Astrophotography: Accidental capture of Orion

 

This image is the result of stacking only 18 light frames of 5 seconds each with no tracking mount installed and using Sequator with no other post-processing during a full moon.  Let's break this statement down.

Happy Accidents

My original intent was to test the ASIAIR Pro software and see what it can do.  The first thing I did was to put my camera, an unmodified Canon EOS T800D with a 50mm Lens, on a camera tripod.  I pointed it at the brightest objects in the sky that was also near the back door to the garage because it was below freezing outside and I wanted to be able to warm up.  It turned out that object was Orion.  It was conveniently placed between my pine tree and the garage eaves.

A Bit Blurry

Focusing was the first issue. What I discovered was that setting the exposure length long enough to get a good star image was a trade-off with how quickly the image could be transferred from the ASIAIR Pro back to my cell phone that was running the ASIAIR software.  This trade-off is important because once I turned the focus dial, I had to wait.  I was originally doing this in Preview mode and eventually switched to Focus mode.  This is going to require some additional fiddling.  My suspicion is that I need to do the coarse focusing using the image on the LCD screen of the camera before using the ASIAIR software. Unfortunately, I have something setup that doesn't allow me to see the image on the LCD screen.

Long Must I Wait

The second issue I had was the exposure length.  There is a rule-of-thumb formula called the "Rule of 500" to determine the useful exposure length before star trailing starts to be noticeable.  A star trail will make the stars look like short lines instead of round objects.  For my setup this night, the 500 rule translates into 500/50 = 10 seconds.  Wait, there's more.  My camera has a crop sensor, the light hits a larger area than the actual sensor so my image is cropped.  The crop sensor is rated at 1.62 which now means that my effective focal length (really my field of view - FOV - is narrowed as though I had a higher focal length) is 1.62 times higher.  The 500 rule now says 500/(50*1.62) = 6.17 seconds.  My camera has a setting at 5 seconds so I used that.  This is also another area to work out to see the effect.  For example, compare 5 seconds to 10 seconds.

It Just Sits There

I didn't plan to take any real useful images and I didn't want to add the complexity of my star tracker into the fiddling session.  A star tracker would rotate the camera at the same rate as the earth rotation to keep the stars in the same position of the image sensor.  The star tracker would also mean that my exposure lengths can increase, breaking the 500 rule.  However, the full moon would still be the big issue since the gutter would become easily the brightest part of the image.

The top image is the first captured image using the ASIAIR's Live Mode.  There is a checkbox to click in the software to save every captured image during stacking.  I'll describe stacking in a later post but essentially it means taking multiple images, align based on the stars the software sees, and then add them together to increase signal and reduce noise.  The bottom image is 18 images later, right around 2 minutes later.  Looking carefully, you'll notice that Orion is now closer to the gutter of the house and the moon has changed position which changed its shadow.  This proved to be a problem with Live stacking and it eventually had issues especially during the last 8 images where Orion mover to the very edge of the gutter.

And Then It Happens

What surprised me was that I actually did get a reasonable focus and I also can see some detail of the Orion Nebula as shown in a zoomed in section shown below.

The full moon also presented an issue. It was low on the eastern horizon so it was lighting up the side of the house.  In the above images, you'll see how it's lighting up the gutter.  It is also adding a weird glow to the sky. 

The other thing I learned is image handling.  The ASIAIR Pro saves images in the .fits format which makes using some software a challenge.  For example, Sequator doesn't natively handle FITS files so I had to convert the files to TIF.  I had to find a converter for that.  I used the ASIFitsView in the PC software ASIStudio.  Unfortunately, it is a very labor intensive task of conversion.   I also tried FITSLiberator but that doesn't have a batch convert either.

Sequator was really easy to use and allowed me to set the tree and the house roof as a static image which was really cool.  I tried stacking all of the image and let the tree and roof blur (the stars stay fixed in the image and the formerly static parts of the image move) but didn't like the look.

Where Do We Go From Here

So my journey is on.  I've learned a few things:

• I need to streamline focusing
• Set up and execution of the star tracker needs to be tested
• Work on capturing dark, flats, and bias frames for improved image quality
• Figure out an efficient method of handling images and format changes
• Work out why some softwares don't seem to retain the color information from the camera
• Work on placement of my wifi extender to not drop coverage during an acquisition
• Work on procedures for acquisition and phases of the moon
• Work on image postprocessing in Sequator and GIMP