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Self Critique
One of my best Deep Space photos to date. Still a little noise in the dark areas.
Creative direction
As with any of my Deep Space photos, my goal is to capture the natural beauty of God’s creation.
Specific Feedback
Aesthetic, Conceptual, Emotional & Technical
Technical Details
This is 2 hours of exposure, 12 ten minute exposures at ISO 400 and f/5.6 using my Canon R5 and Sigma 800mmTelephoto lens. I use a Celestron AVX equatorial mount, APT (Astro Photography Tools) to control mount and camera along with PHD2 to assist in the guiding. Processing was done using Siril software and Photoshop.
Description
I am slowly trying to expand my gallery of Deep Space Objects. This is a Nebula known as NGC2237 commonly called the Rosette Nebula. It is one of the larger nebulas in the northern night sky in December.
Critique Template
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Nice capture of this gorgeous object for a “daytime” rig. The R5 captured a good amount of H-alpha red emission and the lens did a decent job with the stars. I actually like that only the strongest areas of Ha came out – an interesting and different look.
The vertical streaks on the right look like “walking rain”. It can have several causes, with a major one being inadequate dark frame correction. I never got rid of it when using DSLRs and camera lenses. I left SO many issues behind and simplified capture and improved processing so much when I went to a modest astro rig with the AsiAIR and PixInsight.
I’ll be going after it again next month – our view to the east is limited by hills and trees. Since I shot it last I have added an autofocuser, which I need with the temperature changes during a normal night.
John, the nebula and star field look good, with some nice details and color in the nebula. I assume you used a 10 min dark exposure for background noise suppression. If so have you tried multiple dark exposures to see how/if the noise changes between exposures? It also looks like the stars are slightly elongated, which suggests something in your system may not have the accuracy to handle the 2 hours of tracking.
John: Amen! I love that the beauty you reference can be found in the stars and the petals of a flower. I’m in awe of some of the telescopic views we get and while Mark and Diane are certainly the experts on this kind of capture and the technical aspects I will comment on the aesthetic and emotional worth which IMO is way up there. Most excellent. >=))>
The slightly elongated stars would be due to tracking errors during each 10-min exposure due to imperfect polar alignment.
“Background” noise will be averaged in the stacking and integration steps when the astro software does its thing with the individual exposures. Two hours total acquisition is pretty good but 12 frames is pretty minimal. It might be better to do 120 1-min exposures. They will need more stretching but that’s what astro software is designed to handle.
With a cooled astro camera, darks are a must for noise suppression in deep sky imagery because the amount of stretching of the histogram for these dim objects will reveal dark current noise that we never have to deal with in daytime photography. And multiple exposures are necessary as the shot noise varies between frames the same as in daytime exposures and needs to be averaged in order to pull out the dark current noise, amp glow and hot pixels. They need to be at the same exposure time and temp as the “lights”. Something like 20 is the recommended minimum – the more the better.
BUT – darks need to be taken with the sensor at the same temp as the lights, and there is no way to control that with regular cameras. You can try, by shooting after the lights if the ambient temp is still about the same. And the lens cap alone isn’t reliable – an additional cover of a velvet cloth is a good idea. There are also issues raised about the validity of darks specifically with Canon cameras, due to the way they handle a dark offset. I’m not up to speed whether this still applies to Canons or is valid for other DSLR and the newer mirrorless cameras.
I would do the darks and run the processing software with and without and see if they help. If the temp is different they will actually add noise.
I actually took six 10 minute darks at the same ISO 400 setting at the end of my lights session which I used during the processing. I realized earlier today that I had the ISO for the biases set to ISO 800 which maybe contributing to the “walking rain” Diane Miller mentioned.
That’s an idea worth checking – biases are not temp-dependent so easy to re-do. I do mine in a very dark inside room with both lens cap and a heavy velvet cloth. I doubt they are critical with the amount of exposure you’re getting in each frame. I’d try with and without. Same for darks.