Image capture (in)efficiency. ASIair or mount?

[Icesheet]

I’ve recently noticed that my imaging efficiency is low. Basically, I need up to 1.4 hours for each hour of actual gathered data, depending on exposure length. I think I’ve narrowed it down to dithering and in particular the time to settle. What I’m not sure is if this is down to the settings I have chosen or the ASI air and/or mount itself. 
 

Here’s a screenshot of my current settings in the ASI air 

 

 

On my latter part of my last run I changed to dithering every 2nd frame and that helped a little. Still, it seems it’s the settling that’s causing most of the issue. After a dither the guiding is quite erratic and frequently a new exposure starts after a 60s timeout. 

For info the mount is a Rainbow Astro 135. Guiding maybe hasn’t been as good as I would necessarily want but it’s under 1”RMS in general and given I’m imaging at 2”/px I’ve not spent anytime trying to optimise. 
 

Anyone had a similar experience and can suggest a good way to approach this so I don’t waste even more imaging time?

[Elp]

What are your sub lengths? Initially I'd suggest dither less frequently depending if your dither to sub frequency is something like after every 5 to 10 minutes imaging time, also 5 pixels I'd say is too small a number for dithering (in relation to the quality of your final image, I used to use a small number but now always use 30).

I'm surprised your mount takes so long, I was going to say a HD mount settles very quickly, my hem15 is typically reimaging within 10-15s after dithering compared to the 30 odd seconds of my gem.

If your guiding is erratic after a dither are there any sources of vibration, wind, what's the tripod like?

Not sure but maybe try increasing the settling time, it might be at 5s your setup may not be dampening down.

Edited November 21, 2023 by Elp

[Icesheet]

 

3 hours ago, Elp said:

What are your sub lengths? Initially I'd suggest dither less frequently depending if your dither to sub frequency is something like after every 5 to 10 minutes imaging time, also 5 pixels I'd say is too small a number for dithering (in relation to the quality of your final image, I used to use a small number but now always use 30).

I'm surprised your mount takes so long, I was going to say a HD mount settles very quickly, my hem15 is typically reimaging within 10-15s after dithering compared to the 30 odd seconds of my gem.

If your guiding is erratic after a dither are there any sources of vibration, wind, what's the tripod like?

Not sure but maybe try increasing the settling time, it might be at 5s your setup may not be dampening down.

For RGB it’s 120-180s and for narrowband it’s 300s. I did change to every two and I suppose I could go to every three frames for RGB exposures. Ok, interesting to know that 5 pixels was not enough. So, going to 30 you noticed a difference in the final image?

I haven’t spent much time analysing the mount to be honest but I am aware that sometimes it doesn’t play well with a 12v power supply and that’s what I’ve been using, so I may have to look into that as a potential source. I use the Sightron carbon fibre tripod and I don’t think wind is a factor here. It’s pretty stable when just guiding normally. Just seems to go haywire after a dither. Would dithering induce vibrations?

[Elp]

Dithering might introduce vibration but the movement is so small I wouldn't have thought it significant. Dithering by more distance I did see a better result, it was suggested by other members.

Something I haven't suggested, which might be the culprit which I've mentioned a number of times in other threads, late last year, early this year I updated to the 2.0 asiair app version and it contains the appropriate firmware updates to the airs. My once workmanlike asiair pro suddenly became as useful to AP as a brick, I also had issues with my mini. I wasted so many sessions trying to find out the issue as it would usually be something different every time causing an end to the session but the often ones were it'd fail plate solving after the second iteration try then slew the telescope in a kamikaze dive towards the ground and the tripod, sometimes stopping responding to commands full stop, turning sidereal tracking off by itself mid plan, and the one similar to yours, after dithering it'd kamikaze again and the next two to three subs would be star trailed before it decided to recentre and star again, then do it again after the next dither and so on. It was related to the sidereal turning itself off as far as I know so obviously you'd lose your guidestars.

