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M51 in poor seeing - 2000*1s ASI1600mm-cool

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#1 MvZ

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Posted 08 May 2016 - 06:10 PM

Hi All,

 

I recently got a chance to play around with the ASI1600MM-Cool camera. Because the chip is much larger than what I'm used to, I used a skywatcher 0.9x coma-corrector. I might need to do some tweaking still to get it in the perfect position, but for now it already seemed to produce a pretty flat field. 

 

In order to reach focus I had to mutilate the plate the focuser is positioned on, right below the top ring of the 16" Dobson, and move it forward 4cm. I messed up the exact position though, so this is definately something I want to look at later, but for now it works 'OK' with some tweaks to get decent colimation again. I also created a hand-controller for my EQ platform that can be connected to the Arduino driving the EQ platform tracking motor. It works very nice, it's much easier to control everything with 'real' buttons instead of using the laptop touchpad...  My soldering skills - like my ATM skills - are not that good, so it takes a bit of time, but the programming of the Arduino software is a bit easier for me. I didn't manage to motorize the declination control, I need to think this through. I'm getting used to the manual declination control anyway.

 

The ASI1600MM camera seems to work very well. Judging from this recording - containing only 34 minutes, with exposures of just 1 second each - the depth is already pretty impressive. I'm quite happy that I can do live-focusing at 10fps (and full res) without any problems; I like my camera's fast. This is also the first time I had a camera in my hands that can do cooling - which is probably not needed for 1 second exposures, but perhaps it will be during warmer nights (and for sure when using longer exposures), but I'll test the dark-current to be sure in the following weeks. The cooling is easy to use anyway, and it should help at least a tiny bit, so in the end I decided to just use it for now anyway (I set it to -15C, which it reached within a minute or so, and then it stayed there during the rest of the night... ). 

 

Processing 40GB of data really is quite a challenge. So far AutoStakkert! manages to plow through it though, and stacking with two-pass sigma-clipping (.. I didn't know there were that many satellites out there!) took about 20 minutes. Without sigma-clipping it should take around 10 minutes I think. Either way it will take a bit of patience to find the correct settings; I certainly wanted to try different processing techniques to figure out how everything was working. In the end I think post-processing (and writing this message..) took more time though, so the stacking time is still acceptable to me. 

 

Unfortunately the seeing wasn't very good, so I had to downsize the final image to get a reasonably sharp-looking image. The short exposures already help quite a bit with keeping the stars smaller though. A day before the seeing was much better, but I was stupid enough to not really make many recordings then (a few minutes worth of M13, and a few other targets with similar total exposure lengths. I still need to process them, but it will take quite a bit of time).

 

p.s. I don't want to start a discussion here too on CMOS v.s. CCD sensors, the future of deepsky imaging, # of APODs, and more stuff like that. Any other comments or remarks are certainly more than welcome though!

 

P.s. Click here for a better  (less compressed) version of the image: http://www.astrokraa...l_Kraaikamp.jpg
 

Attached Thumbnails

  • 20160505_M51_2000x1s_AutoStakkert_ASI1600MM_Emil_Kraaikamp_2.jpg
  • IMG_20160508_200023.jpg

Edited by MvZ, 09 May 2016 - 03:13 AM.

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#2 WhitenerJ

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Posted 08 May 2016 - 06:19 PM

Excellent detail from this camera. WOW!!

 

Jason



#3 Thirteen

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Posted 08 May 2016 - 06:43 PM

I'm glad to see those faint objects in 1s exposures. So cool to not have to care about guiding, except for long term drift. Good work, did you come across any concerning pattern noise?

Edited by Thirteen, 08 May 2016 - 06:45 PM.


#4 james7ca

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Posted 08 May 2016 - 06:50 PM

Emil, that looks somewhat similar to what I got with an ASI178MM-Cool in 2 hours under my red-zone light pollution with a 5", f/5.2 refractor.

