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Rosette Nebula - ASI071MC Pro

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#1 ThermalSeeker

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Posted 15 January 2019 - 01:17 PM

This was imaged last Thursday night.  Got off to a late start due to our local astronomy club meeting, but I wanted to try to image with just a UV/IR cut filter from the backyard.  After determining 90s was a decent exposure length without blowing out the cores, I set it up for the night to image with Stellarmate.  After capturing 130 frames through the night, I culled out the bad ones and settled for 94, 90s subs.  This is was my first time imaging without a light pollution filter and I was pleasantly surprised with the results.  As always we all want more integration.  C&C welcomed.  Enjoy!

 

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#2 t-ara-fan

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Posted 15 January 2019 - 06:53 PM

Nice.   I shot it the other night with that camera:  64x 60" subs with my EdgeHD 8 and Hyperstar 4 (f/1.9).

 

I used gain=90, offset=65 using SGP.  I am still working on the processing. 

 

How did you choose the exposure length and gain/offset?  I am still trying different things.


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#3 jgraham

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Posted 15 January 2019 - 07:07 PM

Gorgeous! I love how you processed this showing the nebula's soft colors and detail. Nicely done!


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#4 ThermalSeeker

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Posted 15 January 2019 - 08:32 PM

Nice.   I shot it the other night with that camera:  64x 60" subs with my EdgeHD 8 and Hyperstar 4 (f/1.9).

 

I used gain=90, offset=65 using SGP.  I am still working on the processing. 

 

How did you choose the exposure length and gain/offset?  I am still trying different things.

Thank you.  First off, I chose the gain due to those bright o type stars that seem to want to saturate the sensor quickly, plus this gives me a little extra range in my tones due to increase in dynamic range. (sky background may play in this, im like a bortle 4.5ish to 5 depending on the night.)  Next, offset is always determined by bias histogram, i like my peak around 100 to 200, with no clipping in the black for the entire data.  Then the exposure was easily determined with a few test exposures. I started out with a 120s sub, and realized a lot of my stars were already maxing out the sensor. I reduced it by 10s, until I found 90s was where I needed to be with my f/7 setup.  Measuring star cores and median background values with Pixinsight's readout tool is how I settled on 90s.

 

An offset of 65 seems very high.  At 90 gain, 20 is where I am with the offset on the 071. At 50 gain, 12 is the offset.


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#5 ThermalSeeker

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Posted 15 January 2019 - 08:33 PM

Gorgeous! I love how you processed this showing the nebula's soft colors and detail. Nicely done!

Thanks for the kind words John.



#6 t-ara-fan

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Posted 16 January 2019 - 12:44 AM

 

 

An offset of 65 seems very high.  At 90 gain, 20 is where I am with the offset on the 071. At 50 gain, 12 is the offset.

I got those numbers from the "unity gain" setting in the ZWO driver.

If it is too high, am I correct in understanding that a bias of 65 uses up 0.1% of my 216 dynamic range?



#7 rlsarma

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Posted 16 January 2019 - 01:24 AM

Splendid!! I love your work, Alan. It now encourages me to go for this object once the full moon is over and I'll get a dark sky. But my 9.25 SCT is a problem for getting the whole object to bring inside the frame unless I go for mosaic shots. Let me see.

 

Thanks for sharing your beautiful work.

 

Rajib


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#8 ZL4PLM

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Posted 16 February 2019 - 06:27 PM

I found 65 is way too high and hard to process - I am going to try 20 next run as well - I dont know why its so high the black level means I had to clip it a lot to get processes like ABE to run correctly 



#9 vdb

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Posted 17 February 2019 - 07:13 AM

Offset to high for black levels? I would expect the opposite, the only thing a to high offset has impact on is dynamic range. Setting offset to low for a given gain would mean some pixels will not count all photons ... meaning you get extra noise ... and some background pixels will never reach any value in worst case ...

 

/Yves



#10 ZL4PLM

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Posted 17 February 2019 - 08:09 PM

Offset to high for black levels? I would expect the opposite, the only thing a to high offset has impact on is dynamic range. Setting offset to low for a given gain would mean some pixels will not count all photons ... meaning you get extra noise ... and some background pixels will never reach any value in worst case ...

 

/Yves

 

I suspect Pix ABE etc does not like super bright backgrounds 

 

with offset 65 I found that running ABE left me with an image full of wierd colour artifacts in ABE 

 

First thing I did was look at the histo and theres a huge gap from the left hand edge to where the data starts and a very long slow curve to the side of the lower side bell curves

 

Tweaking the levels at the bottom leads to clipping but ABE then processes correctly 

 

I suspect it does not like very bright backgrounds and needs a lower black level to work 

 

I can't think of anything else as my settings remained the same and the only thing I changed was the left black level and dimmed the image 

 

?? 


Edited by ZL4PLM, 17 February 2019 - 08:11 PM.



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