Getting the best performance from my AM5: Page 8

Getting the best performance from my AM5

w7ay

RogerioS I have a 50mm

No, you had earlier mentioned that you have a 30mm guide scope

REDCAT 51
ASI294MC PRO
Guider ZWO30F4 (ASI120mm)

You need a guide scope and a guide camera with a large FOV, so you can get at least 12 pin-point (no wings and other aberrations) guide stars consistently. That part has nothing to do with your main OTA.

Chen

RogerioS

w7ay
I have two guides a ZWO30mm and a 50mm that are not in use at the moment. I believe the 50mm will be more efficient

RogerioS

w7ay Which ASI camera is best for the guide scope?

Kevin_A

RogerioS zwo asi120mm mini is budget, asi290mm mini is better but cost more. Those should be fine and not sure you would want to spend even more on a 178. Use the 50mm guide scope at least.

Kevin_A

w7ay i sold my coke bottle scope as it was horrible… same as the WO 30mm uniguide. Even the generic 60mm scopes being sold these days aee not good even with the bigger aperture….very fuzzy.

RogerioS

Kevin_A I have a generic 50mm, may be will be better than 30mm ZWO

RogerioS

Kevin_A I think I'll invest in a 174mm

Kevin_A

RogerioS i have two 120mm mini and a 290mm mini. The 174mm may be overkill for your setup as i use mine with 50mm and 60mm guide scopes on 135mm, 300mm and 644mm scopes.

w7ay

RogerioS I think I'll invest in a 174mm

Check the plate scale. I think you will find the ASI174 to be terrible unless it is on an OAG on a large SCT.

Please get a book on astronomy and astrophotography before you spend any more money.

Chen

RogerioS

Kevin_A Thank you Kevin, So I'm going to follow your advice and opt for the 290mm which is much cheaper.

Kevin_A

RogerioS it is a real good camers and smaller pixels. The 174 has big pixels that may be better suited for oag’s or bigger FL scopes. Zwo says the 290 is 30% better guiding over the 120mm mini… but thats just zwo talking. This hobby has a steep learning curve and a good place to start is Cloudy Nights.

w7ay

Kevin_A Zwo says the 290 is 30% better guiding over the 120mm mini…

ASI290MM Mini has been replaced by the ASI220MM Mini, Kevin.

Substantially larger FOV which is a good thing for multi-star centroids, lower Read Noise, and higher QE. Unfortunately, it is sensitive in the near-IR region, so if the guide scope is not close to an APO, you may need a IR-cut filter to go with it to reduce star bloat.

Also need a longish focal length guide scope, but not as bad as the ASI174, though. Other weak point is the shallow well -- so need to pick camera gain carefully for multi-star centroiding.

I got one, but not impressed. So, I am back to the ASI178MM for guiding.

Chen

RogerioS

Kevin_A Thanks Kevin.

Kevin_A

w7ay i bought a few 1.25” svbony uvir cur filters that i use on my 120 and 290mm guide cameras. They just screw on and maybe they improve the contrast a bit and reduce bloat… not sure but cheap enough not to worry. One thing i do notice is that the 290mm always seems to have a bit less contrast compared to the 120mm. It has always bothered me and figure it is due to the pixel size and well depth. I thought about binning it but that just fools the system and gives better fake numbers I think. I am not going to over think things being that this mount is really just a very portable marinally adequate guiding machine… so, I just use it and not expecting miracles. I think that some AM5 mounts run well and some not so well and that some people expect too much sub 0.3 guiding all the time even in turbulent skies. Zwo has opened a can of worms where novice newbie astrophotographers expect greatness right away without understanding all or any of the many variables that can affect guiding. It is ellevated more since each mount is unique to itself and you dont know if it is a good or bad one. At least with worm mounts you can set it mostly to other users numbers and tell if its bad right away… as i found out coming from using iOptron mounts for years.
I still remember that up until just a few years ago, i was estatic just getting less than 0.8rms from my very heavy expensve mount… i was thrilled. Now, people are not satisfied getting 0.7rms from a cheaper fly weight mount. I am happy with 0.7… thrilled actually! Haha

chaitanyakhoje

w7ay Thank you for the detailed response on this.
I calculated the slope of the first wave's right slope, I don't remember what it is called, basically its the right-side slope/declination slope of the 1st waveform, and you chose the inclination which indeed is the worst slope it seems.

