Getting the best performance from my AM5: Page 30

Getting the best performance from my AM5

wookash

Thank you, Chen!

So, assuming 0.6” slope and 0,5sec exposures I will need to start from 150-200ms max RA duration and work from there?

What about min move (in phd2)? Shall I set it to 0.1px or rather keep at 0.2px? My guide scope image scale is 3.16 arcsec/px

What kind of RMS should I expect?

I read most of the posts here and noticed you’ve mentioned AzGti a couple of times. It’s actually my current mount. It was interesting to see you’re comparing it to ZWO harmonic drives. I was not aware of this ratio (that gear mount 1/3 of the price of harmonic drive will perform the same). Still, I expected better guiding than with my AzGti and still hope to achieve it .. but for this I need good weather.

w7ay

wookash So, assuming 0.6” slope and 0,5sec exposures I will need to start from 150-200ms max RA duration and work from there?

Sorry. I do not answer questions on settings for ZWO mounts.

Chen

wookash

w7ay no problem. Thanks

Kevin_A

wookash use 0.1px as it will be better than 0.2px minmo using 0.5s guide exposures. You have to remember that these mounts are not meant to be great precision mounts, but meant to be very portable good mounts.
Use the mount and test it and if you do not get under 0.7rms consistently as zwo advertises then return it or contact them to get it fixed so it does meet spec.

wookash

Kevin_A thanks. I don't have good weather recently but it looks like I should be able to get between 0.5-0.7 RMS, still need to test it for a longer period and with better visibility

wookash

a couple of more questions:

are you guys using DEC backlash compensation in PHD2? I've switched it off
I've set Hysteresis to 0 - has anyone done the same?
Which algorithm are you using for DEC guiding (hysteresis or resist switch)?

Kevin_A

wookash i donot use dec backlash compensation and use resist switch for dec.

mconsidine

Ceat Hi, Can you tell me if the :Rv command would also work in this case, ie to enable the equivalent of the ASCOM MoveAxis command to be created in an app that doesn't use ASCOM? I'm on a Linux box and would like to code a routine for tracking artificial satellites. Thank you!

Jan75

Can I pick your brains on a question that has been tormenting me for a while? I read most of the posts here, learned a lot and applied that knowledge to fine tune my AM5 guiding. The RMS that is displayed in the ASIAIR app is now routinely in the 0.3"-0.5" values which should be as good as this mount can possibly do. Right?

BUT! While this RMS value is consistent over several hours, the resulting stars on EVERY frame are elongated in the RA direction (i.e. with identical dec value). See a 100 % crop below from last night, as an example (integrated image here but individual light frames look the same). The Dec line is the one ending in the top left corner. Pixel scale is about 0.50"/px. All stars in the field have the same form so this is not an optical train problem (it also goes away if the exposure is short).

What could be causing this?

For illustration, here's a screenshot of the guiding screen in the app - again from last night, so this correlates with the elongated blobs above:

The guiding numbers are false positives (too good to be true). Issue happens with RA only so this is clearly a guiding problem. Could a sloppy focus of the guide scope cause this, maybe? Anyone seen this before?

MrAstro

Jan75
I am thinking loudly here..
This means the issue is occurred in the main imaging setup BUT not in the guiding setup and that might be:
Flexure, Cable hanged or dragging, Something loose in the main imaging setup .
By the way, Did you share this issue in Cloudy Nights forum? If yes, Please share the link here or at least the title of your post, I want to see what other users say about your issue for the sake of knowledge.
Hope you the best !!

w7ay

MrAstro Something loose in the main imaging setup .

The first thing I would check is what focal length was given to ASIAIR in the Guide Settings. Remember that ASIAIR uses that focal length to estimate the guiding plate scale (since it knows the guide camera, and thus pixel size of the guide camera), and report the guiding error in angular distance (arc seconds).

With the main OTA plate scale at 0.5" per pixel, the elongation could also have come from the ZWO camera fans (known for bad vibration) instead of some other systemic mechanical problem. A long exposure with the cooling/fan turned off would be a reasonable test. If the elongation does not become wore with an increase of exposure time, the problem is more likely to come from vibration instead of flexure.

A before/after Meridian flip test would also help pinpoint where the error is coming from.

Best to adjust the guide camera angle and the main OTA camera angle to be aligned with RA or declination axes. That will make it much easier to pinpoint the source of the error.