Solution? Well I was lucky enough to have an old beta asiair app version on an old phone, this is important because when you roll back the airs firmware, connecting back to them with the old app doesn't force update a firmware installation because it doesn't have one. So I'm using the factory firmwares on all my airs. Haven't had a single problem since.

 

[ONIKKINEN]

You can safely drop the dithering rate to something like once every 20 minutes if you have one of the newer cooled Sony sensor cameras (not sure about others). You will want to calibrate with a bad pixel map in that case, as hot pixels could otherwise remain in the stacked image. Think i recall reading that some imx571 users here dont dither at all and with a BPM it still works out.

I also have/had dither settle issues in my AZ-EQ6 because its a little bit stiff, and the solution was to just not dither as much.

[Ouroboros]

1 hour ago, ONIKKINEN said:

I also have/had dither settle issues in my AZ-EQ6 because its a little bit stiff, and the solution was to just not dither as much.

Yes, so have I with the same mount, but not with my AM5.  

[Icesheet]

16 hours ago, Elp said:

Something I haven't suggested, which might be the culprit which I've mentioned a number of times in other threads, late last year, early this year I updated to the 2.0 asiair app version and it contains the appropriate firmware updates to the airs. My once workmanlike asiair pro suddenly became as useful to AP as a brick, I also had issues with my mini. I wasted so many sessions trying to find out the issue as it would usually be something different every time causing an end to the session but the often ones were it'd fail plate solving after the second iteration try then slew the telescope in a kamikaze dive towards the ground and the tripod, sometimes stopping responding to commands full stop, turning sidereal tracking off by itself mid plan, and the one similar to yours, after dithering it'd kamikaze again and the next two to three subs would be star trailed before it decided to recentre and star again, then do it again after the next dither and so on. It was related to the sidereal turning itself off as far as I know so obviously you'd lose your guidestars.

Solution? Well I was lucky enough to have an old beta asiair app version on an old phone, this is important because when you roll back the airs firmware, connecting back to them with the old app doesn't force update a firmware installation because it doesn't have one. So I'm using the factory firmwares on all my airs. Haven't had a single problem since.

 

Thanks, I don’t think I have any back up software and I haven’t experienced any of the other issues you mentioned but I’ll keep an eye on it. 

 

15 hours ago, ONIKKINEN said:

You can safely drop the dithering rate to something like once every 20 minutes if you have one of the newer cooled Sony sensor cameras (not sure about others). You will want to calibrate with a bad pixel map in that case, as hot pixels could otherwise remain in the stacked image. Think i recall reading that some imx571 users here dont dither at all and with a BPM it still works out.

I also have/had dither settle issues in my AZ-EQ6 because its a little bit stiff, and the solution was to just not dither as much.

I use the IMX571 so I’ll look into that. If I can limit the dithering it’s going to make a huge difference. Thanks!

I’m going to look into the power supply issue with the RST135 to see if that may be contributing. 

[fireballxl5]

 

1 hour ago, Icesheet said:

I’m going to look into the power supply issue with the RST135 to see if that may be contributing. 

I've had my RST-135E for 2 years now and although I've never dithered with this mount (at least during an imaging run🙃), I have found that this mount needs:

1) a good stable power supply,  >12V. I usually dedicate a small Tracer LiFePO4 battery just for the mount

2) a rock steady base if imaging at high ish resolution,  say <1.5"/pix. I've found that light-weight, collapsible ali tripods aren't solid enough if the mount is carrying 8-9kg of imaging gear (without a CW of course😉) and there is some movement.  These are the kind of tripods I've taken abroad for less demanding imaging. For my RC6/ASI533 combo I now use a re-purposed AstroTrac pier that has very little movement as the scope tracks across the sky. It would be nice to have a more manageable carbon fibre tripod if I could be sure it was sufficiently stable. 

