Looking for guidance on ASI1600MM Pro exposure times with Narrowband - Forums

Topic starter

Nov 10, 2021 · Edited: Nov 10, 2021

I'm wondering what exposure times people are using with their ASI1600MM cameras please? I have just started using the camera and just started doing narrowband. I had an imaging session for the first time focussed on Ha and with Unity gain and ended up with this:

Crescent Nebula - First attempt at HaRGB
This was with 34x180s narrowband images combined with 48 or so RGB 90s images.

Looking at the Ha stack, the histogram is so far over to the left that it is difficult to stretch properly. I'm assuming that my exposures on Ha are not long enough to really overcome the noise. What would you suggest exposure wise. I'm using an F4.5 908mm reflector FWIW.

Thanks for any suggestions

Andy

Leonidas

Nov 10, 2021

Hi, I'm at f/6 and typically use 600s exposures at unity gain with my ASI1600MM using 6nm narrowband filters. I think 300s would probably be the minimum for me. I'm in a bortle 6ish suburban area. I hope that helps and good luck.

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Andy Wray

Topic starter

Nov 10, 2021

Leonidas:
Hi, I'm at f/6 and typically use 600s exposures at unity gain with my ASI1600MM using 6nm narrowband filters. I think 300s would probably be the minimum for me. I'm in a bortle 6ish suburban area. I hope that helps and good luck.

It does help. I'm in a similar area sky-wise, so would need to do 360 secs based on apertures and filters (I've got 7nm).

Dan_Paris

Nov 15, 2021 · Edited: Nov 15, 2021

For me 300sec at f/4 (Bortle 7 sky). On most objects (like the crescent nebula) it seems enough. I use maximal gain to lower the read noise, I only saturated a nebula once (bubble nebula).

John

Nov 15, 2021

300 sec or 600 sec,depends on your mount. 180 sec is the minimum. gain 139..unity gain. temp -20,iff yoy live in a could area -15 will do it too.

Luca Marinelli

Nov 18, 2021

Andy,

I have imaged with a 10in f4 Newt extensively with the ASI1600 until recently and from Bortle 5+ skies I used 360sec with 3nm filters and unity gain. If you look at my gallery you will be find a number of examples with exposure times for both broadband and narrowband imaging.

Cheers,

–Luca

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Jonathan Piques

Nov 18, 2021

I used a 1000mm f4.5 Newtonian for years and shot 300 second narrowband subs at gain 139, and it worked great. Skies were maybe Bortle 6 - 8. I’ve done 600 seconds and those work well too, but I generally preferred 300.

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Christian Großmann

Nov 20, 2021

Hi Andy,

I used to shoot my narrowband images with exposure times of 300 seconds. I never really got shorter than this. I mainly used my ASI183MM and my 8" f/4 scope. For a while, I had problems stacking the images and applying darks to them. The problem was not related to the exposure time, but I did some experiments. I ended up with usually 600s. I also increased the gain a bit and go over the unity mark. The reason are the fine details in the image. They only get visible if the signal is strong enough to raise above the noise level. For this, you need longer exposure times. The question is, what your expectations are.

The exposure time varies depending on the scope I use. With a wide field of view, I increase the exposure time to 1200s. If the weather is calm and the seeing is properly, I also use 1200s with my 8" f/4 Newtonian. If I am imaging with my big toy (10" f/5), I had to reduce the exposure time to 600s, because the mount is reaching its borders and the guiding is not as calm as on the other scopes.

I did a search for some Narrowband images and looked at the data other members use. I think, that I am in a good spot here. But I have to mention, that Ha is the strongest narrowband signal. If you go for OIII or SII, I can imagine that even 300s is quite low.

Things changed a bit with ma ASI294MM which has larger pixels (only binned to 2x2) than my 183MM (unbinned) and the sensitivity is much better. The 1600MM falls somewhere in between.

I want to encourage you to do some experiments as well. Try some moderatly higher gain settings and/or some longer exposure times. I think it's worth it.

CS

Christian

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David Nozadze

Nov 20, 2021

Hi Adny,

With my ASI294 MM and F3.3 scope, I will do at least 300 secs for the emission nebulae and at least 600 secs for the reflection nebulae, as they tend to be much dimmer. If a bright star is in the shot, it will saturate fast, bleed over to surrounding pixels and, therefore, bloat. But that is an unavoidable sacrifice, I suppose.

If I have a near-perfect seeing, my tracking is sub arc-second accurate, there's no strong wind and clouds, then I may risk going 900 or even longer. But with that, risks of loosing a sub to tracking error, airplane, bright sattellite etc are much higher. So I would only do that only if I have similar conditions over the next two or three nights - i.e. extremely seldom.

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Olly Barrett

Nov 21, 2021 · Edited: Nov 21, 2021

Shot this on my 1600mm Pro 2 days ago with 300 secs exposure, Unity gain (139) and -20C cooling… 300 secs seems optimal to me…
21 Sub-frames.

Steve Argereow

Nov 22, 2021 · Edited: Nov 22, 2021

If I'm shooting with my f4.8 scope I can use 150 second exposures at -15C with 6nm ZWO filters and even less exposure time with the ZWO RGB filters. If I'm using my f7.5 Refractor, 240 seconds is minimum but 300 seconds probably better, I'm currently shooting Abell-85 at 600 sec. The other factor is what you are shooting, if it's a bright object like M31, M8, or M42 you can experiment with shorter times and still get good results. Last month I shot the Soul nebula at 150 sec exposures f4.8 narrowband and I was pleased with the results. I decided to zoom in on the pillars and shot it with the f7.5 scope at 180 sec. I was very disappointed with the results and realized I should have been at 300 sec's with that scope.

There is a great video on Youtube by Dr Robin Glover the S/W developer of SharpCap it's about an hour long but I've watched it several times. He talks about Read Noise, camera temp, LP, exposure times and other topics. Some of his data has the ASI1600, it's well worth a watch for any Astrophotographer at any level.

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Tristan Campbell

Nov 22, 2021 · Edited: Nov 22, 2021

Personally I tend to use shorter exposures, typically 120 seconds or even 60 seconds. Main reason is generally to get more usable subs as if a cloud or haze passes through I lose a minimum of 5 mins rather than 2. Here in UK clear sky time is a very unpredictable and premium resource.

This is 8 hours of 60 second exposures. Typically use gain 200 for narrowband but this also uses gain 0 for bright core of m42.

https://www.astrobin.com/67clrh/

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Douwe79

Nov 22, 2021

Gain at 200, 300 sec exposures, F7, bortle 5 works wel for me.

Abhijit Juvekar

Nov 22, 2021

I found 180 sec at Unity gain is a balanced point for narrowband.
This way you get more frames compared to 300 sec or higher.
Dithering after every 3 frames is more important compared to longer exposures.
More you dither better is your background noise smoothening and hence easy processing the data.

Currently, for LRGB I use 30 sec exposures @ Gain 139
and for Narrowband I use 180 sec exposures @ Gain 139

I tested it with the GSO 6 inch F9 RC tube, Sharpstar 60ED APO refractor and both given good results.

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