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Testing capture with short exposures / F10

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#1 SanjeevJoshi

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Posted 21 January 2021 - 03:01 AM

Tonight was average seeing and getting worse as the evening progressed.   I tested out my earlier target -- M1 using the following set up for short exposures and high gains:

 

C8 Edge HD

ZWO 294 MC Pro, binned 2 x 2 (seeing did not permit usage at 1 x 1)

Exposures: 2 seconds and 5 seconds

Gains:  450 and 570 (max camera can do)

Sharpcap Pro

No darks or flats (i need to generate some darks at 2 x 2 binning)

Duration:  Roughly 10 mins

 

While the 294 is not a good fit for RASA 8, it seems to work well with my C8's.   Especially given the noise level is really low, I can turn up the gain very high.  So wanted to compare a couple of short exposures.

 

 

First here is 

 

exposure = 2 seconds, gain = 570.  I kept the color saturation as low as possible to showcase the details a bit more.

Attached Thumbnails

  • crab_2s_570.png

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#2 SanjeevJoshi

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Posted 21 January 2021 - 03:02 AM

exposure = 2 seconds, gain = 450.  Unfortunately I was a bit more aggressive on the color saturation, but you can still see the difference from gain = 570.

 

 

Attached Thumbnails

  • crab_2s_450.png

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#3 SanjeevJoshi

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Posted 21 January 2021 - 03:03 AM

Exposure = 5 seconds, gain = 450.

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  • crab_5s_450.png

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#4 SanjeevJoshi

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Posted 21 January 2021 - 03:04 AM

And finally, exposure = 5 seconds, gain = 570 (max for camera).

 

 

Attached Thumbnails

  • crab_5s_570.png

Edited by SanjeevJoshi, 21 January 2021 - 03:05 AM.

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#5 SanjeevJoshi

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Posted 21 January 2021 - 03:10 AM

I think 5S x gain 450 may be a tad better than 2S x 570 but its pretty close.   Which one do you think is the best?

 

Overall, I am impressed with what either can do.   Especially with 2S x 570, it opens up the potential to get a pretty close view in about 5 mins - although 8 to 10 mins seems to be ideal.

 

Using high gain with a camera like 294 may be a saving grace for slow systems in EAA.

 

Ignore the bands, they are a result of vignetting and weather.



#6 mehdymo

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Posted 21 January 2021 - 04:24 AM

Very interesting. Thanks for sharing.



#7 GaryShaw

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Posted 21 January 2021 - 09:05 AM

Hi
What makes you say the 294 is a bad match for the rasa?

Thank you for providing the experimentation above.

Gary



#8 SanjeevJoshi

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Posted 21 January 2021 - 09:51 AM

Hi
What makes you say the 294 is a bad match for the rasa?

Thank you for providing the experimentation above.

Gary

294 under samples, specifically for RASA 8, and that’s on average seeing.  Worse with good seeing (prohibitive).   I would guess the same for any other C8 F2 system.

 

So while I love it for fitting and framing the largest DSO’s, a 183 (I own) or 533 (based on others) beats the pants off 294 wrt image quality / details.   Zooming, forget that.  

 

I therefore use it for the really widefield (70 arc minutes plus) on RASA 8, and with native C8 F10.

 

With the 183, I can frame up to 70 arc minutes on RASA 8, and it works great for most seeing conditions.  I can also zoom into to see M1, and it’s a reasonable quality for a 5 arc minute object.  Just based on specs, 183 with the quality it provides is likely the best today for RASA 8 for versatility, 533 offers a different trade off with larger pixels and a square FoV.

 

There does not appear to be a camera that can work well with RASA 8 in excellent seeing (like a few times a year) to zoom in.  RASA 8 seems to need an even smaller pixel, big sensor with a deep enough well.   I don’t think most people are going to miss this much.


Edited by SanjeevJoshi, 21 January 2021 - 10:05 AM.

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#9 Borodog

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Posted 21 January 2021 - 10:10 AM

Were you guiding or just tracking?

Sadly I think I have too much plain old vibration to shoot even 2s with my F/10 C8. It’s fine for planetary or lunar because of the ultra short exposure times, but looks like hell for DSO.

#10 Borodog

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Posted 21 January 2021 - 10:14 AM

Also the RASA is so fast I think your best bet might be mosaics with a smaller sensor/pixel camera. I’m not sure well depth matters too much; just stack more frames.

Edited by Borodog, 21 January 2021 - 10:14 AM.


#11 SanjeevJoshi

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Posted 21 January 2021 - 10:16 AM

Were you guiding or just tracking?

Sadly I think I have too much plain old vibration to shoot even 2s with my F/10 C8. It’s fine for planetary or lunar because of the ultra short exposure times, but looks like hell for DSO.

Just tracking.   View was a bit jumpy just to seeing, scintillating stars.

 

Hmm I was using my AVX but even the Evo mount just do fine, I will need to use a star diagonal and be more careful since it’s a cooled camera, 133 mm back focus.