HTH,  Andy

[Icesheet]

On 22/11/2023 at 11:43, fireballxl5 said:

 

I've had my RST-135E for 2 years now and although I've never dithered with this mount (at least during an imaging run🙃), I have found that this mount needs:

1) a good stable power supply,  >12V. I usually dedicate a small Tracer LiFePO4 battery just for the mount

2) a rock steady base if imaging at high ish resolution,  say <1.5"/pix. I've found that light-weight, collapsible ali tripods aren't solid enough if the mount is carrying 8-9kg of imaging gear (without a CW of course😉) and there is some movement.  These are the kind of tripods I've taken abroad for less demanding imaging. For my RC6/ASI533 combo I now use a re-purposed AstroTrac pier that has very little movement as the scope tracks across the sky. It would be nice to have a more manageable carbon fibre tripod if I could be sure it was sufficiently stable. 

HTH,  Andy

I imaging at 1.94”/px with <5kg on the Sightron carbon fibre tripod so I don’t think tripod stability is the issue here. At least it shouldn’t be. I do have a Berlebach uni tripod I could test. The power supply is something that keeps coming up so I should definitely check that out I think. How is your guiding with the RC6?

[900SL]

The harmonica mounts, if unbalanced, will transfer a lot of torque into the mount. Needs to be rock solid, I'd say. 

[Elp]

They do but the HDs are designed for such applications. Most manufacturing robotics such as ABB and Kuka use HD drives in their robot arms.

If anything a large payload could tip the tripod over, it's always wise to slew east and west past the meridian to check before leaving it unattended.

Edited November 28, 2023 by Elp

[ollypenrice]

This may come as a surprise, but I have never dithered.

Caveats:

I've only ever used cooled cameras.

I've never bust a gut to finesse polar alignment, though, in the CCD days, it needed to support 30 minute subs.  Now it only needs to support 3 minute subs.

Given the short exposures needed by CMOS, and their tiny pixels and low read noise, won't a small polar alignment error provide any dither that your system actually needs? If it really needs any at all?

I would forget the clamour of the orthodoxy and received wisdom and just try not dithering and getting more good subs.

Olly

[Icesheet]

 

13 hours ago, ollypenrice said:

This may come as a surprise, but I have never dithered.

Caveats:

I've only ever used cooled cameras.

I've never bust a gut to finesse polar alignment, though, in the CCD days, it needed to support 30 minute subs.  Now it only needs to support 3 minute subs.

Given the short exposures needed by CMOS, and their tiny pixels and low read noise, won't a small polar alignment error provide any dither that your system actually needs? If it really needs any at all?

I would forget the clamour of the orthodoxy and received wisdom and just try not dithering and getting more good subs.

Olly

You know, I actually haven’t even compared to see if dithering has made a difference in my images. In the main I’m dithering for drizzle integration in PixInsight but I haven’t checked the difference between a drizzled and non drizzled. I really should but just accepted the general consensus that it was worth it. 

I think a small polar alignment error may not provide enough random movement to replicate a true dither but I’m no expert either. May be time to make a comparison of what I have!

 

[Ouroboros]

18 hours ago, 900SL said:

The harmonica mounts ……

I’ve got one of those. I’ve never managed to get a sound out of it. 😄 😉

[Ouroboros]

I started dithering back in the day when I used a DSLR.  I clutched at it as an alternative to taking darks, which seemed such a waste of good imaging time. I never missed taking darks. The data seemed to benefit from the extra data gathered and I just assumed dithering was helping. Now with cooled cmos I suppose I’ve just carried on with the dithering out of habit, plus I use a library of master darks taken during non-imaging time.   I guess dithering looses me a bit of time per sub, but not much so I carry on with it. However, I haven’t had the problems the OP has. 

[tomato]

I had some problems with walking noise when I first used CMOS cameras so I started dithering but when I set up a dual rig the time I was losing to the operation was horrendous. 
So I stopped dithering and didn’t notice any problems, I had moved on to more recently introduced CMOS cameras by then.

[Tomatobro]

Same as Olly.  I stopped using dithering because the image creeps over long sessions and is never in exactly the same place from night to night.

But again like Tomato I use CMOS now.

There are many things that get repeated so often that they take on the status of fact. Does no harm to try things out and if it works and saves time all to the good. If not you can always go back a step.