Noisey California Nebula

[Astro Waves]

Finally had a super clear night here in Edinburgh last night. Got to my usual shooting spot, did the standard setup which is getting much more swift including PA and finding target now I gots the ASIAIR Pro (which I'm loving for its simplicity and ease of use). Also received the Optolong L-extreme so thought I would give it a go. I feel like I'm getting there more slowly than I'd like with the imaging results and everything that comes with it etc.......but I'll tell you whats not great, when you forget to turn on your dew heater and also to charge your phone thats running ASIAIR app but regardless I had a nice time. 

The is the first edit I've tried for this image and pretty happy with it I'd say, definitely more on the orange/red side but I like it so stuck with it and sacrificed some whispy detail for a smoother image.

I do have a couple questions, I'm shooting on DSLR and used a pretty low ISO of 800 but I feel the amount of noise I'm getting in the image is pretty darn high as you can see from the results below. I only got about 2 hours integration time but would more time mean a smoother final result? and also the second pic is of the stacked data form Siril I've found since I've started guiding and being able to take longer exposures that I'm getting these consistent lines when shooting, any one know what they are/if there's anything I can do to get rid of them via processing?

Any comments or critiques more than welcome.

 

Edinburgh - Bortle 7 -  Redcat 51, Canon 750D Mod, iOptron Skyguider Pro, ASI120mm Guide, Optolong L-extreme, ASIAIR 

Lights - x46 180 seconds

Darks - x7 180 seconds

Flats - x25 1/40 Seconds

Biases - x25 1/4000 second

[CloudMagnet]

Still a lovely image, taking some more darks would be helpful to reduce that banding. 7 is a bit on the low side, I would aim for around 25 if possible. You also have the disadvantage of an uncooled camera. For the best results, your darks need to be at the same temperature (or as close as possible) to work the best.

I haven't used the skyguider pro, but I would look to introduce dithering into your process as well. It will shift the image around a few pixels between images and have the effect of cancelling out any banding as well, might be worth looking into.

[newbie alert]

Nice image, its called horizontal banding

Edited November 14, 2021 by newbie alert
Adjusted

[Astro Waves]

21 minutes ago, CloudMagnet said:

Still a lovely image, taking some more darks would be helpful to reduce that banding. 7 is a bit on the low side, I would aim for around 25 if possible. You also have the disadvantage of an uncooled camera. For the best results, your darks need to be at the same temperature (or as close as possible) to work the best.

I haven't used the skyguider pro, but I would look to introduce dithering into your process as well. It will shift the image around a few pixels between images and have the effect of cancelling out any banding as well, might be worth looking into.

Ta very much. I know, I know need more darks and I never take enough of them as it usually gets on being too late/being too tired to have the patience to wait for them to tick over even though I should do. I have been looking a cooled camera as this would definitely help so I could do them any time. Had thought about upgrading the mount first to a go-to but now I can plate solve with ASIAIR pretty quickly its really to too bad at all. 

So I do set the ASIAIR to dither every 5 images I think but is it worth it doing it more frequently than that? 

 

20 minutes ago, newbie alert said:

Nice image, its called horizontal banding

Thanks

Edited November 14, 2021 by Astro Waves

[CloudMagnet]

1 minute ago, Astro Waves said:

So I do set the ASIAIR to dither every 5 images I think but is it worth it doing it more frequently than that?

Given you still have that banding, it would be worth doing more dithers. The fewer frames that share the same position as each others means that the chances of banding persisting will drop. It might also be worth increasing the size of the dither to make sure there is visible movement between frames. It might be the case your dithers now just aren't large enough.

[discardedastro]

Random dithering every frame is pretty common. Also worth checking how much you're dithering by in practice, i.e. with widefield you may need to be dithering a fair bit to move the image around a meaningful amount.

I find dark frames are easy to sort - pick a cloudy night when it's cold and just run the camera doing darks all evening. I usually do around 100 120s exposures for darks, which is probably overkill but can't hurt! Alternatively, put it in your fridge if you can't wait and are confident that the optical train/telescope itself isn't introducing any constant light sources. I'd definitely look to do more biases, too, or use a tool like PixInsight's superbias to extrapolate.

Looking good regardless though!

[Astro Waves]

29 minutes ago, CloudMagnet said:

Given you still have that banding, it would be worth doing more dithers. The fewer frames that share the same position as each others means that the chances of banding persisting will drop. It might also be worth increasing the size of the dither to make sure there is visible movement between frames. It might be the case your dithers now just aren't large enough.

Next time I get out there I'll give it a go with making the dithering more frequent and se if that makes a difference. Is banding something that in ingrained in the actual camera or is it something that changes each time you shoot if you get my drift? tried to make a pun out of that but hopefully it makes sense, haha. 

