Getting the best performance from my AM5: Page 16

Getting the best performance from my AM5

Kevin_A

w7ay i did manage to get 1 good image of NGC 7000 last night with my Rokinon 135 and 183mc pro and guiding was 0.5 or less all night long. I did restart autoguiding every hour as you recommended in asiair.

w7ay

Kevin_A guiding was 0.5 or less all night long. I did restart autoguiding every hour as you recommended in asiair.

Try it again soon before the hour angle of North Amera changes appreciably from last night, but this time, don't re-start autoguiding and let it run until a Meridian flip. See if it gets worse on the long term.

Speaking of which, I suspect you do not have to even do a Meridian flip and not have anything smashing together. That is what I plan to do with the Samyang 24mm and the AZ-GTi. I think I can let it run well past the Meridian.

Nice wide field even with an ASI183!

Did I Itell you that I just finished lashing up an EAF setup with a Canon 100L/2.8 "macro" lens with the full frame ASI6200MC? That should give me lots of FOV. The Canon will be stopped down to somewhere around f/3.9 -- even a Canon-L is not capable of being fully open.

Just got a ZWO EOS adapter with a M54 hole to use. The existing EOS adapters that I have are all M42 based, which would vignette like there is no tomorrow with the full frame sensor.

What narrowband filter were you using? There are halos even on moderately bright stars. Fortunately, Deneb is just off the frame, otherwise it would be really obvious. But it is already obvious on Xi Cyg, which like Alnitak next to the Horsehead is one of the stars I use to test narrow band filters with. Xi Cyg ruins North America just like Alnitak ruins the Horsehead.

But, I think this is the first time I see halo around 60 Cyg! I think the H-beta and OIII bands of the filter must be the biggest culprit since 60 Cyg is a bluish star.

Chen

Kevin_A

w7ay i was using a tame l-enhance filter but at f2.8. The halos are from processing as i just quickly did a starnet++ in Siril. I have never been able to get it to work until yesterday as it would crash my computer and force a hard restart. I adjusted my bios and now it runs… but that image was just a quick grab n go with no delicate touches… so a bit of halos from bad processing and only 3.5 hours of 180s subs! Haha

AstroBen60

w7ay

Hi Chen

I just would like to come back to the initial Harmonic mounts topic, and ask you what you think about the bad experience I had recently, as you seem to have a wide knowledge of these mounts.

Two days ago, I was installing everything on my mount, hardware, softwares, checking that everything was working fine together. NINA, focuser, filter wheel, mount, stellarium, etc etc.. Everything was fine.
I then parked the mount and went out.

The morning after, I had an horror vision.
I saw the scope crashed in the tripod. The red light on the power button made me realize I forgot to switch off the mount. What was strange is that I didn't ask for any tracking. And as far as I remember, the T red light on the hand controller was not lit up. ( but I'm not 100% sure about this point though)
Nothing looks to be damaged regarding the imaging stuff. And no bad mark on the tripod or the filter wheel could make me thing it really drove with tremendous power the gear in the tripod Leg.

Fisrt, if it was tracking, I can't understand why, as I asked for a park.
I thought about the refractor having fallen, but there is normally a brake on RA axis.
I tried to get some informations about motor stall for these mount, and I was replied there is a stall protection only when slewing at 1440x.

So I don't know what to think about that.

Do you think it might have damage the mount?
What could have happened ?
These mount are known for a really high torque, but it doesn't look like there was something really pushing hard the scope into the tripod. Is there any mechanical device that could act as a "circuit breaker"? Or might the motor have instantaneously stalled anyway, despite the reply I had? Might any belt have skipped all night long until I discovered it

And finally, what could I do to check everything is working fine? ( "pseudo night" starts at 11.50pm here now.. For 2h.)

Thanks a lot for tour help

Ben.

AstroBen60

Kevin_A

The halos are due to the L - enhance filter.
I once tried it, it's really not a good filter for that.