So I tried changing the settings just to give it a try as you mentioned today, I set both RA and Dec durations to 133ms and started calibration pulse with 1000, then 1500, and 1800, guide scope exposure to 2 seconds.
It seems the DSO target I am aiming at, is at horizon when I start imaging (10pm PT onwards) - SH2-132 (Lion's Nebula). I use a asi120mm mini for guiding, and I noticed as time passed and the target moved upwards (around 12am PT), the guiding improved quite a bit, with the default settings on ASIAir+ (1800/2000) calibration step, max dec and RA at 2000. I know it is not what you recommend or believe to be accurate, but that still gave me a consistent total error of 0.5-0.6.

One thing I noticed which is kind of a serious problem to me is I am imaging at 300s and I notice a huge spike periodically in the total error, not necessarily RA/DEC individually, the error jumps to 3-4 etc. and it is not the dithering, because I have enabled stability parameters as well in ASIAir+.

So I am wondering what is causing this, is it because I have a high harmonic error/higher worst slope etc.
Or is this just a case of bad visibility. I live in a Bortle 8-9 but I use narrowband filters for imaging. I do my polar alignment on an empty filter slot, then refocus on a filter and start guiding. I don't necessarily need to do this, but I didn't want the polar alignment to mess up due to my sky conditions.

I guess I just want to make sure that the unusual guiding graph spikes are just because of poor visibility and not the mount itself. Any thoughts on this?

EDIT:
I want to note that, in clear conditions (lower bortle zones) 133ms max RA and DEC, calibration step at 1000/1800, 1/0.5 exposures would yield excellent results, as I saw the guiding improving on these settings way quicker than they would at other settings, but they probably would cause problems if I have poor seeing conditions quicker as well.

w7ay

chaitanyakhoje It seems the DSO target I am aiming at, is at horizon when I start imaging (10pm PT onwards) - SH2-132 (Lion's Nebula).

Does your mount support King Rate (named after astronomer A.S. King), which is an atmospheric refracted sidereal rate? You can find that in the hand controller of the mounts. If not, there is an additional tracking error that you need to deal with.

Just do a difference between King Rate and simple Sidereal Rate near the horizon, and that is the additional tracking slope that you need.

Chen

Agepi7o

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Thank you Chen again for your help and your interest in trying to make us understand.
I’m sorry I’m asking the same questions as everyone, you should be probably tired of repeating yourself.
I’ve used this post's info to recreate (My math isn’t very strong, I only know how to “remove and replace body inner parts without killing people “😜) the analysis and settings in my mount.
My horizontal extent is 1,78 units, so, using the abscissa scale, the horizontal extent of this line is 1.78*430/9,02 = 84,88 seconds
The height of that sloped red line is about 6+10 arc seconds. Call it 16 arcseconds.
So, my slope is therefore 16/84,88 = 0.18 arcsec/sec. (Is this right?)
But, if I understood correctly, I think I see a second ¿harmonic? in the graph and I don’t know how to factor it in the numbers.

Now is where I’m lost. With the initial configuration of the ASIAR (2000ms…) guiding wasn’t ok, almost 2 arc seconds RMS. After almost understanding all of this I’ve set the max dec and max ra to 250 an 400 and now the RMS moves mostly between 0,4 (very few times) and 0,9 rms; mostly 0,7-0,9 and sometimes some excursions over 1. If my calculations are OK, should I choose a different setting for my guiding? If there is a second harmonic what the numbers should be?

Do I need, perhaps, to choose 0,25x sidereal and double the limits ? (It may not be posible in ASIAR mini)

Just to complete my info: I use a ASI 120mm (120 mm FL), and the focal length of the scope is 430mm. Simultaneously I use a second Rigg with a EQ&-R-Pro and a Cesletron Edge 8 (with ASI 174mm and OAG) , and the RMS moved both days from 0,4 to 0,75 (I Have added this information in terms of comparison)

This was a long text and several questions but it would be great if I can (if possible) tune up better my mount.

Thanks again. Best regards

w7ay

Agepi7o After almost understanding all of this I’ve set the max dec and max ra to 250 an 400 and now the RMS moves mostly between 0,4 (very few times) and 0,9 rms; mostly 0,7-0,9 and sometimes some excursions over 1.

Your 0.18"/sec looks reasonable, and you have a one of the better ZWO mounts. We have seen from around 0.15"/sec to 0.3"/sec (yes, factor of two variance; pity some of the customers).

But your 250 ms pulse is completely unreasonable. Even if you give an allowance of a factor of two (because ZWO did npt give you a chart for the worst case slope location), and use 0.36"/sec, you dont need a pulse anywhere close.

If you are using 0.5 second guide exposure and 2 FPS guide speed, the mount's error would have move it by at most .36"/sec * 0.5 second between pulses. That is just 0.18" worth of error.

