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4 second exposures ASI174MM + 16" Dob - M51 and M57

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#26 Peter in Reno

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Posted 20 June 2015 - 09:43 PM

A cooled ASI174 would be nice. I don't know the dark noise in ASI174 but my new ASI120MC-S shows significant increase in dark noise for around 5 seconds as compared to 33 FPS (very short exposure). It does not really have to be regulated cooling. I have seen people adding peltier cooler, heat sink and fan to the back of ASI camera and showed a significant reduction in dark noise.

 

Peter



#27 cguvn

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Posted 21 June 2015 - 08:38 AM

Unreal. Holy crap this is good


Edited by cguvn, 21 June 2015 - 08:40 AM.


#28 MvZ

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Posted 22 June 2015 - 04:25 AM

Thanks. I'll probably look into cooling the camera's as well, but it will likely only be passive cooling, since I doesn't make sense to take long subs with my equipment.

 

The list of Frank makes sense, I started doing this short exposure deepsky with my Starfinder EQ telescope + (poor) mount out of budgetary reasons; I simply did not have the equipment to do long exposures (mount tracked very poorly, I only had uncooled or passive cooled modified webcams to work with, etc), but I quickly noticed the good things as well: sharp subs, option to filter out the bad ones (I typically rejected at least 50% of the frames).

 

But there are downsides too of course:

- You still don't catch enough photons for the weaker regions of the images to get above the read noise of the camera, so you basically can't go very deep. It works best for the bright(er regions of) deepsky targets.

- Processing can be a pita (many thousands of frames to sift through, currently working on making AS!2 more robust for very low signal subs)

 

It might be interesting to combine the two approaches; lower res but high signal/noise for the dimmer regions + high res of the brighter areas.

 

(hmm. I wan't to talk less and do more imaging. The weather forecast is still terrible here)


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#29 Vars191

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Posted 28 June 2015 - 10:11 PM

It has been a while since my last deepsky attempts, but two nights ago I had some nice clear skies at my observing location, so I decided to visit some well known (and less known) targets. Both images contain about 30 minutes worth of 4 second exposures with a 16" Dobson (Rik ter Horst optics) and ASI174MM camera.

 

I had some trouble with coma, but when I try to use the coma corrector, I can't seem to reach focus at the moment (I need to move the focuser slightly inwards, there should be some room for this).

 

Anyway, the central part of the image was quite ok, and with the short 4 second exposures most frames were pretty sharp to begin with too (e.g., tracking is more accurate, so no need for auto-guiding, and the seeing effects are also quite small in shorter exposures). I certainly plan to do some more deepsky work in the future.

 

Both M51 and the luminance of M57 are without filters. For M57 I had to manually screw in and out some astronomik RGB filters because my filterwheel is too thick to go in front of the camera (again, the focus issue). I should have done this for M51 too, but the nights are really short, and I also wanted to image two other more obscure (and less attractive) targets. I will try to capture some color next time.

 

How does it compare with the ASI224



#30 MvZ

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Posted 01 July 2015 - 04:13 PM

Short answer: I don't  know, I'll have to wait and see.

 

 

Slightly longer:

 

I'll probably prefer the (much) larger pixel size of the ASI174 in general, but I certainly need to do more testing with both camera's for both deepsky as well as planetary imaging.

 

The 3.75um pixels of the ASI224 are ... ehh... challenging at 2 meters focal length. But the low read noise might make up for this as I can use shorter exposure times still.

 

It might take a while though; I'm away for the most part of the next three weeks, and I haven't had a chance to do imaging in the last few weeks... The camera's are basically just waiting for more light.



#31 Joe Bruessow

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Posted 14 July 2015 - 12:39 PM

MvZ...

 

I have been out of imaging for several years... and have just pondered getting back into it.  Wow!  Your images have me amazed at what stacking so many images can do with such short exposures.  The asi174mm seems such a versatile camera for what I might like to try.  I have a 20" Obsession with Servocat, and you have me wondering if I could pull this off for galaxy imaging... I just don't know about how long I can go before tracking or field rotation would be an issue.  

 

Is there a particular website I could refer to that describes the workflow (including software packages) for this type of imaging would be helpful.

 

Thanks for getting me enthused about getting back into this!



#32 Hbeing

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Posted 20 July 2015 - 03:01 PM

What software are you using for the long exposures.?

 

Thanks

 

Peter



#33 MvZ

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Posted 04 September 2015 - 05:31 PM

Sorry for not responding earlier. I remember reading the messages but had waited to reply for some reason...

 

>Is there a particular website I could refer to that describes the workflow (including software packages) for this type of imaging would be helpful.

Not that I'm aware of actually. I have been doing this type of imaging since 2007 or so, because my mount (and camera) simply couldn't do longer exposures, but I basically figured it out on my own. I'm a planetary imaging guy, so the software that I'm using for recording is FireCapture. 

