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Hydrogen clouds of the Bubble Nebula


Roland Christen
 

Hi All,

Just posted my new project of the Bubble nebula region. This first image is just the H-a portion to which I will eventually add OIII and SII for a narrowband color image. The exposure is 8 hours with 1 hour subs.

The mount was run with modeling on and gentle "nudge guiding" using an off-axis Lodestar guide camera. Guiding was done once every 15 seconds with 5 sec exposure times. The mount model was running in the background with custom tracking in both axes. The images were taken over 4 nights, some of which were very good seeing and some had poor seeing. On the good nights I was getting less than 0.1 RMS guide star motions and star images measuring around 1.3 arc sec FWHM.

"Nudge Guiding" is a kind of hybrid between full unguided and full guided. It has the advantage of smooth axis motions of an unguided imaging run plus the overall accuracy of guiding over long periods of time. The guide settings can be made so that only a very small guide pulse is sent to the mount every once in a while so that the mount is never being asked to chase the seeing.

https://www.astrobin.com/qq9mmt/
https://www.astrobin.com/full/qq9mmt/0/

Rolando


dvjbaja
 

Lovely shot.  The only problems I have had with 1 hour subs is temp change, resulting in focus change during the long sub-exposures or running into the dreaded "mount flip" before the exposure is completed.   Well... I have less than 24 hours to decide if I want the Mach 2.  My 1100 has been amazing, and doesn't want me looking at another woman. 

-jg

On Wed, Sep 9, 2020 at 10:04 AM uncarollo2 <chris1011@...> via groups.io <chris1011=aol.com@groups.io> wrote:
Hi All,

Just posted my new project of the Bubble nebula region. This first image is just the H-a portion to which I will eventually add OIII and SII for a narrowband color image. The exposure is 8 hours with 1 hour subs.

The mount was run with modeling on and gentle "nudge guiding" using an off-axis Lodestar guide camera. Guiding was done once every 15 seconds with 5 sec exposure times. The mount model was running in the background with custom tracking in both axes. The images were taken over 4 nights, some of which were very good seeing and some had poor seeing. On the good nights I was getting less than 0.1 RMS guide star motions and star images measuring around 1.3 arc sec FWHM.

"Nudge Guiding" is a kind of hybrid between full unguided and full guided. It has the advantage of smooth axis motions of an unguided imaging run plus the overall accuracy of guiding over long periods of time. The guide settings can be made so that only a very small guide pulse is sent to the mount every once in a while so that the mount is never being asked to chase the seeing.


Rolando


CurtisC
 

On Wed, Sep 9, 2020 at 12:04 PM, uncarollo2 <chris1011@...> wrote:
The mount was run with modeling on and gentle "nudge guiding"
I'm baffled as to how you do this.


Roland Christen
 

Nudge guiding is done while the mount modeling is adjusting the background tracking rate. Both RA and Dec axes have to move at a different rate than sidereal in order to accommodate atmospheric refraction and other effects. While the model can be quite accurate for 5 to 15 minutes time period, it might not work well enough for 1 hour exposures by itself. There will be some drifting just simply because the model points are not super accurate to the 1/10 arc second level. So, for 1 hour exposures some guiding is required if your scope has high resolution and you can record sub-arc sec detail.

In the guider screen shot below, notice that the tracking is quite good for periods of time with no guide commands going to the mount. Then as it drifts a bit beyond the Min Move setting, the mount gets a little nudge to ring it back. The nudges are very small, typically set to about 30% of the full blown command that would be sent if no background modeling was being applied. During this 1 hour imaging run shown below, the RA rate was calculated at -65 arc sec per hour and the Dec rate was +12 arc sec per hour. Almost all of the RA rate was caused by atmospheric refraction with a little bit of flexure added. If no modeling and no guiding was done, then the RA axis would have drifted by 1.1 arc sec per minute. If only modeling was used with no extra guiding, the drift in RA would have probably been around 4 to 5 arc seconds per hour (0.08 arc sec per minute).

This is the reality of imaging on a planet that has an atmosphere that you can breathe. :-))

Rolando



-----Original Message-----
From: CurtisC via groups.io <calypte@...>
To: main@ap-gto.groups.io
Sent: Wed, Sep 9, 2020 3:25 pm
Subject: Re: [ap-gto] Hydrogen clouds of the Bubble Nebula

On Wed, Sep 9, 2020 at 12:04 PM, uncarollo2 <chris1011@...> wrote:

The mount was run with modeling on and gentle "nudge guiding"
I'm baffled as to how you do this.


CurtisC
 

Oh!  I guess this is something possible under the Autosave tab, which I rarely use.  I use CCD Commander for 99.9% of my imaging, and it tells MaxIm what settings to use.  Could you get a similar result if you just used standard guiding procedures?  I realize that that's not the point of your project.  When/if I get a Mach2 (I'm on the "notify me" list), maybe I'll try something similar.   I was inspired by your Pelican images to shoot the Pelican with my own gear: 30 min subs, 5 sec guide exposures (but with immediate corrections), Mach1GTO and TEC140ED scope.  Seeing varied, of course, over the many nights to accumulate 19.5 hrs of data, but the result was pretty good.  


Roland Christen
 


I guess this is something possible under the Autosave tab, which I rarely use.
It's not under the Autosave tab. It's in the guider settings under Advanced.
The delay is after the exposure and after the guide command is sent to the mount. It delays the next exposure, it does NOT delay the commanded move. In fact, if you put a delay after the exposure and delay the move command, you will get much worse results.

What you are doing is fine. Once you start guiding the Mach2 encoder mount, you can leave your 5 second exposures with no delay in between, just turn down the aggressiveness to prevent hunting the seeing.

Rolando


-----Original Message-----
From: CurtisC via groups.io <calypte@...>
To: main@ap-gto.groups.io
Sent: Wed, Sep 9, 2020 6:30 pm
Subject: Re: [ap-gto] Hydrogen clouds of the Bubble Nebula

Oh!  I guess this is something possible under the Autosave tab, which I rarely use.  I use CCD Commander for 99.9% of my imaging, and it tells MaxIm what settings to use.  Could you get a similar result if you just used standard guiding procedures?  I realize that that's not the point of your project.  When/if I get a Mach2 (I'm on the "notify me" list), maybe I'll try something similar.   I was inspired by your Pelican images to shoot the Pelican with my own gear: 30 min subs, 5 sec guide exposures (but with immediate corrections), Mach1GTO and TEC140ED scope.  Seeing varied, of course, over the many nights to accumulate 19.5 hrs of data, but the result was pretty good.  


CurtisC
 

On Wed, Sep 9, 2020 at 06:50 PM, uncarollo2 <chris1011@...> wrote:
It's not under the Autosave tab. It's in the guider settings under Advanced.
Of course!  "Delay after correction."