Chen

MrAstro

w7ay
Very informative reply..

w7ay Best to adjust the guide camera angle and the main OTA camera angle to be aligned with RA or declination axes. That will make it much easier to pinpoint the source of the error.

Could you give details how to do that.. If we can see any hand skitch drawing it will be nice.

Thanks!

w7ay

MrAstro Could you give details how to do that.. If we can see any hand skitch drawing it will be nice.

Remove the camera and look at the sensor. Note the long and short axes of the sensor relative to the camera body. It is usually oriented to align with the USB connector or fan screws. I usually mark all of my cameras using some Gaffer tape, and always align my main OTA so that it is either aligned North-South or East-West.

To align the camera so that the long axis is oriented North-South, use the camera angle adjuster and rotate the camera body so that the long axis of the sensor is parallel with the declination plate. I.e., as you slew the declination motor, the long axis mark that you made to the camera remains parallel to the declination plate that holds the OTA. Rotate the camera by 90º if you want the camera angle to be aligned with the RA axis.

You can confirm this (and get more accurate angles) by looking at the plate solved results, but you might be pleasantly suprised at how close you can get by just "eyeballing" it. I usually get within 1.5º by just eyeballing -- the human eye-brain is very sensitive to detecting vertical structures.

PHD2 applies the correct coordinate rotation (part of what is discoved duing "guide calibration") to match the camera image (in camera pixels) to the mount (in declination and RA) -- that is why you don't strictly need to align your guide camera angle. But when things don't come out as you expected, it is best to also align the guide camera angles too -- it can't hurt when debugging problems.

You will find observatory images are often N-S or E-W aligned. Quite often, with plates that show North at 12 o'clock.

Chen

Jan75

MrAstro No I didn't post this anywhere else for now.
w7ay Thanks for the ideas, I'm not ignoring your advice, just wasn't able to get to my scope due to vacation and bad weather. I'll align the cameras' (main, guide) field along the RA and Dec grid. I'll also test the same exposure with the fan disabled and I'll report back! The star shape does not seem to get worse with longer exposure times but again let me run a few tests and get back here. Sorry again for the long time to respond.

mikewagnercmp

Here is my mount. I picked the highlights slope, which if i did the math right, gave me a max of about .20 arc seconds / sec. I also fed the picture into chat GPT and amged to get .31 as its answer. I'm not sure I trust GPT, but I'm sure I could have picked a less steep slope.

I got the mount secondhand but never used. it came with clouds, but I was able to get it out and get test it, based on some of the info in this thread (I am about 60% of the way through reading this whole thread) I was able to get my guiding to RA of .62 RMS and dec of .37 RMS.

I am using a Orion ST-80 short tube achro refractor as my guide scope, with a Touptek imx290 based camera for guiding. It was always fine for my traditional mounts, but I am not getting 12 guide stars. I have a dinky Svbony 50mm guide scope I could use as well for a wider field, but not sure that would really help.

It is supposed to be clear tonight, so I plan ti image a bit more and mess with guiding. I should mention, that I use a 6' newtonian as my main scope. This mount already seems to guid better than my ancient g11 so I am happy so far.

Anyone have an opinion on my graph from ZWO, or using the smaller guide scope ?
Thanks in advance,
Mike

Jan75

mikewagnercmp Mine is way worse at 0.38"/s based on the report, meaning it could actually be worse since the report captures the area with the highest PE, not with the fastest PE change rate. But this does not seem to be a problem as even 0.38"/s does not happen every second and fast autoguiding should fix it most of the times. Other factors will kick in before the mount PE error rate does, such as seeing, optical train issue or the mysterious shaking that has been plaguing my setup (see my previous post).
With your Orion ST-80 you likely won't run into most of those issues since the combination of the scope and your camera has a resolution of about 1.5" per pixel (or more if you use a reducer) so any movement below that value won't likely even be visible in your picture.

mikewagnercmp

Jan75 My guiding is actually pretty good, so I am happy. there is an occasionaly RA excurion, but generally per PHD its around .3-.5 rms. Dec is much less.

In the log analyzer the RMS numbers are higher generally but still under .5 for both axis. I can image with a scale of .88 on my main scope and have no issues thus far.

Jimfmiller

StarzLite Thank you for the article. I am using PHD2 vs ASI Air. Why are there 2 screen shots for each of your guiding examples, with the
lower screenshot seemingly having better results?

Many thanks

Jim

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