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A Closer Look At NightCap Controls

astrophotography EAA imaging NV
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#1 Jeff Morgan

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Posted 22 October 2019 - 07:15 PM

NV Phonetography has come a long way, and if you have not seen them check out GeezerGazer’s recent thread which features the best results I have seen to date:

 

https://www.cloudyni...aphy/?p=9700859

 

These results have inspired me to redouble my own efforts. (And get a new phone, mine is now two models out of date!) Old phone and cheesy adapter aside I feel I have not been using NightCap effectively, overexposing most targets. So last night I systematically shot a panel of photos to share, looking at each NightCap setting individually.

 

The target was Cederblad 214 (aka Sharpless 2-171) a very bright nebula in Cepheus. Nothing special about that target selection. It is a detailed target with bright areas, a tiny cluster, dark lanes and features.

 

The scope used is a Takahashi Epsilon e180, 180mm aperture working at f/2.8. My NVD is the Mod 3C with L3 intensifier (white). I was working at prime focus.

 

One of the variables I have been obsessing about was gain setting on the NVD. However, I noticed something when I attempted to focus using a zoomed view on the iPhone screen: the phone adds it own scintillation! Based on that I made the decision to turn NVD gain to Full and let the NightCap software average it out.

 

Likewise, to minimize variables I used a 7nm filter, 1/3 second exposures (iPhone X max setting), 20 second averaging runs, and held ISO to 3200 in the early frames (ISO Boost = LOW to enable 3200 speed). Changes from that protocol will be noted as different parameters are compared in later posts.

 

Let’s dive in ...


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#2 Jeff Morgan

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Posted 22 October 2019 - 07:17 PM

Under the Settings menu in NightCap the first control I examined was Light Boost. It is a slider control, no numerical value given. The Grain Reduction was set to Off in these three frames.

 

  • Trial 1: Light Boost Off
  • Trial 2: Light Boost Mid
  • Trial 3: Light Boost Full

 

Lesson Learned: Light Boost + High ISO = Bad.

 

However, Light Boost will make a return later ...

Attached Thumbnails

  • Trial 1 LB Off Grain off.jpg
  • Trial 2 LB mid Grain off.jpg
  • Trial 3 LB full Grain off.jpg


#3 Jeff Morgan

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Posted 22 October 2019 - 07:20 PM

Next control to examine is Grain Reduction. Also a slider control. In this series, Light Boost was off, allowing me to re-use Trial 1 photo.

 

  • Trial 1: Grain Reduction Off
  • Trial 4: Grain Reduction Mid
  • Trial 5: Grain Reduction Full

 

If you are not seeing a big reduction between the Mid and Full settings, don’t feel bad. Looking at the 5 mb TIFFs on my computer screen I see very little difference either.

 

Lesson Learned: Grain Reduction set to Mid at a minimum. Leaving it on Full is probably advisable since this is a Device adjustment, not a Subject adjustment. NVD’s and cell phone cameras are both capable of scintillation.

Attached Thumbnails

  • Trial 1 LB Off Grain off.jpg
  • Trial 4 LB off Grain mid.jpg
  • Trial 5 LB off Grain Full.jpg


#4 Jeff Morgan

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Posted 22 October 2019 - 07:22 PM

Less grainy photos are always desirable, and GeezerGazer’s work shows I have much room for improvement. One way of attacking this is through a lower ISO setting. Of course this makes the sensor less sensitive, instinct says longer exposures will compensate. So this next panel shot at ISO 1600 examines that.

 

From here on out, the ISO Boost feature of NightCap is OFF.

 

  • Trial 6: 20 second sampling run
  • Trial 7: 30 second sampling run
  • Trial 8: 40 second sampling run

 

Don’t see much difference? Again, looking at the full-res TIFFs neither do I. And herein is a subtlety of NightCap. It is Averaging, not Stacking as in traditional astro-imaging.

 

Lesson Learned: The camera’s single frame exposure limit is controlling.

 

Bonus Lesson: Field Rotation happens at very short time scales!

 

Stepping through the exposures (and particularly this set) Field Rotation was quite noticeable. If you download these thread photos in sequence and rapidly step through them it will jump out at you. This entire sequence of 26 images only took 17 minutes to shoot. I can even see it in short frames shot back-to-back! My TTS Panther mount does have a de-rotator which I was not using (next time I will be). For those using a driven alt-az mount, consider keeping sampling runs under 20 seconds.

Attached Thumbnails

  • Trial 6 Same as 5, ISO 1600 20 secs.jpg
  • Trial 7 Same as 6, ISO 1600 30 secs.jpg
  • Trial 8 Same as 7, ISO 1600 40 secs.jpg


#5 Jeff Morgan

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Posted 22 October 2019 - 07:24 PM

Building on the last post, I ran a series of panels using identical to the previous eight trials, only with a lesser exposure setting. 1/4 second vs. 1/3 second. A small difference, but I wanted to see if the pixels showed signs of a saturation point. I think the imagers refer to this as a full-well condition. In hindsight I could have ran this particular experiment better using many exposure times. But that thought was a bit late and will have to wait for another night, here is what I have now:

 

  • Trial 1: 1/3 second
  • Trial 9: 1/4 second

Attached Thumbnails

  • Trial 1 LB Off Grain off.jpg
  • Trial 9 same as Trial 1, shorter exposure.jpg

Edited by Jeff Morgan, 22 October 2019 - 07:25 PM.


#6 Jeff Morgan

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Posted 22 October 2019 - 07:24 PM

  • Trial 2: 1/3 second
  • Trial 10: 1/4 second

Attached Thumbnails

  • Trial 2 LB mid Grain off.jpg
  • Trial 10 same as Trial 2, shorter exposure.jpg

Edited by Jeff Morgan, 22 October 2019 - 07:26 PM.


