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DSO test shots using an ASI224 and a Goto Alt Az mount

astrophotography ccd dso EAA imaging
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#1 Astrojedi

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Posted 04 August 2015 - 03:04 PM

Some experimental DSO test shots using an ASI224 and a Goto Alt Az mount.

ASI224 is stated to be a very low read noise camera (<1-2e) with high sensitivity (peak QE 70-80%). Hence wanted to see what results I could get with <5 sec subexposures.

Another motivation is that on most weekdays I usually don’t bother setting up the EQ mount as I usually only have 1-2 hours of observing time. I know the results will not match long exposure photography but wanted to see if this camera could provide an acceptable compromise for these sessions... almost like a hybrid imaging/EAA experience.

 

Setup

Nexstar 8SE Goto Alt Az 8” SCT scope at f/4-f/5 and the ASI224 connected to my Surface tablet

Software used was FireCap (to capture FITs), DSS (for stacking) and Photoshop Lightroom & RAW Therapee for basic stretching and color balancing (kept processing to a minimum).

 

Some initial observations:
• The camera is very sensitive. In live view with gain at 300-400 I regularly see up to 14 mag stars

• Even short exposures produce enough SNR for reasonable results vs. my DSLR and CCD which produce a sea of noise at 1-5” subexposures 

• I found that for certain DSOs I have to image at a 300+ gain to ensure I have enough stars for DSS to align but as a result I am definitely losing information to clipping even after stacking hundreds of frames

• Maybe with a larger scope (12-16”) I could get away with using a lower gain but I don’t have one so no way of confirming

• The camera I have seems to be exhibiting high amp glow from the electronics at all gain settings. The impact gets really amplified when you stack hundreds of frames (vs. tens of long exposures frames where the SNR is much higher) EDIT: using max for stacking dark frames and lower gain mitigates this to an extent but certain DSOs with limited bright stars in FOV are challenging to stack.

• Stars appear a little blobby even after I have checked focus multiple times (using both FWHM and a Bhatinov mask). Maybe an IR cut filter could mitigate this given the high IR sensitivity of the camera. Tried using my Meade IR filter in front of the Antares 0.5x FR but getting reflections likely due to the high FR being applied. Need to figure out a solution here.

 

My initial takeaway is that there is potential here but issues exist (may just be due to my lack of expertise or maybe I am just asking for too much and technology just hasn’t caught up yet :) ).

All comments/insights/guidance welcome...


Edited by Astrojedi, 06 August 2015 - 09:30 AM.


#2 Astrojedi

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Posted 04 August 2015 - 03:09 PM

First up is the M27 without any calibration frames (100x 3" gain 260).

 

M27 ASi224

 

 

The M27 with dark calibration frames. A very acceptable image for my purposes. Mitigated most of the Amp glow using dark frames, image showing medium detail. Still a little noisy. (100x3" gain 260 and 10x3" darks)

 

M27 100x3s G260 D15 ASI224
 
Edit
Wanted to add that all of these have been taken from my suburban backyard with significant light pollution (5-6 on the Bortle scale). Moon was between 20% - 60% over these few days.

Edited by Astrojedi, 04 August 2015 - 03:20 PM.


#3 Astrojedi

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Posted 04 August 2015 - 03:11 PM

M80 lights 500x1", darks 20x1", sensor temp pretty stable throughout, gain 300

 

M80 500x1s G300 ASI224


#4 Astrojedi

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Posted 04 August 2015 - 03:15 PM

M15 lights 100x2.5" darks 10x2.5" gain 250

 

M15 100x2.5s G250 ASI224

 

 

Will post more results later today including M101 and M102...



#5 Astrojedi

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Posted 04 August 2015 - 03:34 PM

M101 (light 430x3", dark 20x3", gain 400)

 

One of my favorite galaxies to image. Getting detail in the arms needs long total exposure and is a good test for sensitivity but here I really struggled with amp glow (even after using 20 darks) at 400 gain.

 

My guess is that this is due a combination of the high gain setting and the intrinsically lower SNR from this approach and/or the fact that I took the darks at the end of the imaging session during which the sensor temp fell from 29deg to 26.5deg Celsius. Also potentially stacking so many frames is making this worse.

 

Maybe regulated cooling could help here but I need to run more tests to investigate the reason for this. Always possible that I am doing something wrong.

 

M101 001

Edited by Astrojedi, 04 August 2015 - 03:53 PM.


#6 Astrojedi

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Posted 04 August 2015 - 03:50 PM

M51 shows the same amp glow issue at 400 gain... just can't get rid of it...

