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.

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ASI290MM Mini has been replaced by the ASI220MM Mini, Kevin.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

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 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

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