Iris Nebula

[StuartT]

I'm a little underwhelmed by last night's work. This is 4 hours on the Iris Nebula with an Esprit 150, ASI2600MC and L Extreme filter. It took a lot of pulling and pushing to get even this. I guess it's just a very faint target and will need substantially more time. Also, I am not sure I should have used the L Extreme (since this is not an emission nebula). Maybe it's more of a broadband target?

300s subs

Edited September 1, 2022 by StuartT

[wimvb]

This nebula has a very large dynamic range, so you need lots of data, especially if you block part of the light. I’d suggest you skip the L-extreme here.

[StuartT]

36 minutes ago, wimvb said:

This nebula has a very large dynamic range, so you need lots of data, especially if you block part of the light. I’d suggest you skip the L-extreme here.

thanks. Might it even be worth collecting two different exposure times? One for the core and one for the outer parts?

[Elp]

A good image for a short length, you've got a lot of inner detail. I did over 20 hours on this target and didn't get much further than the initial few hours. A lot is to do with processing, esp with something like PI which I don't use, I've seen amazing images of this target with similar duration to yours as a result.

[StuartT]

31 minutes ago, Elp said:

A good image for a short length, you've got a lot of inner detail. I did over 20 hours on this target and didn't get much further than the initial few hours. A lot is to do with processing, esp with something like PI which I don't use, I've seen amazing images of this target with similar duration to yours as a result.

This is worth knowing. I think I will persevere and see what a few more nights can add. BTW - I do everything in PI (calibration, cosmetic correction, integration, post processing). It's a truly amazing piece of software. 

[wimvb]

1 hour ago, StuartT said:

thanks. Might it even be worth collecting two different exposure times? One for the core and one for the outer parts?

If you can get a convincing combination of the data, this can work. But as long as the light pollution isn’t too overwhelming, you can also combine two versions of the same master with different stretch. I’ve done this with good result in an image of the Orion Nebula. However you choose to do it, you need a lot of data to bring out the faint dust.

[StuartT]

27 minutes ago, wimvb said:

If you can get a convincing combination of the data, this can work. But as long as the light pollution isn’t too overwhelming, you can also combine two versions of the same master with different stretch. I’ve done this with good result in an image of the Orion Nebula. However you choose to do it, you need a lot of data to bring out the faint dust.

Good point about two different stretches. I wouldn't have thought of that! I use GenHypStretch in PI which provides a lot of fine control.

My LP isn't too bad. I am Bortle 5 ish

[The Lazy Astronomer]

The Iris is a reflection nebula, so lose the L-extreme for sure - it'll likely be doing more harm than good.

[gorann]

Yes, skip the L-extreme, and you will find that is is actually a very bright nebula and will look good in RGB even after only 4 hours. Will be a perfect catch for your Esprit 150.

CS, Göran

[wimvb]

2 hours ago, StuartT said:

My LP isn't too bad. I am Bortle 5 ish

I also live in a Bortle 5 area (20.5 sky Magnitude), and don’t use any LP filter. But I do need to collect a lot of data to bring out faint nebulosity. Plan to collect at least 10 hrs of data. One other trick you can use is to extract the luminance channel of your colour image, and process that separately. Then combine as LRGB. This can keep the colour mottle under control.

3.5 hrs from Bortle 6-7

https://www.astrobin.com/318629/C/?nc=&nce=
 

A dark nebula from Bortle 5, 15 hrs. The faint stuff you’re after is imo not too different in these two targets.

https://www.astrobin.com/cits92/

Edited September 1, 2022 by wimvb

[StuartT]

On 01/09/2022 at 15:24, wimvb said:

I also live in a Bortle 5 area (20.5 sky Magnitude), and don’t use any LP filter. But I do need to collect a lot of data to bring out faint nebulosity. Plan to collect at least 10 hrs of data. One other trick you can use is to extract the luminance channel of your colour image, and process that separately. Then combine as LRGB. This can keep the colour mottle under control.

Many thanks for this advice. I shall try this

[assouptro]

Tricky target, I haven’t managed to capture an image of this area that I would be happy sharing, I find reflection nebula more of a challenge due to the need to image in rgb instead of narrowband

Well done tweaking that data out of a narrowband filter, you made it difficult for yourself! It’s frustrating when clear moonless nights are rare and you find out you should have taken a different approach, but that’s the thing about this hobby, it’s a mixture of frustration and glee! 
 

Thanks for sharing 

Bryan 

[pipnina]

I'd say you've done very well for the 4 hours of data, given the inclusion of a duo-band filter!

Here's my RGB take on the nebula from the summer twilight-period. This was about 3 hours PER colour! So I had much more time on subject than you did! Using the same camera but a faster telescope (f4 200mm newt)

I reckon that once you try again without the L-extreme you will get very nice images indeed! Being a reflection nebula this is very much a broadband target!

[ncjunk]

Not the easiest target so keep going! It's a great start you have.

I tried imaging this once and was surprised at how awful I managed to make it look - needed a lot more data so I moved onto an easier target🤣

[StuartT]

Thanks everyone. I was thinking of switching out the L Extreme for the L Pro (which lets a lot more through), but the consensus would seem to be for no filter at all.

In which case, have you any tips as to how to process out the inevitable skyglow? (I'm not used to shooting naked!) Presumably it's just a matter of good background extraction in PI? 

Edited September 3, 2022 by StuartT

[Budgie1]

You could try reducing the exposure time and just do more subs, something like 180s or 240s per sub. 

You can use a second pass of DBE if there's still some gradient left and add more points to where the gradient is. Another option is to start off by using GraXpert after stacking, but before PI processing, so most/all gradients are dealt with before you start.

I'm also with the others regarding the filter, defiantly go broadband on this target. The L-eXtreme and L-eNhance kill this type of target.

[The Lazy Astronomer]

1 hour ago, StuartT said:

Presumably it's just a matter of good background extraction in PI? 

Pretty much - use DBE and make sure you give it enough sample points for it to properly model the gradient. Might take a bit of trial and error, but once you get it you should be left with a nice neutral, even background. 

Edit: here's a live example - different gradients in all colours and bad flats in red. Still wasn't quite perfectly flat after DBE, but good enough to work with (nothing but ChannelCombination, DBE and an unlinked STF)

Edited September 3, 2022 by The Lazy Astronomer

[wimvb]

If you're not sure where to set samples in DBE, download a wider view image with the dust well defined, from the internet, and star align that to your image. This is your reference. Then set sample points in the reference image. Save the instance of DBE to the workspace. Then apply to your image.

[Elp]

I tried different methods of background extraction in Siril with my data including excluding areas where the dust would be, still couldn't get the dust from the image even though it's there.

[StuartT]

3 hours ago, wimvb said:

If you're not sure where to set samples in DBE, download a wider view image with the dust well defined, from the internet, and star align that to your image. This is your reference. Then set sample points in the reference image. Save the instance of DBE to the workspace. Then apply to your image.

now this is an excellent idea!