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2600MC and 120 second subs. too long ?

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#1 Spaceman 56

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Posted 19 September 2023 - 03:14 AM

I have been shooting with the 2600MC for a while now at 60 seconds. it is a Colour Camera.

previous to that I was using a DSLR at 30 seconds, which worked pretty good.

 

just as an experiment I thought that I would try 120 second subs, and tonight I am shooting the Tarrantulla Nebula in the Megellian Clouds.

 

the subs are looking very BRIGHT and I wonder if thats Bad ?

 

I shoot without any filters from Bortle 1.  the OTA is F5 and 530mm Takahashi Refractor.

 

any general thoughts about this 120 second subs experiment ?

 

thanks Spaceman


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#2 F.Meiresonne

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Posted 19 September 2023 - 03:48 AM

I shoot 2 to 3 minutes with a comparable astro cam.

 

Is your gain setting to high?


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#3 soojooko

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Posted 19 September 2023 - 03:57 AM

I nearly always shoot 180s subs on my ASI533( F6 60/360mm refractor ). I feel like its right on the edge as far as bloated overexposed stars go. I could probably do with slightly shorter subs. But I have a decent workflow for dealing with the stars. I have experimented with shorter subs, but always found the longer subs got me better data for the same amount of time. eg 100 x 180s subs produce a cleaner stack than 300 x 60s subs.


Edited by soojooko, 19 September 2023 - 05:25 AM.


#4 Spaceman 56

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Posted 19 September 2023 - 04:59 AM

I shoot 2 to 3 minutes with a comparable astro cam.

 

Is your gain setting to high?

I shoot with Gain 100. sorry I forgot to include that.


Edited by Spaceman 56, 19 September 2023 - 05:01 AM.


#5 F.Meiresonne

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Posted 19 September 2023 - 05:54 AM

Then i would try it...stack them and see what you get...

 

I always used 1-3 minutes subs on my DSLR. Recently i took 2 and 3 minutes subs for my Touptek. Seems to work fine in my skies, so i think i will stick to that. 

One big difference might be the skies , i am in B5 you have B1.


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#6 idclimber

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Posted 19 September 2023 - 06:35 AM

With darks skies my threshold is how many pixels are clipped (100-200 pixels). This is a stat that NINA and Voyager give right next to the max ADU. Alternatively I use a PixInsight formula that can give the similar measurements. 


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#7 soojooko

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Posted 19 September 2023 - 07:45 AM

One big difference might be the skies , i am in B5 you have B1.

Oh - I didn't notice that. Well, that changes things somewhat. I've never imaged under B1 skies - I imagine 180s subs might be overkill. I'm in B4 btw.


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#8 FrostByte

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Posted 19 September 2023 - 07:53 AM

I've been shooting 180-second subs at gain 0 in B-3 skies and only saturate a few hundred pixels. I tried the same exposure at gain 100 and found it to be way too bright and saturated a few thousand pixels. I'd say balance it between your threshold for lowest noise versus number of subs. I'll gladly stack fewer subs with marginally more sensor noise, but we all have different priorities.


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#9 Zambiadarkskies

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Posted 19 September 2023 - 08:12 AM

I shoot 300s subs routinely (no filters) under B1 skies.  W

 

I have been shooting with the 2600MC for a while now at 60 seconds. it is a Colour Camera.

previous to that I was using a DSLR at 30 seconds, which worked pretty good.

 

just as an experiment I thought that I would try 120 second subs, and tonight I am shooting the Tarrantulla Nebula in the Megellian Clouds.

 

the subs are looking very BRIGHT and I wonder if thats Bad ?

 

I shoot without any filters from Bortle 1.  the OTA is F5 and 530mm Takahashi Refractor.

 

any general thoughts about this 120 second subs experiment ?

 

thanks Spaceman

 

My thoughts are that you should do some evaluations on the single subs and see how many pixels you are blowing out.  Actually do the experiment.  I would be surprised if you are blowing out much at all.  I routinely shoot 300s subs without filters with a 533 under class 1 skies.  Are you looking at raw subs or autostretches?  Sounds like autostretches to me. 


Edited by Zambiadarkskies, 19 September 2023 - 08:14 AM.

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#10 Spaceman 56

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Posted 19 September 2023 - 10:01 AM

I shoot 300s subs routinely (no filters) under B1 skies.  W

 

 

My thoughts are that you should do some evaluations on the single subs and see how many pixels you are blowing out.  Actually do the experiment.  I would be surprised if you are blowing out much at all.  I routinely shoot 300s subs without filters with a 533 under class 1 skies.  Are you looking at raw subs or autostretches?  Sounds like autostretches to me. 

I am looking at RAW subs. they look very bright. I will post one once the imaging run is done. are your 300 second subs at gain 100 ?

 

Perfect night here. no clouds and no moon. waytogo.gif

 

doing an all nighter and should get about 8 or 9 hours on that Tarrantulla. still no where near your 30 hours. ha ha..   smile.gif


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#11 Spaceman 56

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Posted 19 September 2023 - 10:04 AM

I've been shooting 180-second subs at gain 0 in B-3 skies and only saturate a few hundred pixels.

