High-gain Test - Gathering Narrowband Data

September 26, 2019 - Reading time: 3 minutes

Autumn is officially here, and this is the season of the Pleiades, Orion, the nebulae in the constellations of Perseus, Monoceros, Auriga, Taurus, and Gemini. Now, M42 isn't in view until 2am, so that had to be the last in the sequence. And, yes, you can tell I was just dorking around with filters with our galactic neighbor, Andromeda M31, in near IR and hydrogen-alpha. I know M31 is a decent Ha target, and you can see some wonderful images in Ha-RGB out there in the world, but I had never tried shooting 2-minute subs of M31 with a 685nm long pass filter.  

I ran the ZWO ASI1600MM-Pro mono CMOS camera at a gain of 200 and offset of 65 in the following shots. And no calibration frames for any of these. Higher gain reduces dynamic range, but you're also reducing read noise and gaining (ha ha) resolution and the ability to shoot shorter exposures--and more of them, and if you take enough subs, this should balance things out.  There are miles of discussion on gain and offset in astro-imaging, but I was recently reading Jon Rista's comments in an astrobin forum thread and that got me to test out higher gain/offset. 

M31 in Near-IR + Ha

I moved over to Cassiopeia and shot 40 x 4-minute subs each of IC 1805 (Heart Nebula) and IC 1848 (Soul Nebula) in Hydrogen-alpha. Here's the stitched together pair:

Still waiting for Orion to get above 30°, I spent some time on NGC 1499 "California Nebula"

And Orion is back in the sky! Sure, you have to get up at 3 in the freakin' morning to see it with your own eyes. Or you can program your astro imaging system to stay up all night and take pictures without you. Here's M42, Orion Nebula, along with M43, De Mairan's Nebula--that's the spherical-looking cloud formation with the big bite taken out of it. And above that, shining brightly, Sh2-279 Running Man Nebula--although the famous running man shape isn't clear in hydrogen alpha. I'm not sure how well it comes out with oxygen III and sulfur II, but I'll come back another night to capture the OIII and SII frames. Notes: 31 x 240 second exposures in Ha + 20x 10 second subs just for the Trapezium (the super bright core of the Orion Nebula--so bright I have to take separate short exposure shots and merge it back in processing). William Optics GT81 APO refractor, ZWO ASI1600MM-Pro mono camera, Astronomik 6nm Ha filter.


Astro Session: July 9, 2018

July 9, 2018 - Reading time: 3 minutes

I recently bought the William Optics FLAT 6A II, and finally made it out under the stars to take some sub-exposures. I paired it with my GT-81 and ZWO ASI071MC color CMOS camera. The FLAT 6A II is a 0.8x reducer/field flattener; it's adjustable for different focal lengths, and so far, with my limited use, it appears to be quite a leap over the old William Optics F6-A I've used for a few years. The ASI071 has an APS-C sized sensor, and anyone with a large sensor astro camera or DSLR knows if you don't want field curvature with your refractor you need some sort of flattener. The FLAT6AII design makes it easy to dial in the correct distance for the scope you're using. The old reducer/flattener worked, but I had to test out a dozen different flattener to sensor distances, and still had to do some cropping and processing to fix the corners. This new FLAT 6AII provides a fairly flat field across the entire view. Equipment: William Optics GT-81 + FLAT 6A II 0.8x reducer f/4.7, ZWO ASI071MC-Cool color CMOS camera - gain 0 offset 8, ZWO ASI120MM-S Guide Cam + 130mm guide scope.

Testing:

With the GT81 and ASI071 I get a 3.54° x 2.35° field of view, and I can capture some big chunks of the night sky. Here are three from the last two nights: [1] the Pelican Nebula (IC 5070) and the edge of the North America Nebula (NGC7000) at the bottom, [2] IC 1396 nebula with the Elephant's Trunk at the top and the Garnet Star bottom left, and [3] M31, our galactic neighbor, the Andromeda Galaxy. 

 

 

Pelican Nebula image info: ZWOASI071MC 39 x 240 second color subs stacked in DSS, processed in PSCC2018

IC 1396 region image info: ZWOASI071MC 21 x 300 second color subs stacked in DSS, processed in PSCC2018

The Andromeda Galaxy. The last time I photographed Andromeda (M31) was 2015, maybe fall of 2014? It's been a while. I was using a DSLR--that was the only camera I had, and I had it on a terribly-used Celestron CG-5 equatorial mount with some aftermarket RA/DEC motors. By "terribly-used" I mean you could drive a truck through the gear backlash. Even so, I still managed to get some decent 30-second exposures of Andromeda, Orion Nebula, and other big bright targets in the sky. Well, I'm back with our galactic neighbor, and with much better gear: 192 x 120-second sub-exposures stacked in DSS, processed in PSCC2018, ZWO ASI071MC camera at -10C, William Optics GT81 APO, iOptron CEM25P EQ mount.