Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

  • Announcements

    sgl_imaging_challenge_banner_lunar.thumb.jpg.ef4882eb5fb3610f8a68e5e6913de0e3.jpg

groberts

ZWO1600MM-Cool & LRGB Imaging Settings

Recommended Posts

groberts    85

Transitioning from DSLR, I've had the ZWO for a few months now and for the first time been having a lot of fun with narrownband.  In general what with summer and the sky I've been short of suitable LRGB targets but now the nights are getting darker and the sky's changing things are improving. I've particularly been looking forwards to M31, which in the past has come out well with my DSLR and is, of course, just a beautiful object.

So the other night I shot 60sec exposures at Gain 300, Offset 10 @ -20C, 40xL + 20xR + 20xG + 20xB subs + full calibration.  The initial outcome after a bit if stretching + compiling is disappointing and I'm wondering what others have found successful with this type of target with this camera.  It seems obvious to me that either 60 secs is too long and / or the gain is too high?  I've already learned that this is a very sensitive camera but having successfully used similar settings + longer exposures (180 sec) for Ha-type objects and narrowband, thought that something similar at 60 secs would be at least ballpark OK and am surprised by the outcome - oh well.

Thanks, Graham

             

M31 RGB (Small).jpg

Share this post


Link to post
Share on other sites
kens    147

Offset 10 is too low at gain 300 - 50 is the default at that gain or you risk underclipping (if thats the right term). Also at gain 300 you have the lowest dynamic range.Try the unity gain setting (139/21 gain/offset) or around 70/14.

You'll need to experiment with exposures as it depend on your sky background. But with the low read noise you don't need much to swamp the read noise. e.g at 300 gain the peak wil be somewhere around 1300 to 3000 ADU (depending on which school of thought you follow i.e. 3xRN squared or 20xRN). At gain 70 you want the peak around 300 to 600 or so. Note that these are much lower than the usual 1/4 to 1/3 scale recommended for DSLR.

It sounds like you have quite a bit of LP (judging from the LP filters in your sig) so that will have an impact on LRGB vs narrow band. You may need much shorter exposures but take lots of them to get the required integration time.

Edited by kens

Share this post


Link to post
Share on other sites
groberts    85

Thanks Ken, to be honest I haven't got my head around Gain-Offset-ADU yet so perhaps this was inevitable!

I mostly used a modded DSLR + Astronomik CLS filter before - are you saying that as a result it was taking out light that the mono LRGB therefore sees and, as a result, the equivalent light reaching the sensor is itself greater by comparison - which makes sense?

I still can't get a handle on the very short exposures with the ZWO1600.  Oh well, some more experimentation I guess - Rome wasn't built in a day!

Edited by groberts

Share this post


Link to post
Share on other sites
kens    147

Whilst that is true, what I meant was that when you have  light pollution the sky background is much brighter than a dark sky. So you risk saturation and loss of dynamic range if you expose too long. When you image in light pollution the signal is the sum of the target and the light pollution. So what you need to do is expose the sky background sufficiently to overcome the read noise but not much more. That way your faintest targets are above the read noise. As a result the exposure time will be much less than in a dark sky. A DSLR with much higher read noise needs longer exposures to overcome the read noise. Now with LP you have a lot more noise  (unwanted sky signal) so also you need longer integration times to get equivalent image quality to a dark sky. In fact there is a practical limit on just how much quality you can get with light pollution. Short subs and long integration equals lots and lots of subs. 

So in a nutshell: with a DSLR you were probably told to expose so that the histogram peak (the sky background) was about 1/4 of the way off from the left side which corresponds to about 16000 ADU. With the ASI1600 that is way too much. At a gain of 70  is should be around 600 ADU which is just 1% of full scale. Just be sure there is a clear gap on the left of the curve

Share this post


Link to post
Share on other sites
groberts    85

Many thanks Ken that's very helpful.

Any thoughts on exposure time at suggested settings for M31, or with lower gain is 60 secs likely to be OK?  Of course in the end experimentation will answer the question but just thought you might already have a gut feel from experience with this camera - it sure is very different to a DSLR in so many ways but then again it's so much more powerful.    

Regards, Graham

Share this post


Link to post
Share on other sites
wimvb    1,973

From what I've seen on the internet (having just bought a zwo camera myself), you can either go with high gain+offset and short exposure times, or with 0 gain (10 offset) and long guided exposures, 300 to 600 seconds. I've seen very impressive results with the latter. Total time on target doesn't vary much though. This means either lots of short or fewer long exposures. With the file size of the asi1600, I'd personally prefer fewer exposures.

Edited by wimvb

Share this post


Link to post
Share on other sites
kens    147
10 hours ago, groberts said:

Many thanks Ken that's very helpful.