 

I tried the same exposure at gain 100 and found it to be way too bright and saturated a few thousand pixels. 

I think you may be right Frostbite.

 

I will do what Mr Kennedy said, and see if EKOS can tell how many pixels are clipped.

 

maybe statistics in EKOS can tell me this. 



#12 Oort Cloud

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Posted 19 September 2023 - 10:53 AM

It varies by target; with no bright stars in the field 120s at gain 100 (which I'm pretty sure is what you use) is probably ok. But with some bright stars in the field, you might need to move to 120s/G0, or 60s/G100. Slew over to the HH nebula with Alnitak, or the 7 sisters, and those stars are so bright you might need to drop to 30s/G0 or maybe even 15s/G0 to maintain the star color.
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#13 FrostByte

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Posted 19 September 2023 - 12:01 PM

I think you may be right Frostbite.

 

I will do what Mr Kennedy said, and see if EKOS can tell how many pixels are clipped.

 

maybe statistics in EKOS can tell me this. 

Click the red circle button in the FITS Viewer taskbar and it'll tell you how many pixels are clipped. For this one I had 1475 clipped pixels, which is a bit more than I like, but the kingdom will not be lost. Gain 0.

 

Annotation 2023-09-19 125856.jpg


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#14 BucketDave

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Posted 19 September 2023 - 12:22 PM

If you're looking at clipped pixels, I don't think it matters whether you shoot in Bortle 1 or Bortle 6. It's the stars that are clipping, not the background.

I've just completed a mosaic of the Sadr region and my broadband subs were just 20 secs at gain 100. I was getting a few hundred saturated pixels on my 533MC. That's 0.0025%. If you aim at part of the sky with dimmer stars, you can expose longer before you saturate them.

 

Edit

20 seconds is shooting broadband, to get nice stars. An hour of imaging is enough to get 150+ frames, so plenty of scope to cull those less than perfect.

If shooting narrowband, I've tried from 300 to 900 seconds.  300 was slightly better than 600 or 900 but only by a whisker.  My current modus-operandi is 300" and a dither every frame.


Edited by BucketDave, 19 September 2023 - 01:20 PM.

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#15 Robert7980

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Posted 19 September 2023 - 12:59 PM

I shoot 5 min subs often with no problems. 120 seconds at gain 100 shouldn't be breaking a sweat for it, that's about the minimum exposure I use. For stars I shoot 30 seconds to keep them looking a little nicer and to save time.. Under Bortle 1 you should be able to run 600 sec subs with no major issues, I would but my clear sky time is limited so compromising for a decent number to stack vs exposure time puts me in the 120 to 300 second range... 

 

The only thing gain zero does is waste time and add more noise, I've found it nearly useless... If you're clipping too much at gain 100 just drop the exposure time, there's way more than enough dynamic range at gain 100, it's far more than any screen can hope to reproduce... I've only found a couple targets that gain zero is useful on, Orion and star clusters where you'd like a little more fidelity in the star color and background noise doesn't matter so much. 

 

Here's 10 min unprocessed under B3, its narrowband so not quite the same as OSC, but the results don't vary that much especially on the stars... 

 

get.jpg?insecure

 

Here's 300 seconds under B3 unprocessed single sub with an L filter so higher QE than than the OSC at f/8... Only the cores of the brightest stars are saturated.. 

 

get.jpg?insecure

 

Here's 300 second subs with the OSC unfiltered... Some of the stars are a little blown, but It's not objectionable to me to reach deeper into the faint stuff... 

 

get.jpg?insecure

 

So you shouldn't be having any issues at 120 seconds with a 2600 under B1...  Much of it is how you stretch the image, the 2600's dynamic rage is far beyond what your screen can display...  IMHO most of the investment in the 2600 is to run it at longer exposures, shooting 60 seconds or less isn't using it for what it was designed to do... 


Edited by Robert7980, 19 September 2023 - 01:07 PM.

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#16 Spaceman 56

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Posted 19 September 2023 - 04:00 PM

It varies by target;

 

with no bright stars in the field 120s at gain 100 (which I'm pretty sure is what you use) is probably ok. But with some bright stars in the field, you might need to move to 120s/G0, or 60s/G100. Slew over to the HH nebula with Alnitak, or the 7 sisters, and those stars are so bright you might need to drop to 30s/G0 or maybe even 15s/G0 to maintain the star color.

OK. this makes sense to me. waytogo.gif

 

up to now I have never adjusted the gain for different targets.

 

ISO-400 and 30 seconds for the DSLR, and Gain 100 and 60 seconds for the 2600MC.

 

Frostbites image with the clip Yellow Circle is very useful. I will look at that.

 

Does ASI Studio also tell how many pixels are clipped for images in Fits format ?


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#17 BucketDave

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Posted 19 September 2023 - 04:32 PM

Spaceman56:
ASI Studio doesn't but Tenmon does. Search for it in threads on CN. Written by Nou. That's what I use.

 

I take a 20 second snap at 100 gain and see how many saturated pixels I get.  I then adjust the exposure to get the percentage saturation to about 0.002%.  That's a few hundred pixels on my 533.  You might want to shoot for 0.001% using the larger 2600.


