A modest start of astro season: Arp 170

[wimvb]

This target was chosen by chance, because after having set up my equipment, I wanted to test it, especially guiding. I used the new guiding routines in Ekos/Kstars: multi star guiding and predictive PEC guiding.

During summer recess I took my mount apart and cleaned and regreased it. I also increased tension in the RA belt. This improved guiding, but I still have a 120 s periodic error that wasn't guided out yesterday. The timing pulley attached to the RA motor is not quite centered. I have ordered a new pulley from beltingonline, which hopefully will resolve this issue.

Anyway, here is Arp 170, or ngc 7578

The main galaxy in this image, ngc 7578, is located approximately 550 Mly from earth, and even most of the other galaxies that you can see are at about this distance. I identified only one galaxy that is more than 1 bilion ly from us, it's hardly visible as a small red dot near the upper edge.

2 hours of RGB data (no Luminance), processed in PixInsight

Equipment:

• SW MN190 on a SW AZ-EQ6 with oag
• ZWO ASI174-MM Cool camera with ZWO RGB filters

Software:

• Ekos/Kstars for acquisition
• PixInsight for processing

No flats yet, so there is vignetting left in the lower left corner.

(click on the image to get to the larger version)

Edited September 14, 2020 by wimvb

[MarkAR]

Great result, how did you find the new guiding routines?

 

[wimvb]

6 hours ago, MarkAR said:

Great result, how did you find the new guiding routines?

 

Thanks. The jury is still deliberating on this, so to speak. In PHD I always use the PPEC guide mode, so if it's just as good, and I can do the same in Ekos, that means one less piece of software to bother with. I also still need to dial in the settings, as the algorithm missed a 120 s period that was quite strong (I had preset 480 s).

The multi star algorithm had no problem finding 6 or 7 stars to guide on. And that was away from the plane of the Milky Way, with a simple asi120 camera. It also picked some areas where there were no stars, and I see the need to create a dark library for the guide camera. I also wonder if my limited fov is enough to average out seeing, which is the purpose of multi star guiding. As long as it works at least as good as single star guiding, I'll keep using it.

In short, it takes a little effort to dial in the settings for the new routines, but they are enough plug and play to use them as is. And let's face it, PHD is hardly "push here dummy" anymore either.

[andrew s]

If the 120s pec is smooth I am very surprised it was not guided out. I am not familiar with your software but I would have expected this to be taken care of with basic settings. Was the gain/aggressiveness set low?

Regards Andrew 

[wimvb]

20 minutes ago, andrew s said:

If the 120s pec is smooth I am very surprised it was not guided out. I am not familiar with your software but I would have expected this to be taken care of with basic settings. Was the gain/aggressiveness set low?

Regards Andrew 

I kept the settings at default for this session, just to get a baseline. Last season ended for me with almost erratic ra guiding, which turned out to be caused by too low belt tension. Honestly, I also expected this 120 s period to be guided out, and with ordinary guiding, it probably would. But ppec uses a combination of proactive error correction and reactive guiding. As such, I would think that the reactive part is less aggressive than usual. Next session I will concentrate on dialing in the settings. Presetting a 120 s period in ppec guiding should give better results.

SW have also done a rather sloppy job with the belt drive in my mount. The ra timing pulley is visibly eccentric. It may only be the top flange that is off centre (in which case it shouldn’t affect tracking), but just in case, I have ordered new pulleys from beltingonline.

[wimvb]

12 hours ago, andrew s said:

If the 120s pec is smooth I am very surprised it was not guided out. I am not familiar with your software but I would have expected this to be taken care of with basic settings. Was the gain/aggressiveness set low?

Regards Andrew 

I caught a gap in the clouds and am testing some more. Now I've set a fixed period of 120 s and tweaked a few parameters (such as single sided DEC guiding). After a few periods, the guiding rms is down to 0.63", half my imaging scale. I'm pleased.

[andrew s]

24 minutes ago, wimvb said:

I caught a gap in the clouds and am testing some more. Now I've set a fixed period of 120 s and tweaked a few parameters (such as single sided DEC guiding). After a few periods, the guiding rms is down to 0.63", half my imaging scale. I'm pleased.

Good news. Looking like your in the right track. Regards Andrew 

[gorann]

12 hours ago, wimvb said:

I kept the settings at default for this session, just to get a baseline. Last season ended for me with almost erratic ra guiding, which turned out to be caused by too low belt tension. Honestly, I also expected this 120 s period to be guided out, and with ordinary guiding, it probably would. But ppec uses a combination of proactive error correction and reactive guiding. As such, I would think that the reactive part is less aggressive than usual. Next session I will concentrate on dialing in the settings. Presetting a 120 s period in ppec guiding should give better results.

SW have also done a rather sloppy job with the belt drive in my mount. The ra timing pulley is visibly eccentric. It may only be the top flange that is off centre (in which case it shouldn’t affect tracking), but just in case, I have ordered new pulleys from beltingonline.

Seems that you have to be lucky with SW mounts, or you will have to spend time as a mount mechanic. Fortunately I am quite happy with my NEQ6 and EQ8 (after fixing backlash). They give me 0.8 and 0.4 guiding, respectively, on good seeing nights. So I just keep my fingers crossed that I will not have to take them apart. For my Mesu, guiding seems only to be limited by seeing or wind, but that is Mesu.

Edited September 14, 2020 by gorann

[wimvb]

Another clear night this week allowed me to do some more testing and collect luminance data for this target.

This is the original RGB image with added LRGB using 72 minutes of luminance (36 x 2 minutes)

The added luminance gave less noise and tighter stars.

(click on the image to view the full size version)

Enough testing, next clear night I'll be aiming at something more interesting.

[wimvb]

On 14/09/2020 at 02:18, MarkAR said:

Great result, how did you find the new guiding routines?

 

The jury is back with a verdict:

Now that I have the parameters dialed in, the new routines are definitely going to be part of my toolkit. I don't think I'll be using PHD2 anymore. I do like the user interface of PHD2 more, and all its gadgets, but the internal Ekos guider now works equally well and is actually easier and faster to get starting; more "push here, dummy" than PHD. And I can still use phd log viewer to analyse my guide logs

[andrew s]

Glad it all works. Regards Andrew