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LRGB Imaging in Bortle 9

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#1 Snakey93

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Posted 18 May 2022 - 09:01 PM

Just came off an ASI183MC Pro OSC and finally got my 1st mono cam an ASI294MM Pro.

 

I took some test shot at M3 with an L filter yesterday at 120s (bin2) and found that while it captured quite a lot of start, the image look kinda over exposed (not sure if this is really the right term to use) and also captured a lot of LP.

This is essentially the same exposure setting I was using on my OSC. Only difference was I was using an Opteron L-Pro Broadband Filter (Bin1).

 

Couple of questions here:

 

1. Should I be dialing back my exposure and just capture more subs? Or should I just continue with 120s and process out the gradients?

2. With the 294MM Pro I can choose between Bin 1 or Bin 2. When I take my calibration frames do I also need to take them in Bin 1 and Bin 2? Or does it not matter?

3. I understand there is a 4:1:1:1 ratio for LRGB imaging. Can I assume that the ratios refer to the number of subs and not exposure? Eg. for every 1 R,G or B sub, I need to capture 4 L sub.

 

Would greatly appreciate any other tips & tricks or information which you think would be useful for a newbie like myself. Thanks in advance for the guidance.


Edited by Snakey93, 18 May 2022 - 09:02 PM.


#2 dx_ron

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Posted 18 May 2022 - 11:44 PM

1. It makes a lot less difference than you might think. Total integration time is the key.

2. Calibration frames must match the light frames

3. 4:1:1:1:1 is just a rule of thumb. It refers to total exposure time


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#3 m3guy

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Posted 18 May 2022 - 11:46 PM

I'm not sure about your binning question.  But for me, shooting at bortle 7, I've had better results shooting 60sec subs or faster at 120 gain with my 294mm.    As for ratio -  I usually shoot 3 frames Lum for each RGB set but it's a loose guidethat I'll adjust depending on target.     SharpCap has a sub exposure calculator that I've found really helpful for giving me a ballpark exposure setting.   If you're in a white zone even 60 seconds may be long,  Run a couple of tests with the same amount of integration time and different sub exposure settings and see what you get..



#4 OldManSky

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Posted 19 May 2022 - 07:42 AM

Calibration frames (darks, flats, bias, dark-flats) must match the light frames in all settings.  That includes binning.

 

Without the little RGB filters on the pixel array, and without the L-Pro filter in front of those, you're getting a lot more light to the mono chip, making your shots look "over exposed."  They're likely NOT actually over-exposed, they're just lighter than you're used to.  As long as the stars aren't saturated to the point of clipping, they're probably fine.  You'll just have to process them a bit differently.

 

As dx_ron pointed out, that 4:1:1:1 ratio is a rule of thumb, a starting point.  Not an actual rule.  You'll need to do some experimenting to see what's best for your equipment and location(s).  But it does refer to total integration time, not number of subs or exposure time for each individual sub.

 

Enjoy the new camera!


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#5 AstroPharma

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Posted 19 May 2022 - 10:06 AM

I did some broadband shooting on my Bortle 9 roof a few times. It is so frustrating that I decided against it all together. BUT, if you do have the patience and hard drive space you can actually get decent images. Try using a LP filter like the L-pro and limit your exposure time to 60s. You really need atleast 20 hours of total integration to get any kind of good data at Bortle 9. 

 

Goodluck 


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#6 gcardona

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Posted 19 May 2022 - 10:47 AM

As others have mentioned, exposure time is the key See my Astrobin, all of my recent captures have been from Bortle 8-9, and all are 15 hours or so.


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#7 Snakey93

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Posted 20 May 2022 - 04:17 AM

Thanks for chiming in guys. Appreciate all the advise. Looks like there's still gonna be a fair amount of experimenting



#8 klaussius

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Posted 20 May 2022 - 08:01 AM

I did some broadband shooting on my Bortle 9 roof a few times. It is so frustrating that I decided against it all together. BUT, if you do have the patience and hard drive space you can actually get decent images. Try using a LP filter like the L-pro and limit your exposure time to 60s. You really need atleast 20 hours of total integration to get any kind of good data at Bortle 9.

Goodluck

This.

120s would overexpose (as in clip stars) with my setup and skies. Yours doesn't seem very different so I'd suggest lowering exposure to 60s. On very bright clusters I even do 30s at times.

Then again my camera is 12bit and yours is 14bit, so ymmv.

Using that L pro as luminance may help or it may not. It depends a lot on the target. In my experience it mostly helps, but don't expect a dramatic improvement.

Images with it will be darker and you can expose subs for a little longer, but total integration time is still what matters the most.

Edited by klaussius, 20 May 2022 - 08:04 AM.

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#9 TareqPhoto

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Posted 20 May 2022 - 09:38 AM

Isn't the exposure value also depend on the scope being used? For example i once was able to go up to 200-300sec with RGB filters and mono using my Newt 8" F/5 native, also about 120sec just fine with my ST80, i can't remember if i did also 240 with LRGB using my new 90mm triplet, on some parts of the sky i saw that LRGB with 240s less brightness or LP or gradient than another frame with 60-120s, so i can't just say i will always use the color camera or LRGB at lowest exposure from my area, i live under Bortle 8, and maybe it became Bortle 9 after they installed LED streetlights but i didn't do imaging since a while ago.