 

  http://www.cloudynig...-3#entry7137761

 

In any case, on your coma corrector, can you remove the 2" eyepiece stop ring and extend the comma corrector farther into your focuser? I had to do that with a Baader MPCC on a 6" Newtonian so that I could reach focus without having the focus tube extend down into the path of the primary mirror (by removing the stop ring and adding an M48 extension tube to the coma corrector I was able to move the camera closer to the primary mirror). I don't know if you can remove the stop ring on your coma corrector, but it sounds like you had a problem somewhat similar to what I had (before my "fix"). 



#5 jgraham

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Posted 08 May 2016 - 07:08 PM

Wow, excellent result. How dark and transparent was your sky?



#6 jhayes_tucson

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Posted 08 May 2016 - 07:36 PM

That's a very impressive image for only 34 minutes of total exposure time!

 

John


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#7 MvZ

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Posted 09 May 2016 - 04:54 AM

>Good work, did you come across any concerning pattern noise?

No fixed patterns as far as I could tell; there is some horizontal line noise, similar to other CMOS sensors (the IMX174 for example). I haven't done any test to measure the amount of this noise, but from a very rough guess I'd say it is comparable,

 

>Emil, that looks somewhat similar to what I got with an ASI178MM-Cool in 2 hours under my red-zone light pollution with a 5", f/5.2 refractor.

Excellent, very nice result! This is why I say the seeing wasn't good; I know there are many details to be gained if the seeing cooperated a bit more, my previous M51 shot already was a lot sharper. But still, it's not too bad, and I was pleasantly surprised by the 1 second exposures already showing much of the fainter stuff.

 

>In any case, on your coma corrector, can you remove the 2" eyepiece stop ring and extend the comma corrector farther into your focuser?

 

I think it is fixed, otherwise I would have done this. But to be honest, I wanted to change the focuser anyway, because at one point or another I really like to be able to use a color wheel for recordings like this.

 

>How dark and transparent was your sky?

I could faintly see the milky way later in the night, bu have seen better here. There were some thin high clouds now and then. I don't have a SQM value.



#8 bilgebay

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Posted 09 May 2016 - 06:45 AM

Very cool! Thanks!



#9 TheRock

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Posted 09 May 2016 - 07:55 AM

Emil, thanks for sharing this wonderful image. Can you share some more information about the file processing that took place? Of concern is the large files sizes and the amount of free disk space to store them. What kind of processor/PC are you using? Thanks.


Edited by TheRock, 09 May 2016 - 08:32 AM.


#10 josh smith

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Posted 09 May 2016 - 08:24 AM

Looking quite nice!  Especially for short exposures and poor seeing.  Glad to hear the stacking is not much of an issue and seems pretty automated.  Are you able to use flats and how do you apply them in this kind of imaging?  How about bias or dark frames or are they just not needed?



#11 AdrianoMS

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Posted 09 May 2016 - 09:37 AM

Very nice image of M51.



#12 AstroCatinfo

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Posted 09 May 2016 - 02:45 PM

Spectacular. This camera starts to show it's potential.



#13 Jon Rista

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Posted 09 May 2016 - 04:02 PM

Emil, the image looks great. Really great for poor seeing, which is exactly what I am looking for.

I do have a question, if you do not mind. How are you aligning with AS!2? Are you aligning on certain stars? Or do you just automatically add alignment points like you would with planetary?

#14 Peter in Reno

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Posted 09 May 2016 - 04:17 PM

Using Lucky Imaging is going to be a new ball game for DSO video imaging. What about calibration with dark, bias and flat? Also, will dithering be no longer necessary?

 

Peter



#15 rmuhlack

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Posted 09 May 2016 - 06:45 PM

Great image Emil! This camera certainly shows a lot of potential. Can you tell us what gain setting you used, and if the frames were dark/flat/bias calibrated? Also, did you collect more than 2000 frames so you could reject those affected by particularly poor seeing, or did you stack all the frames that were collected?

