking - not too many odd jinks or harmonics showing up. I'm somewhat optimistic that with Chen's suggestions, I might be able to guide with this pretty well.

I'm waiting for the Pier extension to arrive - and for some clear weather - to be able to do first-light on the AM5. I'm going to use it with a variety of lenses/scopes from a 200mm camera lens up to an Teleskop-Service ONTC 8" f/4 scope.

My slopes:
(I used the WebPlotDigitizer https://automeris.io/WebPlotDigitizer/ to determine the raw points on the graph)

Slope Calculations:

Calibration of the axies:

Kevin_A

johncdavis200 just looking at your graph shape you should have no issues guiding well, as the actual shape of the graph looks very good. You can tell it is a new shorter 288 period as one cycle is 1.2 degrees not 1.8 degrees. However, this graph is just a partial graph so do not put too much value on it as it is the worst PE area but not necessarily the worst slope or shape area.

tbhausen

johncdavis200 I still think you might have won the AM5 lottery... we'll see! Mine has similar min/max PE, with a less-sinusoidal shape, but it guides well with an ASI2600MC Duo camera (always under .5" RMS, sometimes under .4" and even under .3 at times", and I haven't yet worked at optimization of guiding parameters).

tbhausen

You have a short-period mount, so it should be 287.2 rather than 430.8 sec/period.

johncdavis200

tbhausen I was just starting to wonder about that from other posts... for my understanding - how do you know that? Just because it is newer or is there a way to tell from what you see here?
Thanks!
JD

johncdavis200

@Kevin_A , @tbhausen - thanks for the infor and encouragement... I was thinking that I should be glad that my curve looks pretty regular and symetrical - without all the "humps" indicating bad harmonics. If I can just get Astronomics to ship me the PE200 pier extension, I could put it on my tripod and see what happens (well - there's the clouds too).

I'm somewhat spoiled as I have a used Mach-1 that does an excellent job most of the time, but that sucker is much heavier and bulkier than this AM5. As I'm getting older, I'm not going to be able to lug the Mach-1 out to image. So I'm really hoping that the AM5 will be adequate for my imaging. Right now my longest focal length is 800mm. I do have an RC8 that I image at 1100ish mm - that one might have to be relegated to the Mach-1 all the time.

At any rate - so appreciative of the information in this and other AM5 threads here. Hope I can contribute as I gain experience.
JD

Kevin_A

johncdavis200 the AM5 kinda likes heavier setups. Mine is the 432s period mount and runs 0.6rms with my lightweight Rokinon 135mm setup but runs all night long at 0.4rms and under with my 805mm triplet. Mine has third harmonics and a non sinusoidal curve so it blips every 30 minutes or so but you cannot beat the light weight of the mount.!

ASIMount@ZWO

Kevin_A Did you use the same guiding telescope when you used 135mm and 805mm telescope？

Kevin_A

ASIMount@ZWO yes, i used a 50mm with a 290mm mini at gain 180.
I have a 135mm setup, 300mm setup and a 644mm setup and they all guide better the heavier they are. My 135 guides at 0.7-0.9rms, my 300 guides at 0.6-0.7 and my 644mm heaviest setup guides at 0.45-0.6rms all the time. I still have small 1-2rms spikes randomly every 10-15 minutes but that is ok. When I used the asiair test beta with the increased Minmo of 0.2 compared to 0.1 my guiding got much worse by at least an additional 0.3rms over the evenings repeatedly. All imaging was done in the same sky areas when testing and on calm nights. I had no issues with either side of the meridian nor near polaris either.

Kevin_A

ASIMount@ZWO my light setup is very tight, clean and rigid too… but is far worse than my 22lb bigger scope. I think the bigger scope just dampens out the gears, wheras this lightweight setup does not. The worse guiding is not an issue due to the pixel scale but rather just an observation.

astroricco

Hello Chen @w7ay ,

would you be so kind and help me to analyze how my graph of the PE has to be interpreted if it is a good sample or not? How to calculate the crucial things like first derivative on this chart and how to interpret the result and the curve characteristics?

I would be very grateful if you could help me. Maybe guide me in some directions on important phd2 guide settings related to this curve, like as you have done it with other user's am5 chart. I recently bought the mount and I am going to do a guiding test on the weekend, but a mathematical interpretation would be very interesting!

I already sampled some data points (A1, A2...... L1, L2, take a look at the picture) with a PlotDigitizer, so you can take these values for the next calculation steps. The data points are sampled at positions where I tought a steep slope exists.

Data-Points:

Structure: Point (x, y)

A1 (308.2496608, 1.745958849)
A2 (308.4510926, -2.99307059)

B1 (309.1835719, 1.339491822)
B2 (309.0696308, -0.78521895)

C1 (309.2690278, 1.616628047)
C2 (309.3870385, -0.129330168)

D1 (309.4480784, 0.073903346)
D2 (309.6535795, -4.831408673)

E1 (310.1561419, 1.773672471)
E2 (309.7736248, -4.646650627)

F1 (310.4633761, 4.692840561)
F2 (310.3046723, 1.468822624)

G1 (310.7258479, 1.20092371)
G2 (310.8418238, -2.161661917)

H1 (311.173474, -0.794457106)
H2 (311.1042955, -2.540415321)

I1 (311.9201962, 0.212471458)
I2 (312.0015826, -2.207851851)

J1 (312.4899022, 0.286374169)
J2 (312.4288622, -1.016166086)

K1 (312.8174833, 2.6697457)
K2 (312.7401659, 0.785219373)

L1 (313.1084401, 0.018476101)
L2 (313.1898269, -2.115472828)

Note: Everybody else reading this is welcome to analyze the graph too! I would be very greatful.

