It’s a lovely clear transparent winter night. Moonrise is at around 20:00. While I still need to take a 6th shot at IC 343 it’s time to move on. I’ve been highly dissatisfied with how grainy my processed images are so tonight I’ll be working with increased gain in the hope that a stronger signal will be easier to work with.
Messier 74 was last imaged exactly 2 years ago and it’s not fit for display:
- M74 annotated.jpg (895.86 KiB) Viewed 729 times
Here we go again. Flats and dark flats are run and I’m imaging by 18:19. Air temp is 33°F
- M74 8x11.jpg (2.21 MiB) Viewed 729 times
36 X 5 min, unbinned, 200 gain, -20C cooling, 1 sec guide rate
Meade 14” LX200GPS @f/6.3 with ZWO ASI2600MC-P camera
The LP filter was mistakenly left out but the moon’s down and contrast is good anyway
This image was processed multiple times as I just kept buggering it in ImagesPlus. Finally just grabbed the SharpCap stacked version I’d saved, stretched it in IP with the lovely ArcSinH function, and did the rest of the processing in PhotoShop. Recently I’d read that the first step in processing an image is to bring the white level about half way to the minimal signal and that works without creating noise. While not a “Roger Quality Level” this is a huge improvement over my last attempt and is suitable for display.
Jill W had contacted me out of the blue, expressing interest in astronomy. That was about 2 weeks ago so I’d invited her by tonight. While M74 was being captured we sat out on the deck with my Nikon 10X50 and chatted while viewing winter’s eye candy. Turns out, Jill and her husband are amateur astronomers and own large telescopes. They’ll try to make ASSNE’s January meeting.
Next up, Mars is at the meridian and brilliant. It’s been moving away for a month or so now and is down to just 13 arc-seconds in size. I’d not done planetary imaging for several months now and there was a lot of trial and error before I was able to best capture it.
Seeing is marginal. The planet’s jumping around and there’s only a faint hint of detail at 21:51 when imaged.
- Mars.jpg (15.07 KiB) Viewed 729 times
14” Meade LX200 GPS at f/6.3 ASI2600MC-P running 1/250 sec at minimal image size of 480X360 pixels.
The moon’s up now but the sky is so dry that working without a filter may not be a limitation. While I’ve used the ASI camera to image the flame/horsehead region wide field with both the Hyperstar and the refractor I’ve not imaged the horsehead itself for years.
Gonna crank up gain to 300. My understanding is that while increased gain reduces dynamic range, it doesn’t impact S/N and does result in a stronger signal that may require less post processing stretching. And stretching is where my images turn to severe pixilation.
IC434
- IC 434 s.jpg (1.14 MiB) Viewed 729 times
22:31 – 00:08 hrs, Jan 9/10 2023
33 X 3 min, unbinned, unfiltered, 300 gain, -20C cooling, 1 sec guide rate
14” Meade LX200GPS at f/6.3 with ASI 2600MC-P camera
First attempts at processing resulted in horrible pixilation. But with minimal processing as done with M74 the image is satisfactory. As with M74, I’ve used the SharpCap stacked image rather than the IP version. Don’t even have a set of 300 gain darks but substituting 200 gain doesn’t seem to matter as we’re working -20°C.
There’s a 12th magnitude quasar showing in Guide 9 but while the camera easily captures adjacent 14th magnitude stars there’s no sign of QSO 1WGA.
In at 00:16. At 28° F the temperature’s not changed much, but I did refocus for each set of images.
Conclusions & lessons learned:
I’ve been over-processing, trying to achieve bright high-contrast images that attract the eye of the general public. Gotta tone it down a bit (literally).
Not sure if my application of higher gain is appropriate. Researching back to a 1/6/2021 forum thread, I see where increasing gain reduces subtle differences in brightness of the object itself but the increased signal strength is beneficial to post processing. With a gain of 300 the dynamic range decreases from 65,535 adu to just 3,300 adu. Which may or may not impact an image lacking subtle transition of brightness. The past couple of times out I’ve been working nebulous objects and have been running gain at 200 and that’s 4,800 adu vs around the 14,000 at my normal setting of 120 gain.
While my biggest problem has been coarse post processing of late, the plan is to run a complete set of dark frames at 300 gain -20C cooling unbinned. The beautiful images posted online all have far greater exposure than my 2 to 3 hours and this might be the best way to clean up my images.
hgp 1/11/2023