I use AutoStakkert!2 for processing, but this can be really tricky at times as it can be a bit of a black-box and difficult to figure out where and why things go wrong. If it doesn't go wrong though, it is pretty fast and can have good results too. It helps that I can make some changes to the software while processing new recordings. I'm currently testing out an algorithm that removes the horizontal banding noise in the ASI174MM camera that is very faint but does always show up when pushing the data to the limit. This allowed me to go back to some earlier recordings and really push the data hard.

 

Attached a latest reprocessing of M51 using AutoStakkert!2 and Photoshop for post processing. Same data (actually I added a few frames more, 75% of what I collected that evening, so about 37 minutes integration time now).

 

I might write a small tutorial on how to make and process recordings like this, but currently I prefer to my spare time into actually making and processing recordings, and working on AS!2.

 

>I have a 20" Obsession with Servocat, and you have me wondering if I could pull this off for galaxy imaging... I just don't know about how long I can go before tracking or field rotation would be an issue.

A 20" could be very nice for this. Just try things out. There is no fully automatic field-rotation compensation in AS!2, but there is some functionality that you might use (although I would wait for a newer version of AS!2 to come out soon that will be better for this work. Other stacking software might also work, but typically the frames are difficult to deal with).

 

(better version here: http://www.astrokraa...1_reprocess.jpg )

Attached Thumbnails

  • M51_new.jpg

Edited by MvZ, 04 September 2015 - 05:33 PM.

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#34 DaveB

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Posted 04 September 2015 - 06:48 PM

Apologies if this was mentioned in the thread somewhere (I didn't see it) - is your dob motorized somehow, i.e. with an eq platform or even some alt-az motors?



#35 MvZ

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Posted 05 September 2015 - 03:41 AM

The Dob is on an EQ platform, but I suspect with an alt-az it would be possible to get good results too (rotating the images during stacking), as these short exposures won't show field rotation I guess.



#36 Mert

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Posted 07 September 2015 - 07:40 AM

Hi Emil,

 

Great results, very good!!

Could you please share a couple of settings you used with the ASI174??

IMHO they could be used for the 224MC as well.

 

Do you use a high gain setting??

 

Best regards,

Mert



#37 MvZ

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Posted 08 September 2015 - 04:10 AM

I'm not sure about the settings Mert, but I probably had the gain at about 300 (which is quite high, but not the highest available setting). Read noise is lower for higher gain settings, but there is pretty much no difference in read noise between a 300 or 400 gain value. So then it makes sense to go for the higher dynamic range and use 300 instead. I probably could have gone to 200 as well, but at 300 there was pretty much nothing visible that was over-exposed anyway.

 

For the 224 I would probably stay at around 300 as well (it can go higher, but you'll easily over-expose something then). It depends on your exposure time of course; just make sure that you do not over-expose what you are interested in. A star that is a bit too bright, who cares, but the center of a galaxy or some part of a planetary nebula that is over-exposed is not very nice. For very short exposures like these you should probably never use the lowest gain setting.



#38 Mert

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Posted 08 September 2015 - 11:38 AM

Makes a lot of sense Emil!

Lately I did a lot of testing with the 224 almost always using

a gain setting of aprox. 250.

Exposure ranges from 3 to 5 ( even 10 ) seconds.

Unfortunately the Amp-glow is very heavily present but evenso

this little camera gives me much more red-sensitivity then my

DSLR ( unmodified )

IMHO the exposure at aroud 2 to 3 seconds is high enough to grab

very faint stars as well, so making many subs will give nice results.

 

I'm looking forward for the beta versiĆ³n to use for stacking DSO work.

 

Thanks for your feedback, much apreciated!

Mert



#39 Gabor Kiss

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Posted 10 October 2018 - 03:17 AM

I'm not sure about the settings Mert, but I probably had the gain at about 300 (which is quite high, but not the highest available setting). Read noise is lower for higher gain settings, but there is pretty much no difference in read noise between a 300 or 400 gain value. So then it makes sense to go for the higher dynamic range and use 300 instead. I probably could have gone to 200 as well, but at 300 there was pretty much nothing visible that was over-exposed anyway.

 

For the 224 I would probably stay at around 300 as well (it can go higher, but you'll easily over-expose something then). It depends on your exposure time of course; just make sure that you do not over-expose what you are interested in. A star that is a bit too bright, who cares, but the center of a galaxy or some part of a planetary nebula that is over-exposed is not very nice. For very short exposures like these you should probably never use the lowest gain setting.

Dear Emil,

 

I believe this thread is very interesting to read over and over, I've seen you made pictures with the ASI 1600 cooled camera as well. What are your experiences after your last post?

 

Still stacking in AS3! - what are your experiences compared to the Deep-Sky Stacker (if you have any)?

 

With the cooled cam, can you go with longer exposures on fainter objects, or still trying to "lucky-imaging" for higher resolution?

 

All the best,

Gabor


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