Any thoughts on exposure time at suggested settings for M31, or with lower gain is 60 secs likely to be OK?  Of course in the end experimentation will answer the question but just thought you might already have a gut feel from experience with this camera - it sure is very different to a DSLR in so many ways but then again it's so much more powerful.    

Regards, Graham

The exposure time is not really related to the target but to the background. The integration time would vary depending on the target - the fainter the target the more integration time you need. Im using 30 second exposures at gain 70 in luminance and 30 seconds at gain 139  for RGB using the RC8 at f/8. The sky here is Bortle 5, orange zone. There are so many variables you need to experiment. I'd suggest to set your gain to 70 with offset 14. Start at, say, 30 seconds and check the histogram. If the peak is around 600 you are around the right spot. If below that then increase the exposure in proportion. If higher you probably want to reduce gain rather than go shorter.  If so, drop the gain to zero with offset 10. I don't have my lookup chart to hand but at that gain you want the peak to be more like 100 to 200. 

I'll typically take 120 subs of L and 40 or 50 in each of RGB. That's equivalent to around 2 hours total integration. But I generally think I'm underdone when I review the results on fainter targets. Hope this helps you

 

Share this post


Link to post
Share on other sites
kens    147

Just checked my cheat sheet and at gain 0  you want the histogram peak around 400-500 ADU

Share this post


Link to post
Share on other sites

Sounds like I may have been lucky with my M31, I used gain 300 and didn't think to check the offset. This worked fine with 30 second exposures at f4.7, but this was from a dark site.

Share this post


Link to post
Share on other sites
Rico    79

@groberts how are you getting on with the 1600m? I'm hoping to move from a dslr at some point as well and im in a bortle 5 zone too.

Share this post


Link to post
Share on other sites
groberts    85

In short - very well.  You can see some of my images and issues in my blog here:

https://watchthisspaceman.wordpress.com/

I have found the transition from DSLR to the ZWO1600 more tricky than anticipated but it's been a very rewarding journey and IMO my imaging has greatly benefited from the change.  As you'll see I got the camera + x8 EFW package and have been very pleased with this package.  Narrowband especially has been a lot of fun, just revisiting previous DSO targets has yielded some eye-opening results - broadband remains work-in-progress.

I had previously thought that the next step would be a larger scope but I am very pleased that for the moment I took this route instead.  I was a little put off by the added complexity but the reward is in the results.  Also with the limited imaging time we get in the UK with cloud etc the high sensitivity and shorter exposures than required with a CCD is a real boon.

If you want to know any more or have any queries just contact me directly.  If you're really going to take the plunge, my advice is do it sooner than later in order to take advantage of the winter DSO objects that are now appearing over the eastern horizon.

Graham

             

 

Edited by groberts
  • Like 1

Share this post


Link to post
Share on other sites
Rico    79

Thanks Graham. I'm certain that I will make the transition as some point and my impulsive side is one click away from making the order. However, I'm no different to the many who find the move to a mono camera quite daunting.

Thanks for the link ... I'll let you know how I get on.

Share this post


Link to post
Share on other sites
Astrith    135
On 10/22/2017 at 17:29, groberts said:

In short - very well.  You can see some of my images and issues in my blog here:

https://watchthisspaceman.wordpress.com/

I have found the transition from DSLR to the ZWO1600 more tricky than anticipated but it's been a very rewarding journey and IMO my imaging has greatly benefited from the change.  As you'll see I got the camera + x8 EFW package and have been very pleased with this package.  Narrowband especially has been a lot of fun, just revisiting previous DSO targets has yielded some eye-opening results - broadband remains work-in-progress.

I had previously thought that the next step would be a larger scope but I am very pleased that for the moment I took this route instead.  I was a little put off by the added complexity but the reward is in the results.  Also with the limited imaging time we get in the UK with cloud etc the high sensitivity and shorter exposures than required with a CCD is a real boon.

If you want to know any more or have any queries just contact me directly.  If you're really going to take the plunge, my advice is do it sooner than later in order to take advantage of the winter DSO objects that are now appearing over the eastern horizon.

Graham

             

 

An interesting site . Good reference look up for the ASI 1600 Mono Cool.

Share this post


Link to post
Share on other sites
brrttpaul    1,177

Hi guys when you say check the histogram for the ADU what exactly am I looking at? I see the histogram in sgpro and when I hover the mouse over the star the figures jump and it has mean average median maximum etc, which is the most important one I should be looking at?

Share this post


Link to post
Share on other sites
spillage    302

I have been using APT which has pixel aid for my ADU levels, it also has a handy flats program. Although I seem to find Unity setting gives me the best results so far. We could really do with a few clear night in a row to run some decent experimental shots.

I am totally impressed with the few images I have taken compared to my dslr.

Spill.

