Summary

The Deer Lick Group and Stephan's Quintet in Pegasus form a beautiful collection of galaxies and present a welcome challenge to any imaging system.  This image was acquired using my TS RC10 and QHY600M over a few rare, moderately clear winter nights, but with at best mediocre seeing conditions.  This time of year, however, one needs to take whatever semi-clear opportunities arise in between the clouds, rain and snow.


Deer Lick Group and Stephan's Quintet

I've imaged this scene in the past and written an earlier description of the objects that I shamelessly copy (and edit) here:

According to Wikipedia and the Concise Catalog of Deep-Sky Objects, the Deer Lick Group contains the larger unbarred spiral galaxy NGC 7331 (Caldwell 30) and members NGC 7335, 7336 (lenticular or unbarred spirals), 7337 (barred spiral), 7340 (elliptical). The latter are often referred to as the "fleas". NGC 7331 is about 40 Mly distant, and its "companions" about 332, 365, 348, 294 Mly distant, respectively. Its apparent size is about 10.2' x 4.2' with magnitude 9.8. NGC 7331 is often called the Milky Way's twin as it is similar in size and structure, although the Milky Way is more recently thought to be a barred spiral. NGC 7331 is notable for having a retrograde rotating bulge.  Refer to Revision E to see an enlarged, yet disappointingly blurry image.

Edouard Stephan discovered the quintet of galaxies in 1877. Four of the galaxies form the first compact galaxy group ever discovered, called the Hickson Compact Group 92. These will likely merge with one another in the future. There is a filament that lies in the regions between the galaxies, most visible in green (although not really visible in this image), that results from a shock wave formed by one of the galaxies falling into the center of the group. The three larger, tightly-grouped galaxies are NGC7319, NGC 7318A, NGC 7320. NGC 7317 is the nearby outlier to the left of this tight group of three. NGC 7320C is to the right of the main three. They vary in magnitude from 13.9 to 16.7. These are roughly 300 Mly distant, although I was unable to find more precise values than that.  Refer to Revision F to see an enlarged, although limiting resolution and seeing-challenged image.


Equipment and Field Notes

This past year I accumulated new hardware, and this was my first session that brought together most of the new equipment intended for longer focal length imaging.  The Teleskop Services 10" RC is a truss scope with quartz glass mirrors and advertised to have 99% reflectivity on both.  Years ago I used an 8" RC but ran into many of the common collimation issues.  With the old 8" tube format, I was frustrated that the focuser and camera were mechanically linked with the primary mirror, and this made collimation an overly complicated process.  The truss version isolates the primary mirror adjustments from the rest of the scope, and I have found collimation to be much easier.  I use a Takahashi Collimating Scope for initial steps followed by star collimation.

I used a field flattener (TSRCFlat3) to correct the image, and I am mostly pleased with the outcome.  Some additional fine tuning of the spacing is in order, but I got it close here.  Earlier images with this scope and without the corrector had severe aberrations at the corner, but this has now been mostly mediated.

This past year I acquired a QHY600M-PH CMOS camera, and I must say that I am both pleased and impressed with it.  One thing I've run into is that, with all the modes and adjustments of gain, I haven't quite settled on how best to operate this camera.  For this image I used Mode #1, which is called the "High Gain Mode", however I find that name to be misleading.  With gain parameter setting of 0, the actual system gain is about 0.78 [e-/ADU] according to my measurements, with read noise of 3.6 [e-].  This places the full well capacity at 51,400 [e-] and the dynamic range at 14,400 [steps] or 83.2 [dB] or 13.8 [stops].  This is almost the highest dynamic range that I measured with this camera.  The newer Mode 3, called "Extended Fullwell 2CMSIT", is slightly higher.  I have not yet arrived at a precise understanding of all these options!


Processing Notes

The biggest downside I've run into with this new system is that flat calibration has been difficult.  No matter what I did, my calibrations resulted with circular shadows and light regions that appeared to mimic the secondary mirror.

After some research, I may have found at least part of the reason for this.  According to some sources, these GSO scopes (of which TS is one of the many rebrands) have a design flaw with their baffle tubes.  These are the tubes that fit down into the hole of the primary mirror through which light is focused down from the secondary mirror to the camera.  Stray light that comes in just around the second mirror obstruction can directly enter the baffle tube!  In fact, once I learned about this, I removed the camera system and looked up through the focus tube towards the secondary mirror.  There is clearly light coming in from around the second mirror housing.  In my light-polluted environment, this very likely wreaks havoc with my imaging and calibration.

I refer the interested reader to this video, which provides explanations of and solutions to the problem.  Following the findings and instructions presented in the video, I have since constructed a baffle tube extension, and I am presently devising some tests to see how it affects flats.  I also have another part on order that, instead of extending the baffle tube, attaches to the front such that the baffle tube opening is slightly reduced.  This is, like much of the world's goods at this time, still on back order.  Eventually, I'll compare the two methods.

With the calibration issues, I had to perform unpleasant and unholy things to my image to correct the background.  Following that I was able to use my usual processing steps to produce the LRGB image.  As noted above, the seeing conditions were rather poor, more so than usual, and this is the best result I could conjure from the data.

Another modification I have since made is to add flocking and flat black paint wherever possible through the baffle tube and focus drawtube.  It never ceases to amaze me just how light-colored and glossy some of these surfaces are manufactured!  I got a small amount of one of those ultra-black flat paints and used it to cover some of my surfaces.  I look forward to testing all these changes out as soon as I can.


Conclusions

The new imaging system is a work in progress, but it's slowly coming together.  I hope to eventually fix the stray light and calibration issues.  There are some other incidental pieces of hardware that have yet to arrive due to the ongoing supply chain issues, but I have enough things gathered to image again at my next opportunity.  May it come soon!

I have just learned that there is a 0.8x focal reducer / corrector available for this scope, and I will give it serious consideration.  It looks like its connector threads and back focus distance is comparable to my 1.0x corrector, so it may not require much adjustment to swap the two out as I wish.  (The madness continues!)

Thank you for your kind attention to all my notes.  I hope they may be of interest and value to some.  It is my intention to post my characterization curves of the QHY600M soon.

And Merry Christmas to all!