Re: [ap-ug] [ap-gto] Hydrogen clouds of the Bubble Nebula

Roland Christen

Nothing says that you have to do 1 hour exposures. I do it for test purposes and because I can. My 160 refractor can take some temp changes without changing focus. If your scope is more finicky, then take shorter exposures and stack 'em.

Your 1100 mount is fully capable of unguided imaging with modeling, as well as hybrid imaging with modeling and nudge guiding.


-----Original Message-----
From: dvjbaja <jpgleasonid@...>
Cc: <>
Sent: Wed, Sep 9, 2020 12:11 pm
Subject: Re: [ap-ug] [ap-gto] Hydrogen clouds of the Bubble Nebula

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. 


On Wed, Sep 9, 2020 at 10:04 AM uncarollo2 <chris1011@...> via <> 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.


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