Taking Stock – The Software

Last time out I covered the hardware, which looks all pretty and imposing when it’s all setup – but it’s exactly half of the equation.  It’s the software that makes modern astrophotography possible.  In my own setup, the software plays a critical role in every step of the process from setting up to publishing a finished image.  In this second installment I’ll finish detailing the pieces of my imaging rig that all contribute to the end result and how it all fits together.  From this point forward it’s my hope that I can start tackling some specific tasks and how I handle them when it comes to deep sky imaging. 

PEMPro-V2

PEMPro is designed to a do a handful of things – chief among them is to measure and program periodic error correction on a telescope mount.  It excels at this task and I had excellent results using it on both of my previous mounts.  On my original Celestron CGEM I had a native periodic error of 17.6” peak to peak.  A couple of hours with PEMPro and I was able to program the mount with a curve that reduced it to 3.1”.  It helped me similarly in taming my Celestron CGE (52.1” down to 4.3”).  As I detailed in the last post, my Astro-Physics AP900 has a native periodic error of 1.45” peak to peak.  I haven’t bothered to even try and improve that yet.  Interestingly, Astro-Physics uses a specialized version of PEMPro to measure and program the periodic error in their mounts prior to shipping them out. 

For me though, PEMPro’s greatest strength is in the Polar Align Wizard that is another of its functions.  I don’t have a permanent observatory so I’m setting up and aligning the equipment every time I go out to image.  I’ve managed to arrange my imaging rig and the setup workflow in such a way that I can be polar aligned well enough for 30 minute sub-exposures before the end of twilight.  PEMPro’s Polar Align Wizard is a huge part of that.  Essentially, it’s a computerized version of drift alignment that works as follows:

• A quick routine is used to determine the camera’s orientation (position angle) and the calibration of North/South/East/West to the X/Y coordinates of the camera chip.  Typically this takes me about 2 minutes. 
• PEMPro will measure a star near 0º declination and near the meridian by taking repeated subexposures and measuring the star’s drift over a period of time.  Typically, I do this for 7 minutes.
• After selecting a star in the star field, PEMPro will draw an arrow and a circle over the frame and begin taking repeated images of the field.  Using the azimuth adjustment you simply adjust the mount east/west until the star is in the circle drawn. 
• Altitude is then set by moving 45º relative (east or west) to the meridian and repeating the 7 minute measuring phase. 
• After selecting a star in the star field, center it in the superimposed circle using only the altitude adjustment on the mount.
• Repeat if necessary.

It’s that simple and takes about 20 minutes.  Typically I’m starting this process as soon as any star bright enough to see naked eye appears near the meridian and 0º declination.  As I mentioned, I’ll write a post on my entire process some time in the future.  My method gets my polar alignment to about 1 arc minute from the celestial pole before the end of astronomical twilight and a big part of that is due to PEMPro. 

Maxim DL

Maxim DL is one of those suite software appllications that tries to be all things to all people and it does a pretty good job of it.  Nearly everything that has anything to do with data acquisition goes through Maxim DL in my setup.  I use Maxim DL to control the telescope and the camera through every phase of capturing data.  I use Maxim DL to:

• Align the telescope at the beginning of the evening. Using the built-in PinPoint LE astrometry software after polar alignment I can sync the telescope to a plate solved field and I’m done.  Ready to slew anywhere in the sky.
• Slew the telescope.  Using the built in catalogs I’ll slew the telescope to the chosen object.  An automated exposure is taken after a slew and plate solved to ensure that I’m exactly centered on the field.
• Focus the telescope.  Sort of.  I use Maxim DL to tweak the Moonlite focuser during a filter change to the appropriate offset for the filter being selected.  Real focusing chores are handled by FocusMax – which uses the camera control in Maxim DL to do it's thing.
• Guide the telescope.  I use Maxim’s built in guiding capabilities to autoguide during subexposures. 
• Full camera control including temperature regulation, switching filters, taking exposures and moving the telescope slightly to dither between exposures. 
• Capture of calibration frames.  Dark, bias and flat frames are all taken with Maxim DL.  Soon I’ll be working to configure Maxim to automate flats through each filter using an Optec FlatMan.  Stay tuned for more on that.
• Maxim DL does an excellent job of controlling the telescope to correctly capture the multiple frames needed for a mosaic. 
• I use DDP in Maxim DL during an evening just to preview what kind of data I’m capturing.
• Maxim DL has many other built in features for calibrating, stacking and processing images.  While they’re effective I have found that there are other tools that I like better for those tasks. 