31 minutes ago, discardedastro said:

Random dithering every frame is pretty common. Also worth checking how much you're dithering by in practice, i.e. with widefield you may need to be dithering a fair bit to move the image around a meaningful amount.

I find dark frames are easy to sort - pick a cloudy night when it's cold and just run the camera doing darks all evening. I usually do around 100 120s exposures for darks, which is probably overkill but can't hurt! Alternatively, put it in your fridge if you can't wait and are confident that the optical train/telescope itself isn't introducing any constant light sources. I'd definitely look to do more biases, too, or use a tool like PixInsight's superbias to extrapolate.

Looking good regardless though!

I had a funny image of putting the entire set up my tiny fridge and my partner coming home and opening going "what the heck are you doing?"

I've never really been sure of how many of each darks, flats and biases to take, is it kinda like the more the merrier?

[discardedastro]

Basically banding is in the sensor and is a result of how the camera/sensor reads out pixels/data or inconsistency in the sensitivity of specific pixels in the sensor. Lots of things can cause it, but it is tied to camera/sensor, so calibration helps. Calibration can't magically restore missing data, though - hence why dithering is important, to put those objects on "good" pixels often enough that you actually get data for those regions of the image.

With that much banding you need to at least move 10-20% of your image size over the course of imaging, I'd say. So work out roughly how many subs you're doing and adjust dither movements accordingly!

How many darks/biases/flats you need is best experimentally determined, but yes, more is almost always better. I do 25 flats per filter, 100 frames of bias, 50-100 frames of dark on an ASI183MM-PRO (which is cooled, so that all gets done at -15c)

 

[Astro Waves]

21 minutes ago, discardedastro said:

Basically banding is in the sensor and is a result of how the camera/sensor reads out pixels/data or inconsistency in the sensitivity of specific pixels in the sensor. Lots of things can cause it, but it is tied to camera/sensor, so calibration helps. Calibration can't magically restore missing data, though - hence why dithering is important, to put those objects on "good" pixels often enough that you actually get data for those regions of the image.

With that much banding you need to at least move 10-20% of your image size over the course of imaging, I'd say. So work out roughly how many subs you're doing and adjust dither movements accordingly!

How many darks/biases/flats you need is best experimentally determined, but yes, more is almost always better. I do 25 flats per filter, 100 frames of bias, 50-100 frames of dark on an ASI183MM-PRO (which is cooled, so that all gets done at -15c)

 

nice, thanks for the help, definitely given me lots to think about. 

On a side note I'm looking into CCD cameras and was eyeing up the ASI183-MC and noticed in your sig that you use the MM version, how do you find the amount glow with this camera? I feel like I'm spending for ever trying to read about what cameras to match with the redcat 51 and the 183 seems to be a good fit, don't think I get enough sky time to go down the mono route yet and would probably be easier and more consistent when I know I can frame much easier over multi night shoots using a go-to mount when that time comes. 

[discardedastro]

The 183 might be a pretty good match to the Redcat - I was looking at a Redcat as a potential piggyback option for it if I ever wanted to add a slightly bigger sensor to my DSO scope to widen the FOV!

In terms of calibration and darks - below is the superbias, dark frame, and a single luminance 120s exposure post-calibration, all auto-stretched in PI. The actual intensity of the amp glow isn't huge for shorter exposures - the glow's not very visible on a 120s image in practice, so the calibration sorts it nicely. On longer exposures it's more challenging but I can reliably calibrate out stuff up to about 600s, 900s is a bit iffy sometimes.

At 300s you can see it's a bit trickier to cal out the glow, though with dithering it's manageable. On dimmer targets like Ha it's definitely more of a challenge as the background level is much lower compared to the glow. On brighter stuff like the above it's pretty easy to "outrun" the glow's gain over time. So if you were looking for OSC and relatively bright targets I'd say it's fine. The dark frame below is 900s, which is as bad as it gets - you can also see the corner glow.

Hope that helps!

Edit: And all those Ha frames came together pretty well when integrated, but you do end up with that stacked glow if you can't cal it out - I've done better calibration removal since I processed this though:

Edited November 14, 2021 by discardedastro

[Ceph]

The problem with the bands I know what it is, It is unfortenatelly a build in problem in the sensor on the Canon 750 and 760, those seven lines, if you look carefully, do not go all they way out to the edges.
I owned once a 750 and after I found out the problem I changed down to Canon 700D which do not have them, so you will have this problem as long as you use that camera sorry to say, that means when editing them
away you will alwasy lose some of the object itself. 750 and 760 are not suited for astrophotography.
On mine 750 the lines was most obvious if you split out the blue channel only. Here is how it looked on mine, same thing