Kevin_A

AstroBen60 nope, l-extreme filters give halos, not from l-enhance even on my fast f2 rig. . It is from using Starnet.
Without using starnet there was zero halos on any of my images.

w7ay

AstroBen60 you seem to have a wide knowledge of these mounts.

I have been using an RST-135 since 2019, but do not have any experience (nor plan to) with any ZWO mounts.

I saw the scope crashed in the tripod.

This is not a strain wave gear issue, but a ZWO issue. The torque from strain wave gears do make them much more dangerous when they run without proper limits.

Is there any mechanical device that could act as a "circuit breaker"?

The RainbowAstro mounts senses the current draw from the servo motors and will back off the current when it senses a sudden rise of the current draw -- indicating that some part of the payload is hitting the pier -- the ZWO mounts use stepper motors instead of servo motors (difference is one has analog motion while the latter moves in quantized motion), they may be harder to monitor, assuming ZWO had even added some circuitry to monitor the motor current.

What was strange is that I didn't ask for any tracking.

Did you send a GOTO to the mount at some point? Traditionally, (almost) every mount I know will start tracking only after completion of a GOTO, and stops tracking when it hits some limit (meridian, horizon), or when asked to go home. I do not know any (working) mount that starts tracking by itself from the home or parked positions.

(As I mentioned, I do not own a ZWO mount; both my active mounts are RST-135, so I really have no idea what all the blinking lights on ZWO mounts are about.)

Fisrt, if it was tracking, I can't understand why, as I asked for a park.

Yep, definitely a ZWO bug.

Nothing looks to be damaged regarding the imaging stuff.

Tracking is only moving the RA axis by 15 arc seconds per second of time, so I don't expect too much harm, unless it has crossed the meridian and potentially twist the instrumentation's connectors and tearing them apart. Yes, a strain wave gear mount can rip a USB cable out of its own connector -- ask me how I know :-).

And finally, what could I do to check everything is working fine?

I have no idea, Ben.

Personally, I would record everything (hope you took some photos after the accident), especially start warning your dealer of a potential problem, since it is not your fault, but the fault of the mount's manufacturer. This will prepare them in case you need to return it. FWIW, I would be more concerned about your expensive instrumentation than a cheap mount -- since there is probably some fine print that harm to your instrumentation is not covered.

"pseudo night" starts at 11.50pm here now

Hah, I know -- we didn't leave astronomical twilight here until 11:40pm last night. And we entered twilight again at 2:45am. At least the longest day is past us now. Even after leaving astronomical twilight, the average ADU of the background skies continue to drop for at least another half hour.

Chen

Kevin_A

w7ay do you see the zigzag pattern in dec and ra in my photo that covers the full period length? Would a lower guide rate help with that or do you think that this is the best it can do without getting a better guide camera! Looks like it just can’t control the overall periodic error well on top of the random spikes.

Kevin_A

Yes, getting back n track… I am starting to agree that the biggest issue with these mounts as that a lot of the issues people are having with these mounts is that the partial graph only shows the biggest part of the PE, but the worst PE slope might be in an area where the PE magnitute is smaller. I think that once zwo adds different guide rate adjustment in Asiair, it will be helpful to a lot of mounts. People still need to understand that this is not a high end mount and it was introduced as a light weight amateur portable mount only. I laugh when people say they plan on using a 11” edge or similar and think it will work as well as a Cem120ec. Good luck with that.

Kevin_A

This is my typical guiding no matter how low or high I set my max durations and no matter if I use 0.5, 1 or even 2 second exposures. It runs around 0.5 and has little blips and so fast my stars are round still. It is probably their average design spec. Once zwo lets me adjust the guide rate I think it will allow me to tame the sawtooth guiding that still exists even with low aggression and low pulses. Time will tell. It still guides better than my past 2 iOptron mounts (Gem28, 45) and my resolution of my scopes are 1.2, 1.6 and 3.6 so guiding under 0.7arcsec rms is ok for me. 0.35-0.4 would be nicer! Haha

Kevin_A

@"w7ay" do you see anything in this chart that i could try to lower the zigzag over the period length?

w7ay

Kevin_A do you see anything in this chart that i could try to lower the zigzag over the period length?