 

Richard



#16 hytham

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Posted 09 May 2016 - 07:56 PM

Excellent work, Emil.

 

Let's be honest for a moment though... your processing skill definitely helped highlighting the detail.

 

Do you have any plans on going after fainter targets? I'd like to see how well the camera would fare in that scenario (though most of us readily know the answer, it's interesting to see the result).

 

Thank you for sharing.



#17 buckeyestargazer

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Posted 09 May 2016 - 08:29 PM

Do you have any plans on going after fainter targets? I'd like to see how well the camera would fare in that scenario (though most of us readily know the answer, it's interesting to see the result).

 

Thank you for sharing.

+1



#18 JMW

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Posted 09 May 2016 - 09:02 PM

If AutoStakkert! can handle field rotation short exposure imaging could be done on a alt/az mount such as a ServoCAT enabled Dob. Did you should the 1 second exposures as video or individual exposures?

 

The newest version of the ServoCAT software can stay locked on a target. I will have to try the ASI1600 cooled on my Webster D14 with ServoCat and f/4.3 14.5 inch Zambuto mirror. I will be at the GSSP under very dark skies at the end of June.


Edited by JMW, 09 May 2016 - 09:05 PM.


#19 MvZ

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Posted 10 May 2016 - 07:22 AM

Many questions, and as many answers..

>thanks for sharing this wonderful image. Can you share some more information about the file processing that took place? Of concern is the large files sizes and the amount of free disk space to store them. What kind of processor/PC are you using? Thanks.

 

Processed with my own software (surface mode, align on one single star). I had two recordings actually, each about 20GB in size that I stacked separately. I combined them manually in Photoshop. The PC was an i5 with 8GB ram, Windows 7.

 

>Are you able to use flats and how do you apply them in this kind of imaging? 

I'm able to use them, but haven't used them. I always do artificial flat-field correction in Photoshop, but perhaps will try the real-deal as well... Still, I think artificial flat-field correction is quite important to get rid of the smallest gradients. It makes stretching the data much easier.

 

>How about bias or dark frames or are they just not needed?

I always use a matching set of darks, and turn it into a master dark that I apply to the image (so it has the bias-information included).

 

>How are you aligning with AS!2? Are you aligning on certain stars? Or do you just automatically add alignment points like you would with planetary?

Always just on one star with one AP. Don't use multiple alignment points for DS. No easy way to detect field rotation is supported though (well, if you know the rotation from frame one to the last frame in your data set, you can enter this angle manually and it will apply it for you)

 

>Also, will dithering be no longer necessary?

Ehm; I have automatic dithering; my platform tracks poorly (and my polar alignment is not so good either) ;). I would always do dithering, it makes the resulting stacks clean (and it avoids having a slightly imperfect master dark with some random noise still turn into a fixed pattern noise!)

 

>Can you tell us what gain setting you used

I used 350 or so (35dB), but I think I could have stopped at 300 (the maximum analog gain for lowest effective read noise)

>and if the frames were dark/flat/bias calibrated?

Dark (bias information is part of the dark), no flat. I used about 400 dark frames and turned them into a master dark.

>Also, did you collect more than 2000 frames so you could reject those affected by particularly poor seeing, or did you stack all the frames that were collected?

I recorded about 2800 or so frames. So there was very little selection going on (only some brighter or very faint frames and the most distorted ones were discarded)

 

>Let's be honest for a moment though... your processing skill definitely helped highlighting the detail.

Thanks. Processing is of course always extremely important. You can have a really expensive setup and perfect seeing, and still get crappy images; I always try to push the processing quite far, which means the image isn't as clean as it could be in favour of some more fainter stuff that becomes visible. I don't mind a little bit of noise, especially not when it comes with a bit more sharpness.

 

>Do you have any plans on going after fainter targets? I'd like to see how well the camera would fare in that scenario (though most of us readily know the answer, it's interesting to see the result).