PixInsight

PixInsight completely changed the way that I process images.  It’s software developed by astrophotographers specifically for the purpose of processing astrophotos.  It has gotten a bad rap by people who haven’t thoroughly investigated the product saying that the learning curve is steep and that educational resources are lacking.  I’ll agree that it’s a different approach to processing than most people are used to, but if you take the time to use the resources that are available it’s quite intuitive.  I use it for nearly all of my calibration, stacking and image processing.  The 800 pound gorilla known as PhotoShop still figures in to my image processing scheme for some final tweaks, but 95% of my workflow after I capture an image is done with this application.  I use it to:

• Create master bias, dark and flat frames.  Here’s a tutorial on the creation of master calibration frames.
• Calibrate, Register and Stack a series of light frames.  It takes more effort in PixInsight than in other applications but the end result is a much cleaner master light frame in my experience.  I stopped using Maxim DL’s calibration & stacking routines after the first using PixInsight’s methods just once.  
• All image processing tasks including color calibration, background neutralization, stretching, contrast enhancement and teasing out detail in the image.

Expect to see some more entries into this column detailing various aspects and techniques that I use in PixInsight.  Meanwhile, if you’re interested in learning more there are abundant resources on the web.  Start at the PixInsight website.  Many tutorials are there.  Also, go to Harry's Astro Shed and start there.  I learned to process an image by taking one of my own and just walking through Harry’s tutorials.  I haven’t personally seen them myself – but I know that Warren Keller and Rogelio Bernal Andreo are working on a tutorial series at IP4AP.  I’ve seen the Photoshop series that Warren did and it is an excellent resource.  M81 and M82 shown below was the first image I processed in PixInsight. 

 

PhotoShop CS5

The heavyweight of all image processing packages is without question Adobe’s PhotoShop.  I once used it for everything I did in a stacked image but it has fallen very much by the wayside since I picked up PixInsight.  In all fairness though, I do still use it at the very end of my workflow to do some final background smoothing, perhaps an Unsharp Mask and to resize/save the image for publishing on the web.  There are a lot of resources available to learn how to process an image with PhotoShop.  I found Adam Block’s DVD “Making Every Pixel Count” to be the best among them.  I’ve since met Adam and had an opportunity to pick his brain on a couple of things.  He’s a gracious guy who’s more than willing to share his extensive knowledge.  Check out one of his imaging workshops if you want some hands on experience with him.

What’s Missing?

If I had to go through the rest of my life with just the equipment and software that I have I could still die a happy man.  I don’t think that I’m missing any critical piece of the puzzle any longer.  But let’s face it – astrophotographers are probably the most desperate breed of astro-equipment junkies out there.  Now that I have a narrowband imaging rig and could conceivably image every clear night from my backyard it appears that imaging could become a threat to sleep and my ability to conduct what normal people call a normal life.  I’ll evaluate the situation before long and see if it makes sense to incorporate an automated imaging platform to handle imaging sessions for me.  I’ve been quietly eyeing CCD AutoPilot to fulfill that role but I’m not a point where I’m ready to seriously take on that task just yet.

With new moon coming tomorrow I hope that the Arizona monsoon cooperates enough to allow me a solid first light with the SBIG ST-8300 and filter wheel this weekend.  Once I get that incorporated into the workflow then I’ll see about the last couple of “nice to have” pieces – an off axis guider and an automated imaging platform.  Until then,  I continue to be a happy guy who has it far better than he deserves it.