Share this post


Link to post
Share on other sites
brrttpaul    1,177

I literally spent hours last night before turning in trying out different settings trying to get my head around it , heres what puzzles me, high gain and offset short exposures, 0 gain 10 offset long exposures 300 to 600, peak ADU around 600. so I tried a few random shots 0 gain offset 10 and I look at the stats and lets say its showing 600 for arguments sake, Am I suppossed to try and get that down to 400 for optimal exposure? because if so we are talking just a few seconds so how is that for long exposures? whereas gain 300 offset 50 the ADU is 2650. Am I looking at this all wrong?

Share this post


Link to post
Share on other sites
kens    147
On 12/11/2017 at 22:00, brrttpaul said:

Hi guys when you say check the histogram for the ADU what exactly am I looking at? I see the histogram in sgpro and when I hover the mouse over the star the figures jump and it has mean average median maximum etc, which is the most important one I should be looking at?

Mean or median are what you normally lok at. They should be much the same and represent where the histogram peaks.

1 hour ago, brrttpaul said:

I literally spent hours last night before turning in trying out different settings trying to get my head around it , heres what puzzles me, high gain and offset short exposures, 0 gain 10 offset long exposures 300 to 600, peak ADU around 600. so I tried a few random shots 0 gain offset 10 and I look at the stats and lets say its showing 600 for arguments sake, Am I suppossed to try and get that down to 400 for optimal exposure? because if so we are talking just a few seconds so how is that for long exposures? whereas gain 300 offset 50 the ADU is 2650. Am I looking at this all wrong?

The ASI1600 has a 12bit ADC so all values are multiplied by 16 (2 to the power 4) to give a 16bit value. 

I've started using a fixed offset of 50 as it seems that ZWO is going to fix it in its drivers so may as well follow suit.

Now there is no universal optimal exposure - its always a balancing act. What you want is  to expose enough for the peak value  (histogram mean or median) to be far enough above the read noise that it is not a problem. That varies with gain and somewhere between 3x and 10x read noise squared are the sort of numbers bandied about. And it also depends on the sky background. A light polluted sky might reach that value in 30 seconds, a dark sky could take several minutes. So your minimum exposure aims to get to that point. The upper limit is set by how many stars are saturated and is personal choice. Longer exposures means more saturated stars as does higher gain for a given exposure.

Its possible you are looking at this wrong. Many people seem to think that long exposures are a must. To me the exposure time is a means to an end. What is really important is integration time - the total time spent on target. Back in the days of film we would expose a single shot for hours if possible - the limitations were film sensitivity versus reciprocity failure. Then CCD came along and stacking many subs of several minutes became possible. Shorter subs are a huge benefit. Nothing worse than taking a two hour exposure on film and only finding out it was ruined days later. But those CCDs needed lots of disk space (300Mb used to be a BIG hard drive). Now we have low noise CMOS and even shorter subs are possible. But you then take even more subs and take up even more disk space in MB but as percent of hard drive its no different and in terms of processing time it is also no different.

 

Share this post


Link to post
Share on other sites
brrttpaul    1,177

I took this this morning when I woke up (5am) exposures is Lum 10 secs  RGB 30 secs, only took a few about 40 mins worth in total, I was doing the jellyfish nebula and still in the middle of processing it now. In my eagerness I took it in LRGB plus Ha and Oii I have only combined Ha to RGB before (in scripts MRGB combination) so no idea how to merge all these yet

untitled.jpg

Share this post


Link to post
Share on other sites
spillage    302

This really is my first time at mono. Really messed up and only ended up with RGB so no L or Ha,O111 or S11. Also I did not take any darks.

This is 15 sec subs at unity x20 so 15 min total exposure time. Focus is out and stars seem a bit out of shape.

Orion_RGB.jpg

  • Like 1

Share this post


Link to post
Share on other sites
brrttpaul    1,177

you messed it up?? I messed it up spent the last 5 hours going through all the data from last night, ended up with 47 gb and I had done the HA 120 secs , way to low i think, or i fluffed it up somewhere

Share this post


Link to post
Share on other sites
spillage    302

I know M42 is a bit of a cheat but I did a couple test shoots in Ha at 30sec that I deleted and they seemed okay.

Edited by spillage

Share this post


Link to post
Share on other sites
RichLD    737
On 06/09/2017 at 06:44, wimvb said:

From what I've seen on the internet (having just bought a zwo camera myself), you can either go with high gain+offset and short exposure times, or with 0 gain (10 offset) and long guided exposures, 300 to 600 seconds. I've seen very impressive results with the latter. Total time on target doesn't vary much though. This means either lots of short or fewer long exposures. With the file size of the asi1600, I'd personally prefer fewer exposures.

+1 

I tend to go with 600s exposures at around unity gain with the QHY163m on NB and am very pleased with the results. :thumbsup:

Share this post


Link to post
Share on other sites
brrttpaul    1,177

yeah im gutted first fully clear night where everything worked and my Ha exposures were ony 120 secs and didnt pack no punch at all, never mind I will learn from it

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

×