NGC 5907 was first discovered by William Herschel in 1788.  It is also known as the Splinter Galaxy (and sometimes the Knife Edge Galaxy).  It has a morphology classification of a type SA(s)c seen almost perfectly edge-on.  It lies at a distance of 53 +/-8 Mly and has an apparent magnitude of 11.1.  At 12.7' x 1.4' it is a moderately large target suitable for most amateur telescopes.  NGC 5907 is a part of a larger group of galaxies called the NGC 5866 group and it has few detectable blue giant stars.  In 2006, a team of astronomers discovered an extended tidal stream surrounding the main galaxy.  It also contains an ultralumious X-ray source.

This image was taken with my 20" system using a new QHY600M-ph CMOS camera.  That makes it the first image that I've processed from a CMOS camera so it shouldn't be too surprising that I learned a few things along the way.  In general, I really like this camera!  It has zero amp-glow and the raw images appear to be every bit as clean as what I get from my ML16803 cameras.  Interestingly, the CMOS camera is MUCH less susceptible to cosmic ray strikes.  I've known that about CMOS cameras, but I've never really completely understood why.  As everyone knows, the big operational change in going to CMOS is in setting the gain and offset values.  For this image I picked a gain of 28 (to be near to unity gain).  I don't remember the exact offset value but I might have been around 30.  Whatever it was, it's a bit too low because I found a few pixels with zero values and that's no good.  I'll raise it a bit for my next effort.  

The other big difference between this camera and my FLI cameras is in the cooling system.  The FLI cameras generally have a MUCH more powerful cooling system!  I originally set the set point at -15C and as soon as the weather warmed to over about 19C, I couldn't reach the set point and that played havoc with my calibration files.  Don't get me wrong: Maintaining a deltaT of -35C is respectable performance but that's about 10C less than what the FLI cameras will do.  I just need to be more careful to plan an appropriate temperature when it's warm.

I took the Lum data for this image binned 1x1 and the RGB data binned 2x2.  I did two processing runs one at 1x1 and one at 2x2 and in the end the 2x2 effort won out.  The noise was lower all around and I could see ZERO difference in detail.  That makes sense for this data set because the seeing conditions rarely got better than about 1.7" and the median turned out to be only slightly below 2".  This all jives with my theoretical analysis showing that the benefits 1x1 binning on this scope don't show up until you get well below 1" seeing conditions.  The file size for 1x1 images is gigantic so it makes sense to use 2x2 binning for all but special cases.  (Once you have a 1x1 binned image in PI, a single XISF image takes up 246.7 MB.  Whew!)

My site at the Bend airport is pretty dark over much of the sky but it's problematic in terms of gradients.  The airport beacon runs all night and it's easy to see it sweep through the sky--every minute.  I suspect that's one reason why I struggled with gradients in this data set.  The other problem is that Bend and Redmond illuminate the sky with light domes of various sizes.  I could easily see the extended tidal stream in my stacked data but extracting it cleanly from the gradients was nearly impossible.  I've included a highly stretched inverted image so that you can see the tidal stream on one side of the galaxy.  The opposing stream was lost and probably obscured by applying DBE to the data.  I wasn't really trying to show the stream so I didn't worry about it.  You need pretty dark skies to really go after the streams--and I've seen a few images on AB that clearly show the streams--so it's doable.

The inverse, tidal stream image emphasizes something else about satellite trails that I'm only now appreciating.  In spite of all the discussion about StarLink, I've generally shrugged it off thinking that it's a problem that stacking filters will take care of.  Well...not so fast!  Stacking filters do easily take care of satellite trails...when they are bright!  The problem becomes more severe with the newer blackened satellites that don't reflect as much light.  They still create faint trails but now you have to set the stacking filter limits much tighter to completely eliminate them--and that screws with the statistics of the stack, which ultimately results in a noisier image.  I wound up splitting the difference and clone stamping out the very faint remaining trails.  I hate doing that but those faint remaining trails are tough to deal with--and there were a fair number of them.

Finally, I'm all set to ship the 20" sometime in late September and I've still got a handful of little issues to resolve.  I've also started on a new project to learn to fly helicopters, which means that I can't stay up half the night to image before I fly.  In the meantime, the monsoons are in full swing in New Mexico so my 14" has been unusable for over a month with no end in sight.  Even my refractor project is dead in the water waiting for parts that no one can ship.  The bottom line is that my imaging activity is going to get dialed back for a while.  I've got another equipment post brewing but I may go radio silent for a while until I can get back to imaging.  I've got a great talk brewing for AIC in the Fall so hopefully I'll see a bunch of you there!

Whew...this is a long one!  Anyway, let me know what you think.  As always C&C is welcome and appreciated.

- John