Aug 16, 2011

The North American Mosaic

As a member in good standing of the Saguaro Astronomy Club I've long vowed that if somebody asks me to give something back to this wonderful hobby chronic obsession in a way that might benefit someone else - that I would always say yes.  One of the great things about amateur astronomy is the general willingness of most people involved to share their knowledge in an effort to help the other guy.  One of the reasons that I write this blog (haphazard as it may be) is in an effort to share what I learn with a wider audience if anyone should be interested.  Each August our club has a meeting where all of the speakers are club members giving shortish presentations on the topic of their choice.  When I was asked to be one of the presenters I immediately agreed to the task even though I had no idea what I could talk about for 10 whole minutes beside myself - and audiences tend to find the subject of me to be an underwhelming one at best. 

A normal night at Fredericksen Meadow.
After pondering the possible topics for a few days I decided that I would cover the capture and processing involved in creating a CCD mosaic.  Never mind that I'd never actually even tried to do one myself. Nothing helps get the juices flowing better than a little bit of pressure, even if it's self-induced.  This was back at the end of June just after the new moon weekend.  No worries on my end though - I still had all of July and part of August to capture the data, create a mosaic image and put together a 10 minute presentation.  All I needed was a little bit of dark sky to capture the data.  I was confident that I could do the rest without too much trouble.  I planned a trip out in the middle of July solely to capture the raw data, but the Arizona monsoon season had other ideas and the weekend was clouded out.  Since I live in such a dry climate I immediately made plans to head north to my favorite observing site for the weekend with some friends in the cool pines and 7000' of Fredericksen Meadow in North/Central Arizona.  Three nights in the cool pines and I literally never even took the telescope out of the truck because it didn't stop raining and storming long enough to set up.  Shut out.  Again.  Not for loss though, it was a wonderful weekend hiking and hanging out with my astro-friends and just generally loving how awesome I have it in this life and how little I've done to deserve it.  Now I was beginning to get nervous.  I had only one weekend left to capture data - process the data - and be ready to present it the Friday after that. 


I casually threw out a comment to my friend Chris that I was thinking of a trip to the club's Antennas site to capture the data as he and I both live in advantageous locations for easy access to this dark sky site.  However - and you knew there would be a 'however' - it's in the western part of Arizona in the low desert at the end of July.  It is not uncommon for temperatures to sprint right past 110ºF early in the day and stay there until well after dark.  My last time there - on March 31st - it hit 102ºF and it was blazing hot for such an early spring day.  But I digress.  Other club members told us we were crazy.  I heard rumors that there was a collection taken up to have our heads examined.  Since no one has approached us, I'll assume that nobody contributed. 
The 11" Edge HD and Hyperstar on a previous trip
to the Antennas site.
We made plans to arrive just after sunset and use the first couple of hours with the first quarter moon to get set up for the evening on this one night trip.  It was genius.  The Arizona monsoon couldn't have cooperated better.  The temperature when I arrived 5 minutes after sunset was 98ºF with 11% humidity and a slight breeze.  It was warm for sure, but comfortable.  By the time I completed setup and was ready to begin imaging at 9:30pm the temperature was down to 80ºF.  Chris and I enjoyed about 6 hours of imaging and observing in shorts and t-shirt weather under a beautiful mag 6.5 sky.  Using the Hyperstar rig I was able to capture 4 hours worth of data at f/2 on the North American & Pelican Nebulas to construct the mosaic.

To make a long story short, I constructed the mosaic and I was very happy with the result as shown above.  My presentation itself didn't go as well as I'd hoped.  I made the mistake (common with me) of trying to condense what was easily 45 minutes worth of material into ten.  I was really pleased to show off how I'd processed the image in Photoshop and had a series of slides that walked through the process.  The actual work in Photoshop went quite quickly so I put together a video-walkthrough of the steps that I took for some of my fellow club members who'd been asking me questions about my own workflow.

NGC 7000 and IC 5070 Mosaic (North American & Pelican Nebulae)
4 frame mosaic - 24 exposures - 2 minutes per sub exposure
Captured with a QHY8PRO CCD Camera
Celestron 1100HD Telescope with Hyperstar @ f/2 on a Celestron CGE Mount
 To make a long story short, I constructed the mosaic and I was very happy with the result as shown above.  My presentation itself didn't go as well as I'd hoped.  I made the mistake (common with me) of trying to condense what was easily 45 minutes worth of material into ten.  I was really pleased to show off how I'd processed the image in Photoshop and had a series of slides that walked through the process.  The actual work in Photoshop went quite quickly so I put together a video-walkthrough of the steps that I took for some of my fellow club members who'd been asking me questions about my own workflow.

It's just shy of 10 minutes a straight, unedited walkthrough that shows everything that was done in Photoshop to process the images after they were calibrated and stacked in Maxim DL.  I've added the video here too for anyone that might get some benefit out of it.  A couple of notes about the video:
  • There is no audio track in the video.  I simply hit record and did a walkthrough while Camtasia captured the screen for me. 
  • In the first step you'll see that I run an action against all 4 frames that isn't really shown.  That action is simply a curve followed by four iterations of levels that adjust the gamma slider.  I did this via action so that I could insure that all 4 frames were initially stretched with exactly the same settings.  There is no hidden voodoo there - and the later iterations of levels are all done in the same way.
  • Since I'm not sure how well this video is going to get mangled by the compression algorithms, Here is a link to a full Windows Media version.  It's a 21MB file, so you may want to download it before attempting to watch it.
  • The video does go through the steps pretty fast.  The pause button is your friend if you're trying to follow along and try any of it yourself. 
video