 

I am pretty sure it’s not a typical limitation for a Evo type mount.   Is yours old?


Edited by SanjeevJoshi, 21 January 2021 - 10:20 AM.

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#12 SanjeevJoshi

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Posted 21 January 2021 - 10:18 AM

Also the RASA is so fast I think your best bet might be mosaics with a smaller sensor/pixel camera. I’m not sure well depth matters too much; just stack more frames.

Yes, I am too lazy to do mosaics.  I just enjoy it during the session, grab a couple pics if anything is worth saving.   I don’t have any processing programs.  Just good old Microsoft to crop and resize to fit the forum requirements.


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#13 GaryShaw

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Posted 21 January 2021 - 05:45 PM

Luckily the RASA 11” that I’ve also been eye-ing does ok with the 294 from ‘very poor’ through ‘ok’ seeing. It even looks like it can push a bit into the ‘good’ range of seeing..... seldom experienced at my primary observing site anyway. 
 

I’ve been wavering between the a RASA 8” versus 11” so perhaps this pushes me a bit towards the 11” although there are other factors that play into it besides my love of the 294. Thanks for making the comment Sanjeev.

Gary



#14 SanjeevJoshi

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Posted 21 January 2021 - 05:57 PM

Luckily the RASA 11” that I’ve also been eye-ing does ok with the 294 from ‘very poor’ through ‘ok’ seeing. It even looks like it can push a bit into the ‘good’ range of seeing..... seldom experienced at my primary observing site anyway. 
 

I’ve been wavering between the a RASA 8” versus 11” so perhaps this pushes me a bit towards the 11” although there are other factors that play into it besides my love of the 294. Thanks for making the comment Sanjeev.

Gary

I love my RASA 8 no question.  But this is also true.  A RASA is such a worthy bucket list item, someday my dream would be to own a 11 or better yet a 14 on a fixed pier in my backyard.   Just switch a camera occasionally if needed, otherwise own the skies!   Without the specific experience of owning one, I would say 11 or 14 if I had a choice :)

 

in my case a long term move is inevitable, and I will need to start thinking of a more permanent system once I settle down.  Until then, it’s ridiculously easy to carry out the AVX and the RASA 8 does great with it.

 

Yes 294 should do much better with those.   I love the 294 and as you can see - even at max gain, the performance is great.


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#15 donstim

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Posted 21 January 2021 - 06:57 PM

Using such high gain values sacrifices a lot of dynamic range. On a mostly bright object and especially for EAA that should be an okay tradeoff for capture time as you have shown.


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#16 SanjeevJoshi

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Posted 21 January 2021 - 07:37 PM

Using such high gain values sacrifices a lot of dynamic range. On a mostly bright object and especially for EAA that should be an okay tradeoff for capture time as you have shown.

I agree.  Since I am looking at images captured in a few mins just for the sake of viewing and an observation log or a forum post, the quality is plenty good for me :)

 

Using 2 second exposures at high gain opens up the ability to use F10 at native resolution with shorter windows of time.

 

I am picking on M1 for a specific reason.  I continue to test M1 under varying conditions, OTA's, cameras, set ups.. its not an incredibly tough target but it is not a slam dunk like many others.   Seeing conditions, set ups will impact the views, so if I can get a EAA quality view thats comparable, mission accomplished!


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#17 Borodog

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Posted 21 January 2021 - 11:22 PM

Just tracking.   View was a bit jumpy just to seeing, scintillating stars.

 

Hmm I was using my AVX but even the Evo mount just do fine, I will need to use a star diagonal and be more careful since it’s a cooled camera, 133 mm back focus.

 

I am pretty sure it’s not a typical limitation for a Evo type mount.   Is yours old?

Heh. My C8 is a 1985 Celestron-Byers Worm Gear Drive on an old Meade wedge on an even older C14 tripod.

 

Yes, I am too lazy to do mosaics.  I just enjoy it during the session, grab a couple pics if anything is worth saving.   I don’t have any processing programs.  Just good old Microsoft to crop and resize to fit the forum requirements.

 

You say that because you haven't tried Microsoft ICE (Image Composite Editor I think). Drag in images, click Next a couple times, nearly perfect mosaic every time. The image in this thread was nearly 30 individual tiles mosaiced in ICE with I think 2 clicks:

 

https://www.cloudyni...x#entry10772243

 

The original full size image is 33 Mpxl, FYI.


Edited by Borodog, 21 January 2021 - 11:24 PM.

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#18 DSO_Viewer

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Posted 22 January 2021 - 12:20 AM

Yes, I am too lazy to do mosaics.  I just enjoy it during the session, grab a couple pics if anything is worth saving.   I don’t have any processing programs.  Just good old Microsoft to crop and resize to fit the forum requirements.

How would you do mosaics anyways for EAA?

 

Steve



#19 DSO_Viewer

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Posted 22 January 2021 - 12:23 AM

Looking at your results definitely shows more sharpness and better contrast in the lower gain.

 

Steve




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