Edited by BucketDave, 19 September 2023 - 04:37 PM.

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#18 PhotonHunter1

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Posted 19 September 2023 - 04:49 PM

I’d suggest using gain 0 - taking advantage of the full pixel well capacity. I use this gain for LRGB and gain 100 for narrowband images. 


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#19 Oort Cloud

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Posted 19 September 2023 - 04:50 PM

OK. this makes sense to me. waytogo.gif

up to now I have never adjusted the gain for different targets.

ISO-400 and 30 seconds for the DSLR, and Gain 100 and 60 seconds for the 2600MC.

Frostbites image with the clip Yellow Circle is very useful. I will look at that.

Does ASI Studio also tell how many pixels are clipped for images in Fits format ?


I would say adjust exposure first. If that's not enough, then drop the gain.

I usually use gain 0, but that's because I prefer fewer, longer subs, and my mount can usually track/guide acceptably for however long I need it to.
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#20 limeyx

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Posted 19 September 2023 - 08:59 PM

I have been shooting with the 2600MC for a while now at 60 seconds. it is a Colour Camera.

previous to that I was using a DSLR at 30 seconds, which worked pretty good.

 

just as an experiment I thought that I would try 120 second subs, and tonight I am shooting the Tarrantulla Nebula in the Megellian Clouds.

 

the subs are looking very BRIGHT and I wonder if thats Bad ?

 

I shoot without any filters from Bortle 1.  the OTA is F5 and 530mm Takahashi Refractor.

 

any general thoughts about this 120 second subs experiment ?

 

thanks Spaceman

First, as Freddy said check you have reasonable gain / offset configured

 

Then what I do is (using NINA) take a test shot. In the image statistics it tells you the minimum pixel value and maximum and in ()s, how many pixels are at that value

 

The max value for my sensor in NINA shows as I think 65532 so any pixel at that high level is "clipped" i.e. probably higher than that but the data was truncated. I try to keep that value <1000 pixels

 

Same for the minimum. Pixels down there are likely lost in the noise floor, so you want that count low too

 

Adjust the exposure until you minimize both numbers. If you use filters, you will likely have a different exposure length (and same if you go to darker skies etc)

 

Obviously you need to keep the exposure time within what your mount will guide to as well if the mount has limits


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#21 limeyx

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Posted 19 September 2023 - 09:00 PM

I've been shooting 180-second subs at gain 0 in B-3 skies and only saturate a few hundred pixels. I tried the same exposure at gain 100 and found it to be way too bright and saturated a few thousand pixels. I'd say balance it between your threshold for lowest noise versus number of subs. I'll gladly stack fewer subs with marginally more sensor noise, but we all have different priorities.

I may need to move to gain 0 for narrowband too. At 100 I think I am saturating too many even at 60 seconds (Bortle 6/7)


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#22 unimatrix0

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Posted 19 September 2023 - 09:43 PM

I'm not sure what you guys seeing being over saturated. I can shoot 30 seconds no problem at gain 100 with the 533mm with an F3 scope  L-R-G-B. For the R/G/B sometimes I'm thinking 60 seconds would be better off.  Surely 60 seconds (at gain100)  with a f5.6, again no problem.  And that's the mono. At Bortle5. 

My 5 minute sub at gain100 with a 3nm narrowband filter is barely cuts above the noise level.  I should be shooting 7 or 10 minute subs really.  

 

Are you guys checking the unstretched sub, how many stars peaking through?  I usually only have just a couple, the brightest one.  

 

Also- it's really target dependent, Shooting with blue giants, surely it will over saturate at even at 5 seconds, there is no cure for that.    Pleiades-  Maybe that's the only one I would go gain 0 really. Other stuff, no.  With narrowband? 

 

Well, if I want to stack noise only, maybe then I would set gain 0. 


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#23 Drothgeb

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Posted 19 September 2023 - 09:48 PM

OK. this makes sense to me. waytogo.gif

 

up to now I have never adjusted the gain for different targets.

 

ISO-400 and 30 seconds for the DSLR, and Gain 100 and 60 seconds for the 2600MC.

 

Frostbites image with the clip Yellow Circle is very useful. I will look at that.

 

Does ASI Studio also tell how many pixels are clipped for images in Fits format ?

Both Siril and Affinity will show how many saturated pixels you have. I prefer Siril, it even shows which stars are saturated. I think you were using it to check for tilt, star saturation is in the same menu.


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#24 soojooko

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Posted 20 September 2023 - 03:22 AM

Both Siril and Affinity will show how many saturated pixels you have. I prefer Siril, it even shows which stars are saturated. I think you were using it to check for tilt, star saturation is in the same menu.

I use Affinity Photo - but have no idea how to do this. If you could explain, I would really appreciate it. Thanks.


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#25 Spaceman 56

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Posted 20 September 2023 - 04:45 AM

IMHO most of the investment in the 2600 is to run it at longer exposures, shooting 60 seconds or less isn't using it for what it was designed to do... 

hmmmm.....

 

can you explain this further Robert ?




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