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First time doing 15 minute subs from the city.

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#26 Astrolamb

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Posted 14 April 2021 - 01:35 PM

Here's your only real mistake.  It's pretty serious.

 

Flats ADU should be _much_ larger than lights ADU.  For example, take the D5300 (yours) and the D5500 (mine, identical for this purpose).

 

Lights ADU should be in the vicinity of 1000 ADU (16 bits), raw.  Bias subtracted, 400 ADU (16bits).  ISO 200.  Getting it exactly at 1000 has no value whatsoever.  The linear histogram is a thin spike on the far left.

 

Flats should be about 32000 ADU (16 bits, which has 64000 as the maximum possible ADU).  The linear histogram should be about in the middle of the graph.  Getting it exactly at 32000 has no value.

 

If you shot flats the same ADU as your lights, it's no wonder your corners were too dark.   I'd expect them to be.

 

Needless to say, the calibration software makes this all work.  BUT, you must include either bias or dark flats.  Or it won't work.

 

Yeah that really was a huge mistake looking back knowing all I do now. 

 

When I opened a really overexposed flat up in Iris it looked like the maximum for a pure white linear frame was ADU: 16383 - Density: 24160256

Everything else was zero.. 

I only downloaded Iris several days ago when started learning about all of this, so I am definitely still learning the software. Would 16383 ADU being the max signify that I am looking at my photo in a linear 14bit depth? 

 

After I tuned the exposure back a bit I got the peak of the histogram on Iris to sit at ~8000 ADU, I figured this was pretty perfect since ~16000 ADU seemed to be the max.

 

I always use bias, but I did not think about making the firm point that bias or dark frames are absolutely necessary when taking exposures like this for everyone else reading. 

 

I am happy to hear that I have a pretty good foundation of the concepts though! I really can't wait to see how big of a difference this will make for me on my next trip out to my local dark site.

 

Did anything change after modification of your D5500? I know you will get to 1000ADU quicker on your light frames after modification but was there anything else that changed? 



#27 Astrolamb

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Posted 14 April 2021 - 01:37 PM

This is a timely thread for me also. I have been shooting this target from a Bortle 6 with a D5300 and no filters (night 3 now in a row)

Nights 1 & 2 are about 2.5 hours of 180s subs at ISO400

On Facebook today I saw someone who got a lot more detail from a similar location with shorter subs

 

Tonight I will capture around 3 hours of 60s subs of the same target and except for the moon being a little different, everything else will be as similar as possible

 

Tomorrow I am going to do some stacking and basic processing and see how things are different

 

I am definitely clipping a LOT fewer pixels tonight (~70 compared to ~900) and my subs are in the 900 ADU range compared to I think around 1500 ADU at 180s

 

It's going to be a super interesting test

 

I can't wait to see the results! you will definitely have to post them up!


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#28 limeyx

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Posted 14 April 2021 - 01:42 PM

Yeah that really was a huge mistake looking back knowing all I do now. 

 

When I opened a really overexposed flat up in Iris it looked like the maximum for a pure white linear frame was ADU: 16383 - Density: 24160256

Everything else was zero.. 

I only downloaded Iris several days ago when started learning about all of this, so I am definitely still learning the software. Would 16383 ADU being the max signify that I am looking at my photo in a linear 14bit depth? 

 

After I tuned the exposure back a bit I got the peak of the histogram on Iris to sit at ~8000 ADU, I figured this was pretty perfect since ~16000 ADU seemed to be the max.

 

I always use bias, but I did not think about making the firm point that bias or dark frames are absolutely necessary when taking exposures like this for everyone else reading. 

 

I am happy to hear that I have a pretty good foundation of the concepts though! I really can't wait to see how big of a difference this will make for me on my next trip out to my local dark site.

 

Did anything change after modification of your D5500? I know you will get to 1000ADU quicker on your light frames after modification but was there anything else that changed? 

Yeah for the D5300, 16384 (I think) is the max. I shoot for 6500-9000 ADU in Iris or in PixInsight (statistics set to 16 bit mode)

 

I have been dimming my flat panel to where that takes around 2-3 seconds exposure to get to (I am no longer certain this part is needed but it's working and I am going to stick with it)


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#29 limeyx

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Posted 14 April 2021 - 01:45 PM

I can't wait to see the results! you will definitely have to post them up!

Definitely. I have around 100 180s subs and 200 60s subs so far and expect to image tonight and tomorrow (sub time TBD - 60/120 or 180 - depending on the results of 60)

 

I did notice my eccentricity was higher with the 60s subs (around 0.1 higher) but

- I have a Skyguider Pro so its crapshoot corrall usually

- The moon was a little bigger (but still not really out)

- It's getting a couple of degrees warmer every night

- My PA seemed a little less good 

 

I did do a single 180s shot and the eccentricity was actually better than the 60s - maybe because there was more signal ?

I did notice once I got a ways past the meridian (no flips here, so I just go as far as I can), the sub quality went up briefly but the final 30 or so mins seemed like a very weak signal


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#30 Astrolamb

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Posted 14 April 2021 - 02:12 PM

Definitely. I have around 100 180s subs and 200 60s subs so far and expect to image tonight and tomorrow (sub time TBD - 60/120 or 180 - depending on the results of 60)

 

I did notice my eccentricity was higher with the 60s subs (around 0.1 higher) but

- I have a Skyguider Pro so its crapshoot corrall usually

- The moon was a little bigger (but still not really out)

- It's getting a couple of degrees warmer every night

- My PA seemed a little less good 

 

I did do a single 180s shot and the eccentricity was actually better than the 60s - maybe because there was more signal ?