Probably. I would need to expose for a longer time, and I don't have a setup that can do that all over the sky. I will try it on a target near polaris to minimize the tracking errors. Perhaps I can push it to 5-10 seconds or so with reasonable resolution still. The weather is always a problem though.

 

>Did you should the 1 second exposures as video or individual exposures?

Video, well, SER format and in 8-bit/pixel actually. I don't care about dynamic range it is destroyed by the high gain setting, so 8-bit is enough to represent all the signal. The quantization noise from not using 12-bit is tiny compared to everything else. The master dark of course is 16-bit though, and stacking is internally mapped to 32-bit (a bit more actually) and only when saving the stack it is turned into a 16-bit stack (which is again more than enough for this type of imaging).


Edited by MvZ, 10 May 2016 - 07:22 AM.


#20 JMW

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Posted 10 May 2016 - 10:30 AM

You could could the drizzle feature in Nebulosity to align all the frames to account for field rotation and then use AutoStakkert! to stack the frames. That would work for FITS files, not sure about  SER video.



#21 calypsob

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Posted 10 May 2016 - 10:39 AM

Wow, did not know you used ser. I tried tiffs, it was difficult to get good images with the c11. I hoped to use dss to register the images but there was only one star when I shot the sunflower galaxy last weekend. I hoped to sort the images by fwhm and stack. It didnt work so I went to as!2. As!2 i found does not de rotate images after meridian flip so I need to manually rotate first then stack. Emil, do you have a tutorial for creating you artificial flat in ps?

Edited by calypsob, 10 May 2016 - 10:40 AM.


#22 josh smith

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Posted 10 May 2016 - 10:41 AM

So for master darks and flats, you just use them on the stacked image instead of the individual frames?



#23 MvZ

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Posted 10 May 2016 - 11:09 AM

>So for master darks and flats, you just use them on the stacked image instead of the individual frames?

No, of course not, that wouldn't work, there is a lot of movement from beginning of the recording to the end. Each frame is calibrated first, only then it is aligned and stacked. This is done inside AS!2 though.

 

> Emil, do you have a tutorial for creating you artificial flat in ps?

I first learned it from some youtube video a long time ago. Not sure if there is a tutorial, but it comes down to the following steps:

Create two copies of the stack as layers (you should have already stretched the stack quite a bit so you can see the gradients), remove everything except the gradient in this image (using dust & scratches in photoshop at a large radius, and lots of careful clone-stamping to mask out the target of interest.. go back and forth between the original and the flat you are making to see if you are on track). Finally, blur this flat a lot, typically I use a gaussian blur with something like 80 pixels in size. Invert the image, and blend it back in with the stack with an opacity of exactly 50. Then merge these layers down, and bring back the black point to almost half-way again.

 

There are limitations;

- Make sure you do this on cropped stacks, the gradient has to be smooth..

- It works only on a select number of targets; they should not be too big, it does not work on extended objects.

- It does not remove any dust particles, it's really only for removing large gradients. Just make sure your sensor is clean ;)

 

I simply have never done any real flat-fielding. Perhaps a bit too lazy, but I also know the sky gradient is often still messing things up a bit (or some clouds introducing some new gradients, etc), so I just go with an artifical flat only.


Edited by MvZ, 10 May 2016 - 11:10 AM.

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#24 Jon Rista

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Posted 10 May 2016 - 11:44 AM

Emil, how do you do flat correction in AS!2? I wasn't aware it was capable of doing that. I was planning on doing dark subtraction within FireCapture or SharpCap, then flat calibration "at some other time"...but I hadn't quite figured out how. If AS!2 can do it, that would be perfect. 


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#25 MvZ

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Posted 10 May 2016 - 11:54 AM

There is a menu image calibration -> load master flat (and/or dark), that should work*. It shows a bright yellow label in the information section of AS!2  if the flat or dark is being applied correctly. The dimensions of course have to be exactly the same. I suggest you create the master frame via AS!2 as well from the same menu.

 

*but perhaps not in some older versions of AS!2. Try the latest beta.


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