If you are using 0.5x sidereal rate (7.5"/sec) you will only need a pulse that is 24 milliseconds long. So a factor of 10 from what you are using. For the sake of dither recovery, you may want to increase it to around 100 ms, without hurting guiding appreciably.

You can further improve things by using 0.25x sidereal guide rate and double the max pulse with to 48 milliseconds, or perhaps to 200 ms if you want to recover faster from dither.

Chen

P.S., if you want to get my attention in the future, please be sure to add @w7ay to your post. It is by accident that I saw your post today.

w7ay

Kevin_A They just screw on and maybe they improve the contrast a bit and reduce bloat…

I use a Lumicon L1 (I think that is what it is called) to cut both the UV and the IR end in my guide scope. If not taken care of, the UV end will introduce a blue bloat (which visual observers really hate since it shows up as a blue fringe around bright objects). For non APO scopes, the L2 and L3 (again, I think that is what they are called -- pardon my memory) will cut even more from the UV end -- which is a good thing since atmospheric turbulence is worse on the blue side of the spectrum anyway. I have also tried the Baader "Semi APO" filters, which also cuts a lot of the blue end.

I use a standard pancake ASI178MM, and with a simple 1.25"tp T2 adapter, the small filter fir inside the camera flange.

Over a year ago, I had tried near-IR guiding. It did improve guiding by a little like 10-20%, but other methods since then allowed me to guide better, so I ditched the IR-cut filters to gain more guide stars; because centroid accuracy is now my tall tent pole.

Zwo has opened a can of worms where novice newbie astrophotographers expect greatness right away without understanding all or any of the many variables that can affect guiding.

Not just their mounts, the ASIAIR is another example. They forget Einstein's favorite quote, I paraphrase as "Things should be made as simple as possible, but no simpler." Or, Euclid's saying to Ptolemy "There is no royal road to geometry."

i was thrilled. Now, people are not satisfied getting 0.7rms from a cheaper fly weight mount.

Yeah, I was thrilled with 0.7" to 1" type guiding too with the EM-11 (not exactly a cheap mount either). But that was in the days where good polar alignment was hard (use a polar scope to get 5 arc minute accuracy, or waste an hour to drift align each evening, bitten by mosquitos). And we did not have multi-star centroids -- first time I read of multi star centroids was this paper:

https://arxiv.org/abs/1304.2405

Chen

Kevin_A

w7ay do you think that an OAG will be better than a 50mm f3.2 guide scope running on my fastish 300mm f5.0 Askar scope. I have a asi120m mini currently on it but am wondering whether my zwo OAG might be better. My guidng has been all over the place recently and I could also use my 290mm mini but was wondering if my OAG might improve things a bit compared to my Orion 50mm guide scope. My sky has been a bit turbulent as well it seems. Guides well then jumps around a bit even at 200ms pulses and 35 aggression settings. Looking for a better way to tame things.

Superkova

My first post here and I appreciate all the advice I have received. Thank you all and especially w7ay. I don’t know what happened here but with a little trial and error (I’m not good with math) this is what my guiding looked like with one of my AM5s the other night. This went on for 1.5hrs before marine layer rolled in average RMS ended up being 0.12 for the whole session. ES127, ASI2400, AsiAir Pro, 50mm WO guide scope with ASI290mm (28lbs load no counterweight). I just hope this is can be duplicated.

Carbon fiber mount with 30lbs of weight in the bag.

w7ay

Superkova I don’t know what happened here

You might want to do a sanity check on the focal length that you have entered in the Guide Scope Settings of ASIAIR, and make sure you did not enter the aperture of your guide scope by mistake.

Even better, temporarily open the guide camera as the Preview camera, and do a Plate Solve. After a sucessful plate solve, you will know the true focal length of your guide train.

Chen

Agepi7o

w7ay @w7ay
Thank you very much for your answer. I knew I was lost beyond the point of calculating the slope. Fortunately, it seems tonight we are going to have clear skies (fingers crossed) and there's almost a new moon. I'm going to try those settings you provided.

I was wondering whether to interchange the mounts and use de AM5 with the Celestron EDGE 8 and OAG with the ASI 174mm mini, but my experience with de OAG is that I get very few stars, with 400 gain and 3-4 secs exposures.......do you think it would be wise using that Rigg with de AM5 (instead of with de EQ&-r-pro)?

EDITED: I just saw you opinion on OAG, so I know your answer that it wouldn't be a great idea. Thanks

Thanks again for the knoledge and help you provide.

Best regards

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