Driveless Tracking with Sequator

November 2020

Murphy's Law: You search the internet, find nothing, create your own software to de-rotate the sky, then Alan Dyer replies "Interesting. Have a look at Sequator."

In my brief and nonexhaustive use, this is my summary of this (Win only) free software (https://sites.google.com/site/sequatorglobal/):

Sequator (or my own derotator) is NOT a substitute for a small tracker for the sky. While it does output a tracked sky with "frozen" ground in under 5 minutes, motorized tracking gives much better signal, much less noise. But for computer wallpaper or a 5x7 print Sequator is quite decent! Use it for those places you can't easily go back to reshoot with proper technique. Avoid choosing this over the superior tracking method just because it is a little easier.

Recommendation: go for it! If you're just starting out it's a great way to dip your toe in the water before committing deeply. Fortunately most of the skills and knowledge you pick up here are transferable to a higher end setup.

The developer Yi-Ruei Wu wanted to make it as simple as possible while still being powerful. While there are some sliders you can adjust, or boxes to check, the rank beginner can drag and drop a dozen jpgs (without flats/bias/dark frames) onto the main window, click on a few buttons, and enjoy results in 3 or 4 minutes!

Drag and drop darks (labelled here as "Noise") and flats (labelled here as "Vignetting") all as JPGs if you wish to be obtuse, though RAW of course will make the final image better. Nothing beats proper shooting and on-site calibration! For that amazing night in Jasper 6 years ago when you only took JPGs and didn't know better, you can get away by making flats today and guessing at the temperature and taking darks in the fridge.

Key functionalities:

• aligns and stacks the stars, then overlays a non-blurred foreground

• removes satellite/airplane trails, hot pixels

• removes distortion effects of lenses, mitigates "dark corners"

• does a decent job at removing light pollution effects

Experts remind us a lot (we seem to forget a lot) that stacking does not eliminate noise, it only reduces it. Also, one 10-second exposure is significantly better than ten 1-second exposures, and similarly two 60-second shots are much better than twelve 10-second images.

While you are considering which tracker to get, shoot away! Here's video on how to image the Andromeda Galaxy with only a camera, lens, & tripod[https://www.youtube.com/watch?v=pXcRKoxTPVg&t=2866s], by taking several hundred one-second exposures. This too works enough to "get away with it": a nice computer wallpaper image, but an 8x10 print will likely reveal underlying issues.