Color Imaging Train: October 21, 2018
Here's my working color imaging train with the William Optics GT81 APO. The leftmost component is the William Optics FLAT 6AII field flattener/reducer which brings the focal length of the GT81 to 382mm at f/4.7. Pretty fast. The problem, of course, with reducers and flatteners is nailing that 55mm T2 distance to the camera sensor. That means the off-axis guider has to be thin (Orion Thin OAG) and the inline filter drawer does as well. The last piece of the puzzle, or bit of trouble you have to deal with is focusing the off-axis guide camera, matching the guide camera sensor distance to the primary camera sensor distance. And I finally had a bit of clear sky at night--bright moon however--to dial this in.
I added the filter drawer to be able to support UHC and other filters with the ZWO ASI071MC color camera. I don't plan on running with a filter most of the time, but some targets call for a bit more contrast.
Posted October 21, 2018
Astro Session: July 9, 2018
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.
Posted July 9, 2018
Astro Session - March 11, 2018
First test shots of M42, the Orion Nebula, M43 De Mairan’s Nebula, Sh2-279 Running Man with the ZWO ASI071MC cooled CMOS camera. No calibration frames, just 17 stacked 300 second light frames, with the sensor cooled to -10C. Last night was not very clear, scattered clouds, fairly poor seeing. I can't wait to test things out with some really clear and dark skies. I definitely need cal frames, because things ended up pretty noisy after processing. I will say, so far, with only a few hours of use, I'm impressed with this ZWO color camera. That doesn't surprise me. ZWO makes a solid camera--I've been using an ASI120MM-S for several years, as my guide camera. It's fast--USB 3, with a small but very sensitive monochrome sensor, and it just always works under any OS on a variety of hardware--Windows, Linux, MacOS. That's what I meant--it shouldn't surprise me that the ASI071MC (quite a bit more expensive and a far more capable camera) just works well. What did surprise me is how much this camera can pick up, bringing out some very faint nebulous areas. I know it has a very wide/high dynamic range. That's one of the things I was looking for in an OSC camera. For this M42 test I used a Gain of 0 and Offset of 8, the minimum recommended by ZWO for long exposure times and HDR (high dynamic range). We'll see how things go on the next clear night. I'd like to test out unity gain settings, and LRN (Lowest read noise) setting, which is high gain, high offset, used for short exposures. (William Optics GT-81 + 0.8x Field Flattener/Reducer f/4.7, ZWO ASI071MC cooled CMOS camera, iOptron CEM25P EQ mount, 30mm mini guide scope with ZWO ASI120MM-S guide cam, INDI/KStars/Ekos observatory control. Location: Stratham, New Hampshire, US. Bortle ~4). Astrobin