#10 unimatrix0

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Posted 20 May 2022 - 10:26 AM

With my limited knowledge, but seeing a lot of posts of the 294MM pro in the past-   120 seconds on broadband- at Bortle 9-  with a mono 294 sounds too much to me. 

 

You didn't mention what telescope you're using. 

 

I mean, it's a big difference between imaging  with F5.6 refractor vs a  Celestron Cass at F11,   but either way 120seconds in B9 skies and mono still sounds too much for either of them.  Just my 2 cents. 


Edited by unimatrix0, 20 May 2022 - 10:29 AM.


#11 TareqPhoto

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Posted 20 May 2022 - 12:45 PM

With my limited knowledge, but seeing a lot of posts of the 294MM pro in the past-   120 seconds on broadband- at Bortle 9-  with a mono 294 sounds too much to me. 

 

You didn't mention what telescope you're using. 

 

I mean, it's a big difference between imaging  with F5.6 refractor vs a  Celestron Cass at F11,   but either way 120seconds in B9 skies and mono still sounds too much for either of them.  Just my 2 cents. 

That is right, so for example, from your signature, your have GSO RC6 which is F9, do you shoot at F9? If yes then what is your exposure for broadband in Bortle 9? And if you reduce it to like F6-F7, then what will be your exposure for LRGB or even a color camera?



#12 Snakey93

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Posted 20 May 2022 - 10:04 PM

With my limited knowledge, but seeing a lot of posts of the 294MM pro in the past-   120 seconds on broadband- at Bortle 9-  with a mono 294 sounds too much to me. 

 

You didn't mention what telescope you're using. 

 

I mean, it's a big difference between imaging  with F5.6 refractor vs a  Celestron Cass at F11,   but either way 120seconds in B9 skies and mono still sounds too much for either of them.  Just my 2 cents. 

I'm shooting with a Redcat 71@F4.9. In the past with my ASI183 OSC was doing 120 to 180s with a L-Pro filter. Now with the mono I've not tried  the L-pro. I'm using the Optolong LRGB filter set.

So I guess it makes sense, the mono cams should be more sensitive and the L filter should be letting in more light (LP included) so I probably have to cut my exposure time. Is there an avg ADU i should be aiming for?



#13 Sheridan

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Posted 21 May 2022 - 06:17 AM

What's my dslr'S 120s is washed out without filters on my 80mm F6. The best I can get is roughly 30 to 45 seconds bortle 9.

#14 AstroVagabond

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Posted 21 May 2022 - 10:00 AM

Not a direct answer but as a second year beginner with a ASI533MC Pro and ASI294MM Pro I've started to use the Optimal Exposure Calculator plugin in N.I.N.A. to provide guidance on exposure length.

 

For example if I use my ASI533 with a luminance filter under my Bortle 7-8 skies the recommended exposure is 15.36 seconds. Same configuration under Bortle 3-4 skies gives me a recommended exposure of 368 seconds.

 

I don't have enough data points yet to draw any conclusions. I'll use the same configuration under Bortle 1 skies end of June and collect additional data. Skyglow is a component of the process Optimal Exposure Calculator uses so I'm not surprised by the recommendations based upon how dark the skies are as I change imaging locations.

 

Last year I saw the two videos by Dr. Robin Glover. They got me thinking that my beginner view that the goal to achieve the longest possible exposure might be flawed. So in year two I'm taking a different approach by using the Optimal Exposure Calculator plugin. I'll also give Sharpcap Smart Histogram a try to see if it corelates with what the Optimal Exposure Calculator is recommending.

 

I have the compute power and storage to handle short exposures if that is what is best so shorter exposures are a non-issue from that perspective. And what makes this hobby fun for me is trying things on my own, self discovery, to establish my personal preferences. 


Edited by AstroVagabond, 21 May 2022 - 10:02 AM.

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#15 gsaramet

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Posted 22 May 2022 - 04:10 AM

So, a bit of news, mostly for other beginners who might have similar issues smile.gif

 

Mount arrived - great. It seems to work great. Scope arrived. Not the smallish refractor which would have been my first choice, but 200/800 newt, second hand, available on spot smile.gif

 

So far, only trouble is weight. Instead of grabbing the mount and taking it outside with all things on, I have to travel a bit: first mount and legs, than scope, than weights. 

I still need a collimator and a coma corrector. 

 

What happened and made me post this is that I run into the OPPOSITE problem. Before I was limited to 1.5 secs of exposure. Now I discovered first hand that you CAN expose too much. So, thanks for the book recommendation, most useful! 

 

I won't post this into first image category but... here it goes. 10x5 minutes subs, dslr, M101, pretty bad processing

 

pinwheelcn.jpg


Edited by gsaramet, 22 May 2022 - 04:11 AM.



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