Kevin, you appear to have a mount that consistently gives large errors (up to 2"). Notice that when the error grows for RA, they often also grow for declination. But not always, and not always with the same signs.

That leads me to think it is just a mechanical imprecision thing (that is why you buy mounts from companies who treat it is an engineering project instead of an MBA project). But it could also be bad centroid computation too -- I notice that you are using a rather small guide scope with 162mm focal length, with a plate scale of 3.69 arcsecond per pixel. Try exactly the same setup (don't change anything else but the guide scope) with a 250mm to 350mm focal length scope and see if the graph changes.

Now, 3" of error may well be good enough for your main OTA (assuming you chose a small guide scope because you also have a small main OTA). So, it really depends on what you expect from a cheap mount.

Do you still have the data? If so, could you expand the x-scale so that we can see what leads to the large errors? Like, expand the region around 22:20, so we can see the actual correction pulses (turn the correction pulses on) by every second (I notice that is your guide rate).

You must have a lot of patience. By now, I would have ditched the mount and not throw more good money after bad.

Chen

w7ay

Kevin_A Would a lower guide rate help with that or do you think that this is the best it can do without getting a better guide camera!

Can't tell until we can see the correction pulses. See if you can expand the scale of the graph and see the individual correction pulses.

Problem is I don't see any region where the error is less than 0.5" (uncorrelated 0.5" RMS error in RA and declination will lead to a total RMS error of 0.707").

Chen

Kevin_A

w7ay patience is my middle name.

w7ay

Kevin_A

OK, it looks like this is NOT the case of insufficient max pulse durations. Notice that the correction pulses do not consist of a constant amplitude comb. If there is insufficent max pulse, all of the correction pulses would be maxed out, producing a constant comb (think a crew cut :-). But we see correction pulses of different amplitudes.

So, the next question is why is the guide graph (which plots the centroid of the guide stars) swinging so badly. There are two prime candidates: (1) you have hit some spot on the mount gears where all of a sudden the errors became huge (like 2" huge), or (2) the centroid computation is fubar.

I tend to favor case (2) [I am an "occam's razor" type guy] since the likelyhood that you hit bad spots of the gears on the RA motor and the declination motor at the same time is small, unless you have something loose that can couple the RA axis to the declination axis (but I assume you have tightened every dovetail plates there are; if not, check how securely the guide scope is held down, relative to the mount itself, not relative to the main OTA -- this is why I use a dual saddle plate with an independent guide scope mount).

Try a much larger guide scope with a flat field, and make sure you have no fewer than 12 stars running in multi-star guiding (don't be shy with the guide camera gain setting). And make sure that the stars which are selected all have similar brightness. Don't let a single bright star dominate the mean of the centroid, since ASIAIR uses SNR as a weighting function -- a very bright star in multi-star guiding becomes a single star guiding, and yu will need guide exposures that are long to counter "seeing." Increase the gain of the guide camera sufficiently so that the first couple of guide stars get rejected because they saturate.

If it is a case of bad centroid estimation (my suspicion), then nothing with the guide parameters will help. I.e., max pulse won't change anything, guide rate won't change anything, etc, (even changing to a 10Micron mount won't change anything) since the measured centroid is bogus, and causing those excursions in the guide graph. You are attempting to move the mount based on bad data (centroid). At the same time, you are needlessly (and erronously) issuing guide pulses that should not be issued. What you need is better centroid estimation.

As I mentioned earlier, your guide scope may well be appropriate for your main OTA. 3 arcsec may be good enough.