 

Lights:18x5s darks:10x5s gain 400

 

M51 18x5s G400 10x5s darks

Edited by Astrojedi, 04 August 2015 - 03:54 PM.


#7 Astrojedi

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Posted 04 August 2015 - 04:01 PM

M102 lights: 133x1s, darks: 10x1s, gain 400

 

M102 133x1s G400 darks 10x1s


#8 wenjha

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Posted 05 August 2015 - 03:33 AM

just a little weired why some image the amp glow is so obvious

and some image are so dark

 

and cannot subtract with dark?



#9 Astrojedi

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Posted 05 August 2015 - 12:42 PM

Yes, the dark frames did not help here.

 

I am guessing the problem is a combination of a few factors... I took the darks at the end of the session by which time the sensor temperature had dropped ~2 degrees and second that stacking 400+ frames just amplifies the glow not eliminated by the darks (I think even more pronounced as the SNR is lower vs. a longer exposure). A very high gain setting probably does not help either.

 

To check this hypothesis I imaged M101 again last night, but this time shot at lower gain, increased exposure time to improve SNR and took the darks before and after the session to compare. Not had a chance to process yet but will post the results later today.


Edited by Astrojedi, 05 August 2015 - 12:43 PM.


#10 Astrojedi

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Posted 05 August 2015 - 08:05 PM

Ok. Managed to to resolve the issue after some trail and error.

 

The fix involved:

 

1. Lowering gain from 400 to 250

2. Taking darks before the imaging session (when sensor temp was the highest)

3. Using 'Maximum' to combine dark frames in DSS instead of 'Median'.

 

Surprisingly #3 had the most noticeable impact followed by #1 and then #2.

 

M101 420x4s 15x4s before darks Max G250

 

M101 (420x4s lights, 15x4s darks, gain 250)

 

Slightly better color balance... less aggressive stretch

 

M101 420x4s 15x4s before darks Max G250 2x drizzle

Edited by Astrojedi, 06 August 2015 - 12:39 AM.


#11 wenjha

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Posted 05 August 2015 - 08:57 PM

Ok. Managed to to resolve the issue after some trail and error.

 

The fix involved:

 

1. Lowering gain from 400 to 250

2. Taking darks before the imaging session (when sensor temp was the highest)

3. Using 'Maximum' to combine dark frames in DSS instead of 'Median'.

 

Surprisingly #3 had the most noticeable impact followed by #1 and then #2.

 

 

 

M101 (420x4s lights, 15x4s darks, gain 250)

 a great improvment

4s is still very short for M101 which is a dim object

 

cooled 224 would help under such condition ;)



#12 Astrojedi

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Posted 06 August 2015 - 12:35 AM

Thanks Sam. Would love to have a cooled camera with read noise as low as the ASI224 but with an ASI174 sized sensor :).

 

IMO the read noise is a game changer. While I never expect the results from such short exposures to match long exposure imaging, the sub 5 sec exposures do show how much read noise matters. Will be interesting to see what a cooled camera can do.



#13 Astrojedi

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Posted 09 August 2015 - 12:34 PM

Lagoon Nebula from last night... heavy light pollution looking towards the city... Could not see stars fainter than mag 3.

 

Lights 100x4s Darks15x4s Gain 302 (@ ~f/3.7)

 

M8 L100x4s D15x4s Max Gain 302

Edited by Astrojedi, 09 August 2015 - 01:38 PM.


#14 Astrojedi

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Posted 09 August 2015 - 12:47 PM

M20 The Trifid Nebula from last night... also in the same heavy light pollution looking towards the city...

 

Lights 100x4s Darks15x4s Gain 244 (@ ~f/3.7)

 

M20 L100x4s D15x4s G244

Edited by Astrojedi, 09 August 2015 - 01:38 PM.


#15 Astrojedi

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Posted 09 August 2015 - 01:40 PM

M17 The Swan Nebula

 

Lights 100x4s Darks 15x4s Gain 302 (@ ~f/3.7)

 

M17 Swan L100x4s D15x4s G302


#16 David B in NM

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Posted 09 August 2015 - 05:01 PM

Nice images Astrojedi,

 

If you have ASCOM support for the 224 you may want to think about this program.  It should do it all nearly live on-the-fly.

 

http://astroprecisio...ucts/astro-live

 

David B in NM


Edited by David B in NM, 09 August 2015 - 05:01 PM.


#17 wenjha

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Posted 09 August 2015 - 09:30 PM

very nice!

is the star problem because of Alt Az mount?