#7 Jeff Morgan

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Posted 22 October 2019 - 07:27 PM

  • Trial 3: 1/3 second
  • Trial 11: 1/4 second

Attached Thumbnails

  • Trial 3 LB full Grain off.jpg
  • Trial 11 same as Trial 3, shorter exposure.jpg


#8 Jeff Morgan

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Posted 22 October 2019 - 07:28 PM

  • Trial 4: 1/3 second
  • Trial 12: 1/4 second

Attached Thumbnails

  • Trial 4 LB off Grain mid.jpg
  • Trial 12 same as Trial 4, shorter exposure.jpg


#9 Jeff Morgan

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Posted 22 October 2019 - 07:29 PM

  • Trial 5: 1/3 second
  • Trial 13: 1/4 second

Attached Thumbnails

  • Trial 5 LB off Grain Full.jpg
  • Trial 13 same as Trial 5, shorter exposure.jpg


#10 Jeff Morgan

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Posted 22 October 2019 - 07:30 PM

  • Trial 6: 1/3 second
  • Trial 14: 1/4 second

Attached Thumbnails

  • Trial 6 Same as 5, ISO 1600 20 secs.jpg
  • Trial 14 same as Trial 6, shorter exposure.jpg


#11 Jeff Morgan

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Posted 22 October 2019 - 07:31 PM

  • Trial 7: 1/3 second
  • Trial 15: 1/4 second

Attached Thumbnails

  • Trial 7 Same as 6, ISO 1600 30 secs.jpg
  • Trial 15 same as Trial 7, shorter exposure.jpg


#12 Jeff Morgan

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Posted 22 October 2019 - 07:32 PM

And finally ...

 

  • Trial 8: 1/3 second
  • Trial 16: 1/4 second

Attached Thumbnails

  • Trial 8 Same as 7, ISO 1600 40 secs.jpg
  • Trial 16 same as Trial 8, shorter exposure.jpg


#13 Jeff Morgan

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Posted 22 October 2019 - 07:37 PM

In this next series of panels, the Light Boost control makes its comeback! Specifically, I would like to run the lowest ISO possible for the smoothest image.

 

But less ISO = less light. Could Light Boost compensate? You be the judge. Light Boost and Grain Reduction both set to Full as ISO varies, 1/4 second exposures, 20 second averaging.

 

  • Trial 17: ISO 1600
  • Trial 18: ISO 800
  • Trial 19: ISO 400
  • Trial 20: ISO 200
  • Trial 21: ISO 100

 

One of the things years and decades of amateur astronomy has conditioned us to do is seek out the faintest wisps and extents of objects. My bet is to say that most of you immediately liked the ISO 1600 exposure because it shows the faintest outer edges.

 

Yet consider this: shouldn’t the blacks (empty space) be truly black, and not some intermediate shade of gray?Based on that thinking, I am liking the ISO 400 and 200 images quite a bit. Had I swapped the 7nm for a 12nm filter, in my eyes the contest might be between the ISO 200 and ISO 100 images.

 

Lesson Learned: Light Boost feature is very attractive around ISO 800 and below.

Attached Thumbnails

  • Trial 17 LB Full, Grain Full ISO 1600.jpg
  • Trial 18 LB Full, Grain Full ISO 800.jpg
  • Trial 19 LB Full, Grain Full ISO 400.jpg
  • Trial 20 LB Full, Grain Full ISO 200.jpg
  • Trial 21 LB Full, Grain Full ISO 100.jpg


#14 Jeff Morgan

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Posted 22 October 2019 - 07:38 PM

Some of you may have noted the last panel was shot at 1/4 second instead of the 1/3 second exposure my phone is capable of. Yes, I did repeat Trials 17-21 at 1/3 seconds. I’ll pair them up with their corresponding “short” exposures so you can compare:

 

  • Trial 17: 1/4 second
  • Trial 22: 1/3 second

Attached Thumbnails

  • Trial 17 LB Full, Grain Full ISO 1600.jpg
  • Trial 22 Same as 17, longer exposure.jpg


#15 Jeff Morgan

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Posted 22 October 2019 - 07:39 PM

  • Trial 18: 1/4 second
  • Trial 23: 1/3 second

Attached Thumbnails

  • Trial 18 LB Full, Grain Full ISO 800.jpg
  • Trial 23 Same as 18, longer exposure.jpg


#16 Jeff Morgan

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Posted 22 October 2019 - 07:40 PM

  • Trial 19: 1/4 second
  • Trial 24: 1/3 second

Attached Thumbnails

  • Trial 19 LB Full, Grain Full ISO 400.jpg
  • Trial 24 Same as 19, longer exposure.jpg


#17 Jeff Morgan

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Posted 22 October 2019 - 07:41 PM

  • Trial 20: 1/4 second
  • Trial 25: 1/3 second

Attached Thumbnails

  • Trial 20 LB Full, Grain Full ISO 200.jpg
  • Trial 25 Same as 20, longer exposure.jpg


#18 Jeff Morgan

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Posted 22 October 2019 - 07:41 PM

  • Trial 21: 1/4 second
  • Trial 26: 1/3 second

Attached Thumbnails

  • Trial 21 LB Full, Grain Full ISO 100.jpg
  • Trial 26 Same as 21, longer exposure.jpg


#19 Gavster

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Posted 23 October 2019 - 01:27 AM

Great details here Jeff and I like the image comparisons a lot! I like that your images don’t have the blue tint that appears in some phone images.

Nightcap is a great app for iPhone users.

I think some Android phones do have a definite advantage being able to do longer 30 second exposures with low iso for minimal grain and tighter stars. 


Edited by Gavster, 23 October 2019 - 01:32 AM.



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