M45, the Pleiades is big and it's bright and it might be the second most imaged object in the sky after the Orion Nebula.  Nevertheless, it is an interesting object with gobs of delicate blue reflection nebula surrounding a beautiful, naked eye open cluster.  For me, spotting the Pleiades signals the beginning of Fall when it first appears in the eastern sky.  Since I lost the ability to run my Hyperstar reducer on my C14 when I shipped the scope to New Mexico, I haven't had a scope that had a wide enough field to shoot objects as large as M45 for many years.  Still, it's been in the back of my mind for a long time and when it appeared in the sky while I was configuring my GTX130 refractor, I was eager to attempt another image.

Before I started on this project, I had to get my scope configured and that has turned into more of a job than I expected.  Since my last post about this scope, I replaced the FLI filter wheel with a Pegasus Indigo filter wheel.  The Indigo is a nice-looking product that turned out to be not ready for prime time.  I've written elsewhere about all the problems so I’ll only briefly summarize them here: 

1) The unit I received required special parts to seal the housing against dust.  The folks at Pegasus kindly sent the parts as soon as I pointed out the problem.

2) The filter mounting system using screws and washers is just lame.  I had to 3D print filter retaining caps to fix the problem.  Unfortunately, my first attempt to get the parts printed from the factory supplied STL file resulted in parts with the wrong dimensions.  I had to file them down to get them to fit and I’m still dealing with the fact that the filters rattle in the carrier.  Customers should NEVER have to resort to fixing stuff like this on a new product right out of the box!

3) The series of slots and holes in the relatively thin FW cover weaken the structure so much that it flexes under the weight of the camera.  This means that camera tilt alignment changes slightly depending on what side of the meridian the telescope is pointing.  I’m still trying to determine if the flexure is small enough to be acceptable.

4) I ultimately realized that no matter what I did, finding a clean way to shim tilt out of my camera wasn’t possible—particularly since the scope is supposed to ship to Chile.  After I took this image, I finally broke down and installed an Ocotopi tilt adjuster to deal with the problem.  Using the FWHMEccentricity tool in PI, I was able to reduce FWHM variation across the field to less than about 0.2 pixels.  I didn’t have the patience to try to perfectly adjust the spacing to completely eliminate astigmatism in the extreme corners of the field but I try not to let perfect be the enemy of good enough.

5) I still can’t get the Indigo to connect to SGP when I power up without having to physically disconnect and reconnect the USB cable.  That’s a show stopper that I’ve got to solve before this scope can ship to Chile.

For this image, I simply bolted the camera to the FW and measured the sensor tilt.  I could see that one corner was high so I guessed and added a shim made of three layers of Scotch tape.  Of course, I picked the wrong corner but once I swapped my tape shim to the opposite corner, it was almost spot on!  That’s how this image was taken.  My concern about sending a tape shim to Chile was that if anything needed to be replaced, I’d never be able to talk the observatory techs through a repair.  So, I ordered the Octopi adjuster.

We’ve had a long string of warm clear early Fall nights in central Oregon and that was perfect for getting the scope aligned and for gathering some “real” data.  Unfortunately, my “backyard” is at our local airport where I run the scope on a driveway that leads into an airplane hangar.  Since it’s not a secure location (with no commercial traffic, our little airport is one of the last in the country with NO security fences), I have to spend the night in the hangar while the scope runs.  Since I wind up staying up pretty late and since I have to get up at dawn to roll the scope in, I don’t get much sleep and that ultimately limits the number of nights that I can image before I’m completely trashed.  With an active daytime life, travel, and the lunar cycle, I was only able to spend just two full nights gathering data.  Since I hadn’t measured offsets, I simply autofocused on every frame, which seriously reduced the total throughput.  By using two-minute exposures, the system probably spent as much time exposing as focusing!   Clearly, that’s another problem that needs to be addressed.   I only tossed out about 4 frames from each channel that were ruined by passing high thin clouds and by the time I was done I only had about 5 hours of useable data.  When I took this data, the Pleiades wasn’t high enough in the sky to start imaging until about midnight, which didn’t help the situation.

Ultimately, I treated the lack of data as a challenge to see what I could pull from just 5-hours of data and this is the result.  In this case, it was all about balancing the stretch against the noise while being very careful not to introduce unexpected artifacts.  I wound up taking three runs at it before I eliminated most of the serious artifacts.  I hope that I can try again with the scope operating remotely so that I can gather 20+ hours of data.  That would make a BIG difference in producing a much cleaner and deeper result!  

The image shown here is very slightly cropped from the original 1x1 binned field that came out of the camera. To reduce the size, I've downsampled it by 50%.  The surrounding star field has been de-emphasized a little in processing to better show off the nebula.  As always, C&C is welcome so let me know if it works...or doesn't.

John