Best Regards,
Ricco, Location: Vienna

astroricco

@w7ay , I'll make a first calculation attempt with the data point E1 and E2 as well as for K1 and K2.

Given data-points:
E1 (x: 310.1561419, y: 1.773672471)
E2 (x: 309.7736248, y: -4.646650627)

Calculations for E1, E2:

deltaX = E1x - E2x = 310.1561419 - 309.7736248 = 0.3825171 Degree
deltaY = E1y - E2y = 1.773672471 - (-4.646650627) = 6.420323098 arc.sec

So this would mean that witihin 0.38 Degree a drift of 6.42 arc.sec occurs, right?

Since 360 Degree takes 24 hours, 0.38 Degree will take 91.804104s because of (24*3600)/360 * 0.3825171 Degree.

From that value we can calculate the max drift rate: 6.420323098 arc.sec / 91.804104s = 0.0699350336 arc.sec/s

So with a guiding of one second the error should be no more than 0.0699350336 arc.sec.

Calculations for K1, K2:

Given data-points:
K1 (x: 312.8174833, y: 2.6697457)
K2 (x: 312.7401659, y: 0.785219373)

deltaX = K1x - K2x = 0.077317382 Degree
deltaY = K1y - K2y = 1.884526326 arc.sec

So this would mean that witihin 0.077317382 Degree a drift of 1.884526326 arc.sec occurs, right?

Since 360 Degree takes 24 hours, 0.077317382 Degree will take 18.55617168s because of (24*3600)/360 * 0.3825171 Degree.

From that value we can calculate the max drift rate: 1.884526326 arc.sec / 18.55617168s = 0.10155792684 arc.sec/s

So with a guiding of one second the error should now be no more than 0.10155792684 arc.sec.

Can someone confirm my calculation way for E1, E2 as well as for K1,K2? Is it correct?

ShinyredAM5

Honestly, wouldn't worry about the calcs. too much. When the AM5 first came out lots of us went through the process but really the calculations don't help as the graph that comes with the mount doesn't show the highest PE slope.

Best bet - stick your max moves to 300ms and your RA agg @ 55 and Dec agg @ 40 then play it from there.

Back off the aggression if you can but chances are that your mount will guide well using the above.

astroricco

@Kevin_A maybe you have an opinion on the graph? 🙂

Kevin_A

astroricco the graph looks fine and it should guide well, and just guide at 1s guide exposures and around 250-350ms max duations at 35-45 aggressions. See how that works out.

fujiokae

I have been reading this thread with a great interest but having a hard time to fully understand. I'm trying to improve the guide accuracy. Overall, it's not so bad at around 1.0 RMS but as the others reported, sometimes it goes over 1.8 and sometimes it's as good as 0.6. On the last two nights, I tried to change the settings (Calibration step, Max RA/DEC duration, Aggressiveness for RA and DEC, turning on/off "Guide Camera Bin2" and using or not using dark library for guide camera, guide exposure 1 second and 0.5 second, guide camera gain from 48 to 100) within ASIAir Plus but I didn't see any improvement. It's more like random in terms of RMS. The only tendency I experienced so far is that RMS would be better when the scope looks to the north sky (away from the equator), which sounds reasonable.

Looking at my chart, the Max & Min Periodic Error looks good. Very small. But the zoom-in chart shows more zigzag curves than others' charts. So, I'm wondering the randomness is due to this zigzag curve and it would be hard to get a stable, accurate guiding at around 0.5-0.8 RMS?

I currently use a Nikon 180mm camera lens with ASI533MC Pro on AM5 with ASIAir Plus. Guide scope & camera is ZWO ASI120MM Mini & ZWO 30F4 Miniscope. I do polar alignment as good as 0.5 arcseconds. So, RMS 1.0 is fine with the current setting but I will get a much longer refractor (around 800mm) in the future. That's why I want to achieve a better and stable RMS. And I live in the central part of North Carolina under Bortle 4 if that matters.

What numbers should I use for the guide settings? Should I use the "Bin2" feature and dark library? Or should I return it and get a replacement as my copy is not well built and impossible to achieve, say, 0.5 RMS? I bought it in June 2023. Any other suggestions / recommendations are highly appreciated!!

Kevin_A

fujiokae thruthfully the chances are you will not get a better mount when purchasing a newer one. It is a lottery. I would try using a calibration step size of 2000ms, max durations of 450ms with 0.5s guide exposures and 45% aggressions. If you are not seeing enough stars in your guide camera then increase gain from 48 to 68 or increase guide exposure to 1s. Make sure you are doing your initial guide calibration in the south near the meridian at the side you are imaging at and hit the reuse calibration tab under guiding so when you select a new or a few different targets, it uses that initial calibration again on that side of the meridian. If that does not work then buy a better mount and a bigger aperture guide scope as well.

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