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Old 11-12-2021, 09:35 AM
Gastraea (John)
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Question Advice: Noise especially in the red channel

Hi All
I'm not all together happy with my first attempt at Rosette Nebula



https://photos.app.goo.gl/gEz14s38EHZymXCaA

My equipment is Nikon 5300, WO GT-81, Losmandy G11, Optilong L-enhance. Bortle 4 skies.

The image is over 4 hours from 6 min subs and I was expecting more.
There is far more noise in the image than I was expecting especially in the red channel.
Looking at the histograms of the channels coming out of DSS+ (and off the RAW files) the red channel is significantly lower than the green and blue.
I'm guessing this may be due to the DSLR IR filter in combo with the L-enhance???

Anyway there was a screw up with taking the dark images (I know what the temperature was so I'm going to recreate them eventually). So that may be part of the problem but I have some questions with the ISO.
I was shooting ISO400 before I used the L-enhance but I found that 2 min subs had too many black pixels in the red channel (seems to screw up DSS+ somehow). Swapping to ISO800 seemed to fix this but now I'm wondering if that is the wrong choice.

Anyway any advice would be helpful.

Last edited by Gastraea; 11-12-2021 at 10:03 AM.
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Old 11-12-2021, 11:13 AM
Mickoid (Michael)
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John, not knowing much about the Nikon 5300 and it's response to Ha wavelengths, I'm suspecting, despite the long exposures, the camera's stock standard sensor is just not able to get enough signal through the L Enhance filter. These narrow band filters are most effective using a modded DSLR camera where the IR cut filter has been removed. I guess what's happened, in your efforts to emphasise the Red channel in the Rosette nebula, you've stretched the image to the point where it is showing up a lot of noise. Even on modded DSLRs these narrow band filters require a lot more exposure to create a good signal response. Why not check out the camera's native Ha signal response by ditching the L-Enhance filter and shoot the same exposure at say 1600 iso and see what it looks like?
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Old 11-12-2021, 11:49 AM
raymo
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It is very unlikely that 800 was the wrong choice, as the minimum noise sweet spot on most DSLRS lies between 800 and 1600; my Canon 1100D is 1600, and my 600d is 800. From memory I think many budget and mid level Nikons are around the 800 to 1000 mark. The Rosette is far from an ideal target for an unmodded DSLR. You are also using a small scope with limited light gathering power. My 8" Newt brings
out a lot more red than is contained in your image using far shorter subs with my unmodded 600D and no filter.
raymo

Last edited by raymo; 11-12-2021 at 11:54 AM. Reason: more text
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Old 11-12-2021, 12:46 PM
Gastraea (John)
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Thanks guys
I can see an ASI1600 cool or pro in my future.

BTW is there any resource out there that tell you what the emission spectra is for various targets? I seemed to get much better results with the lagoon nebula than Rosette even those it was a much lower exposure time.
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Old 11-12-2021, 01:04 PM
raymo
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I'm not aware of any such resource, but somebody else might be.
The Lagoon is much brighter than the Rosette, as is the Trifid, just down the road from the Lagoon. It is easy to get plenty of Ha [red] to show up in both of them with an unmodded DSLR.
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Old 11-12-2021, 02:19 PM
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Nikolas (Nik)
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Wrong darks as you mentioned and you are using an unmodified and uncooled camera, either way it is still a decent image but it's not the right setup for this target with your unmodified camera
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Old 11-12-2021, 03:22 PM
Startrek (Martin)
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Donít be too disappointed , itís a pretty good image of the Rosette considering your set up
The sweet spot for dynamic range on the Nikon 5300 from what Iíve read is ISO 200 , but you can try ISO400 as well
The Rosette has a brightness of magnitude 9.0 object so very dim target ( compared to the Lagoon at magnitude 6.0 or M42 Orion at magnitude 4.0 )
Your limiting factors in regard to this target -
Sky conditions ?
Moon phase ?
Bortle value for Skyglow ( seems like your in semi dark skies which is good )
Aperture and focal length ( 81mm and 479mm focal length)
Uncooled DSLR camera ( Quantum efficiency of only 40% ) high noise floor even with shorter subs
Uncontrollable temperature for darks
Dim object at mag 9.0

I used a Canon 600D for 3 years and could never get a decent image of the Rosette. Your image, all things considered it quite good so donít be too disappointed
Maybe next time try a brighter target like M42 and experiment with your ISO ( 200 or 400 ) and keep your subs short like 60sec to 90sec but take 2 to 4 hours worth

Ive imaged with the 2600MC for the past 18 months and itís really been a massive improvement from the DSLR days , especially using the L Extreme for OSC narrowband imaging under light polluted skies ( Bortle 7/8 ) and moon phases

The cooled CMOS camera bug will bite you as some stage in the future and you wonít regret it , OSC or Mono

Well done and keep at it

Iíll keep a eye out for your future images

Good luck
Martin
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Old 11-12-2021, 05:18 PM
Gastraea (John)
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Thanks for you kind words all.

I have just ripped the IR filter out of my old D40 so I'll be interested to see if that makes much of a difference. My D5300 is still doing double duty for a general purpose DSLR.

In any case I think I'll get some kind of dedicated astro camera next.
My plans for a C9.25 or C11 can wait.
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Old 13-12-2021, 10:55 AM
Stephane
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Hi John,

Great image of the Rosette. I personally love how you've skilfully made that red pop and kept the sky nice and dark.

I am also having noise issues with my Nikon D7000, but found recently that by calibrating with 30 darks rather than my usual 15, background noise with reduced a little.

Clear skies,
Stťphane
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Old 13-12-2021, 06:27 PM
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rustigsmed (Russell)
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Yes the 5300 has low read noise so you can have a low iso and not worry too much which is good for higher dynamic range.

https://youtu.be/U5d7tuYWnU0?t=333

I think the image is quite fine for a dslr but I know what you mean.
if you want to share your data and calibration frames i/or someone else here could take a quick look at it.

cheers
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Old 14-12-2021, 09:01 AM
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ChrisV (Chris)
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Nice image. But I'm with Mickoid - just about any DSLR has an IR cut filter that will clobber H alpha. You had to really boost the low red signal to bring it out and that shows the noise in your small signal

Either Astro mod or get an Astro camera. I've only ever used these filters with Astro cameras or my canon with the ir filter removed. In the meantime go for some targets with stronger Ha.
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