IC 1848 in Ha
Posted: Sun Sep 30, 2018 10:20 pm
Ordinarily I like to wait for all the pieces to come together on a finished product but in this case I was so thrilled with this preliminary image that I wanted to share it. This is a portion of the Soul Nebula.
Note that the technical details (see below) gives a break down by temperature. For this image, however, I lumped them all together. I really would like a minimum of 50 darks per temperature bucket. That will take some time. When ready I will re-post with an updated image.
One thing that stands out is the 200-second exposure that I used. Initially I tried a "normal" exposure of 50 seconds which I use for LRGB. That led to disappointing results. The signal was so embedded in noise that only the brightest parts were visible in a stretched frame. In my opinion no amount of stacking could save it.
I turned to the internet and discovered an "ideal exposure" calculator at Starizona. Most of the cameras in the dropdown were CCD but they did add several ZWO CMOS cameras. I downloaded the code. I found a bug in the implementation of ZWO cameras. They were not taking into account that these are 12-bit and 14-bit cameras, unlike CCDs which are 16 bits. I ran through the procedure they described for finding the ideal exposure for my Ha filter and Altair 290 at unity gain. It converged at 200 seconds.
Note that 200 seconds is at the "highest noise" setting of the calculator. I did not run through the steps for "moderate noise" and "low noise" because I knew that this meant even longer exposures, and since I do not have active guiding I was concerned about star drift. Thankfully, my mount was up to the task, and can probably go longer.
In a future post I want to do a comparison of the calculator with the Brain.
By the way, here is Sara Wager's image of IC 1848 that I aspire to.
Technical Details:
William Optics 71mm f/5.9
Altair 290M camera (uncooled)
Orion 6nm Hydrogen Alpha filter
Unitron Model 142 GEM
Passive tracking with PEC
No active guiding
Gain 389 (1.0 e-/ADU, FWD: 4ke-, Read Noise: 1.38e-)
Offset: 30 ADU
Exposure: 200s
Camera rotation: 355 deg E of N
Ha:
48.0 degF: 8 frames
48.5 degF: 21 frames
49.0 degF: 11 frames
49.5 degF: 1 frames
Darks:
48.0 degF: 20 frames
48.5 degF: 21 frames
49.0 degF: 32 frames
49.5 degF: 29 frames
Flats: 50
Bias: 100
Temperature-matching disabled until I have more darks per temperature bucket.
Total integration time: 136 minutes
75% waning gibbous Moon high in the sky.
SharpCap 3.1.5219
PIPP 2.5.9
Deep Sky Stacker 3.3.2
StarTools 1.3.5.289
Note that the technical details (see below) gives a break down by temperature. For this image, however, I lumped them all together. I really would like a minimum of 50 darks per temperature bucket. That will take some time. When ready I will re-post with an updated image.
One thing that stands out is the 200-second exposure that I used. Initially I tried a "normal" exposure of 50 seconds which I use for LRGB. That led to disappointing results. The signal was so embedded in noise that only the brightest parts were visible in a stretched frame. In my opinion no amount of stacking could save it.
I turned to the internet and discovered an "ideal exposure" calculator at Starizona. Most of the cameras in the dropdown were CCD but they did add several ZWO CMOS cameras. I downloaded the code. I found a bug in the implementation of ZWO cameras. They were not taking into account that these are 12-bit and 14-bit cameras, unlike CCDs which are 16 bits. I ran through the procedure they described for finding the ideal exposure for my Ha filter and Altair 290 at unity gain. It converged at 200 seconds.
Note that 200 seconds is at the "highest noise" setting of the calculator. I did not run through the steps for "moderate noise" and "low noise" because I knew that this meant even longer exposures, and since I do not have active guiding I was concerned about star drift. Thankfully, my mount was up to the task, and can probably go longer.
In a future post I want to do a comparison of the calculator with the Brain.
By the way, here is Sara Wager's image of IC 1848 that I aspire to.
Technical Details:
William Optics 71mm f/5.9
Altair 290M camera (uncooled)
Orion 6nm Hydrogen Alpha filter
Unitron Model 142 GEM
Passive tracking with PEC
No active guiding
Gain 389 (1.0 e-/ADU, FWD: 4ke-, Read Noise: 1.38e-)
Offset: 30 ADU
Exposure: 200s
Camera rotation: 355 deg E of N
Ha:
48.0 degF: 8 frames
48.5 degF: 21 frames
49.0 degF: 11 frames
49.5 degF: 1 frames
Darks:
48.0 degF: 20 frames
48.5 degF: 21 frames
49.0 degF: 32 frames
49.5 degF: 29 frames
Flats: 50
Bias: 100
Temperature-matching disabled until I have more darks per temperature bucket.
Total integration time: 136 minutes
75% waning gibbous Moon high in the sky.
SharpCap 3.1.5219
PIPP 2.5.9
Deep Sky Stacker 3.3.2
StarTools 1.3.5.289