#18 Mert

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Posted 10 August 2015 - 05:27 AM

My hat is off for you Astrojedi,

 

Here you have a sample of M13, taken 080815 with my Mak 6" with 0.5x reducer

and the ASI224MC.

This image is composed of 42 frames of 5 seconds each, stacked

with DSS and processed with Pixinsight.

Autoguided with PHD2 with ASI120MC plus ZWO guiding tube,

guides like a clock!

The stars are a little bit bigger then usual due to imposible seeing.

 

Regards,

Mert

Attached Thumbnails

  • M13_ASI224_F6,5.jpg


#19 Astrojedi

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Posted 10 August 2015 - 02:04 PM

David,

Appreciate the comments. I tried the 30 day trial version of Astrolive but could not get live stacking to work properly for me (it was not able to align images and the stack turned in to a blur). Also many image manipulation controls were disabled.

 

Sam,

Yes, the alt az mount is a factor. Also the aggressive focal reduction used is potentially causing the stretching towards the edges of the frame.

 

Mert,

That is a very nice image. Like the blue and yellow colors. What gain setting did you use?

 

Hiten



#20 DonBoy

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Posted 10 August 2015 - 03:33 PM

Astrojedi,

 

Impressive results from the ASI224.  Have you tried AstroToaster (it's free).  It is a stacking program that uses DSS as it's engine.  I've tried DSSLive and find it comber sum.  I used AstroToaster with an Atik 414EX color to demonstrate that it could be used for NLI (near live imaging) and broadcasted the images on NSN. 



#21 David B in NM

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Posted 10 August 2015 - 05:24 PM

Hiten,

 

Sorry to hear AstroLive gave you problems.  Software for higher resolution EAA is pretty limited. 

 

Don made a very good suggestion above.  It'll be interesting to see how things work out well for you. 

 

I will say the 224 shows great promise for EAA.  If possible, can you take two images of each target?  One with the "stack number" you prefer for "imaging quality" and another with about 50 to 75 percent of the "image quality" capture stack.  For EAA the goal of many people is not "image quality captures" but an acceptable image in as brief of a period as possible.

 

Thanks!

 

David B in NM



#22 Astrojedi

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Posted 10 August 2015 - 05:59 PM

Thanks for the suggestion Don. I have actually tried AstroToaster in the past for DSLR live stacking. Will try it with the ASI224.

 

David,

 

See my post here in the EAA forum: http://www.cloudynig...20#entry6723601. I think that post partially addresses what you are looking for.

 

Although I used a smaller subset of the same subexposures in the images I posted on the EAA forum, the real difference in results is due to the calibration and post processing steps (the camera is very sensitive).

 

If the skies stay clear tonight I will do the EAA version using AstroToaster and post the results and a comparison soon.

 

Hiten



#23 David B in NM

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Posted 10 August 2015 - 06:21 PM

Hiten,

 

Thanks.  Your link in that post is what brought me here.  Normally conversations about images take place in threads so the EAA Gallery is mainly images.  I'm guessing Don found this thread the same way.

 

It'd be nice if you continued to post the EAA-type images in the Gallery or maybe even think about starting a thread for the use of the 224 in the EAA Forum itself.  Pictures are allowed in discussion threads in the EAA Forum for "new" cameras.  IMHO the 224 is a new camera that does show it may be useful for EAA.

 

Recently Atik and SX have announced new EAA cameras (their first EAA cameras).  Neither is cooled.  A cooled 224 may be the ticket for some in EAA since higher gain may be used. Your pictures demonstrate this with an uncooled camera.

 

David B in NM



#24 Stargazer3236

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Posted 10 August 2015 - 07:12 PM

Astrojedi, what do you think is the better camera, the ASI224MC or the ASI178MC? I have my eye on the latter because of the 6.3mp resolution, low read noise @ 2.2e and high sensitivity and low pixel size @ 2.4 um per pixel.

 

When you take your shots, are you taking 100 individual frames at 3 seconds each, then stacking them in post processing? 

 

When you take your darks, are you capping the end of the telescope, then taking 15 individual frames at three seconds each?

 

I am new to imaging and trying to get a handle on the steps to take to take and process images.

 

Recently I have been using the Neximage 5 webcam to take planetary pics, but now want to take it a step further into another stage to get better planetary pics and DSO's.

 

Dave


Edited by Stargazer3236, 10 August 2015 - 07:23 PM.


#25 Stargazer3236

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Posted 10 August 2015 - 07:18 PM

Also, which software do you use to capture your images?




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