I did notice once I got a ways past the meridian (no flips here, so I just go as far as I can), the sub quality went up briefly but the final 30 or so mins seemed like a very weak signal

 

When you say eccentricity, what are you referring it to here? The technical side of signal is still such a new topic to me eccentricity is just going over my head at the moment..  I'm just not sure if it refers to guiding accuracy, average ADU signal in frames, or something else entirely.



#31 limeyx

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Posted 14 April 2021 - 02:29 PM

When you say eccentricity, what are you referring it to here? The technical side of signal is still such a new topic to me eccentricity is just going over my head at the moment..  I'm just not sure if it refers to guiding accuracy, average ADU signal in frames, or something else entirely.

Pixinsights measure of star eccentricity in the FWHMEccentricity script. I've found I can have good HFR measures in NINA but poor stars, so I look at NINA first, then measure eccentricity

 

Basically a measure of star roundness/elongation (I am far from an expert here honestly, I just noticed that it was a really good "something is really wrong here" measurement)


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#32 Astrolamb

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Posted 14 April 2021 - 02:47 PM

Pixinsights measure of star eccentricity in the FWHMEccentricity script. I've found I can have good HFR measures in NINA but poor stars, so I look at NINA first, then measure eccentricity

 

Basically a measure of star roundness/elongation (I am far from an expert here honestly, I just noticed that it was a really good "something is really wrong here" measurement)

That right there makes total sense! I have seen it referenced before on here and I believe I have seen it on the sub scores within DSS as well. 

 

Thank you for the clarification!


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#33 calypsob

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Posted 14 April 2021 - 06:04 PM

So the Owl Nebula has been the center object for imaging for a couple of days.

It's a very faint nebula and requires a lot of exposure time when using small telescopes.

I captured some 480sec subs yesterday but the final result was not satisfying.

Today I am doing 15 minute subs through the L-eNhance filter under the Bortle class 8 skies.

Nikon D5300, ISO 800.

I was really surprised to see the amount of detail in one sub.

Here is a quickly stretched 15 min JPEG image, cropped about 30%.

 

attachicon.gifSingle__0006_ISO800_900s__NA.jpg

IMO the dynamic range looks fine, show us the stack. 


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#34 limeyx

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Posted 14 April 2021 - 06:59 PM

That right there makes total sense! I have seen it referenced before on here and I believe I have seen it on the sub scores within DSS as well. 

 

Thank you for the clarification!

I've stacked the 60s lights but unfortunately had some moving dust in the flats, so I am re-doing with yesterdays flats.

 

Its interesting as the end result does not look significantly better or worse than the longer subs, although I did not do any processing at all.

 

I threw away two of the 60s subs due to eggy stars and 1-4 of the 180s subs from each day, so it's also not like the shorter subs are giving me more keepers either.

 

I feel like there may be a bit more red and a bit less light pollution showing in the shorter subs but not yet sure how to quantify this beyond "eying it in"



#35 calypsob

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Posted 14 April 2021 - 07:49 PM

Thank you, your feedback is always appreciated. 

Interestingly enough, the histogram was sitting at 1/3 in a 15 min sub.

I know that for my camera and the equipment the best exposure time to keep the star colors  is around 60sec-120sec.

But, my 4+ hour stack of 480sec subs did not reveal enough fainter details in the outskirts of the nebula. 

It's interesting to see that a single 15min sub showed some good detail.

Not arguing about the best exposure time considering the camera I used, but for the sake of getting more detail, the winner is the 15min sub.

Bob's insight is indeed one method of procuring good data but it is certainly not the only way to capture the entire dynamic range.  It appears to me that you have a good deal of color in the stars with this one sub exposure, the stack may reveal even more. Fine tuning image integration  is more about process optimization, how to use the least amount of resources and achieve the same high quality objective. 


Edited by calypsob, 14 April 2021 - 07:54 PM.

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#36 bobzeq25

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Posted 16 April 2021 - 12:02 PM

Yeah that really was a huge mistake looking back knowing all I do now. 

 

When I opened a really overexposed flat up in Iris it looked like the maximum for a pure white linear frame was ADU: 16383 - Density: 24160256

Everything else was zero.. 

I only downloaded Iris several days ago when started learning about all of this, so I am definitely still learning the software. Would 16383 ADU being the max signify that I am looking at my photo in a linear 14bit depth? 

 

After I tuned the exposure back a bit I got the peak of the histogram on Iris to sit at ~8000 ADU, I figured this was pretty perfect since ~16000 ADU seemed to be the max.

 

I always use bias, but I did not think about making the firm point that bias or dark frames are absolutely necessary when taking exposures like this for everyone else reading. 

 

I am happy to hear that I have a pretty good foundation of the concepts though! I really can't wait to see how big of a difference this will make for me on my next trip out to my local dark site.

 

Did anything change after modification of your D5500? I know you will get to 1000ADU quicker on your light frames after modification but was there anything else that changed? 

Nothing changed, because...

 

I never used it unmodified.  In some sense, it didn't exist.  I bought it online, had it shipped directly to LifePixel for Ha modification.

 

But, modding really doesn't change much except Ha sensitivity and unprocessed color balance, which you fix using routine methods in processing.


Edited by bobzeq25, 16 April 2021 - 04:02 PM.

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#37 limeyx

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Posted 21 April 2021 - 07:10 PM

I can't wait to see the results! you will definitely have to post them up!

Results (Hopefully not hijacking the thread)

 

201 subs at 60 seconds and stacked with CFA drizzle=1

https://drive.google...iew?usp=sharing

 

56 subs at 180s stacked the same way

https://drive.google...iew?usp=sharing

 

Screen capture of a single uncalibrated sub (180s on left, 60s on right). just stretched in PI and screen catured

 

 

Attached Thumbnails

  • 180-60-Sub.JPG

Edited by limeyx, 21 April 2021 - 07:12 PM.

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