Chen

Kevin_A

w7ay that is why I have been asking you a lot of guide camera related questions.
On my tiny Rokinon setup, i can not use much more of a guide scope size increase but i will try bumping up the gain even further since i did notice that 1 to 2 stars of the 12 were much bigger than the rest. Is worth me trying to bin2 the guide camera to get more star definition? I have both 290mm mini and 120mm mini cameras and my only concern will be my biggest scopes as my tiny rokinon setup is a 3.6 image resolution so sub arcsec guiding wont be as important. My 162mm is a f3.2 50mm dia doublet guide scope and it is fairly decent… but my stars on all my guide scopes seem very blobby so maybe i should try a fma180pro when they become available. Do you think that a 0.25 guide rate will help also when asiair impliments it? Sorry for so many questions but it helps my patience! Haha thanks Chen!

w7ay

Kevin_A Is worth me trying to bin2 the guide camera to get more star definition?

With your guide plate scale, that would be disastrous!

You are already at 3.6"/pixel. Bining by 2 would make it over 7" per pixel! You need to go the other way (i.e., by using a longer focal length).

Do you think that a 0.25 guide rate will help also when asiair impliments it?

Not when the guiding system is given bogus centroids to start with.

it helps my patience!

Not mine.

Chen

Kevin_A

w7ay haha. I think I will just have to try a better guide scope like the 180 or 230 with flatteners. I thought that binning while worse might increase the centroid size just like a lot of people say that out of focus guide stars are better for phd2 to find the centroid. That was my point. I think I am getting to the point of trying anything unconventional as I have tried and used everything that makes sense and what should actually work. I often wonder if it is a asiair issue or bad guide scopes since all 3 of my guide scopes (240, 162, 120mm) and guide cameras seem to have low quality guide stars or I may just have 3 bad guide scopes.

w7ay

Kevin_A I often wonder if it is a asiair issue or bad guide scopes since all 3 of my guide scopes (240, 162, 120mm) and guide cameras seem to have low quality guide stars or I may just have 3 bad guide scopes.

I have had no problems with ASIAIR guiding once they upped the guding frame rates to 2 FPS, and even better recently after dropping my guide rate to 0.25x sidereal.

But you need good centroids first -- I don't use tiny guide scopes or small sensors. The smallest guide scope that I used in the past was a Borg 36ED (focal length 200mm). And since then, Borg 55FL, and in the past month or so, an Askar 180p. I also abandoned the ASI290MM class cameras, and went to an ASI178MM. A QHY678M arrived today from Agena, and I will start some time experimenting with that (writing my own software on INDIGO), replacing the ASI178MM.

FWIW, I also use Bahtinov masks to focus my guide scope (lately, with EAFs) as best as I can.

Chen

Kevin_A

w7ay i think i might buy a smaller pixel 178 as i am not fond of the 290 either as I expected better images. I think I will see if I can find a better guide scpoe too. Borg 55fl may be a bit too much for my liking but maybe a better 60mm william optics 61 doublet or SW evoguide 50DX. My cheap Chinese 60mm is garbage so maybe it is just poor star images that is the core issue as my past 2 mounts had similar guiding roughness issues and now there seems to be a commonality. Thanks.

w7ay

Kevin_A SW evoguide 50DX

I do have an Evoguide 50ED with field flattener, but the construction is amazingly rough and heavy, I didn't bother to attach an EAF to it, and thus have not tested it so far. The threads on it look like they were machined in a high scool machine shop.

If the 50DX is like the 50ED, the focuser is rather odd -- the focuser roughly turns one way to get rough focus, and from there get a small region to use as fine focus in the reverse direction. I have not tried to tap a set of holes to mount it, and I am not terribly fond of tube rings of the 50ED.

EVOguide and FMA180p side by side:

Whatever you use, make sure that the spot digram of the OTA is good all the way to the image circle of the ASI178, and preferably wider, to plan for future better cameras.

Also, if you don't already have an ASI178MM and are not stuck with the ASIAIR, you might as well go to a monochrome IMX678 sensor (with 2µm pixels), like the QHY678M camera. A larger sensor is even better.

Chen

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