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FORUMS Photo Sharing & Visual Enjoyment Astronomy & Celestial 
Thread started 31 Dec 2009 (Thursday) 21:07
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The Official Shoot the Moon Thread

 
LV ­ Moose
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Post edited 7 months ago by LV Moose.
     
Dec 09, 2017 23:09 |  #4726

navydoc wrote in post #18513862 (external link)
I'm sure there are experts out there that can give you a better answer than I can but I think partly, stacking helps overcome atmospheric distortion. This very short video I made recently in 4k shows how the moon shimmers due to heat distortion.

Yeah, I get the heat distortion thing, but how would stacking images help that? For grins, let's say you stack four different images at various opacity, each is "wavy" but in different ways; seem like the final image would be more blurry than any of the single shots; you don't really notice the waves, unless it's shot in a video like the one you posted.

Must be another reason for the stacking.

Orrr...

I could just be stupid. ;-)a


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navydoc
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Dec 09, 2017 23:29 |  #4727

LV Moose wrote in post #18514456 (external link)
Yeah, I get the heat distortion thing, but how would stacking images help that? For grins, let's say you stack four different images at various opacity, each is "wavy" but in different ways; seem like the final image would be more blurry than any of the single shots; you don't really notice the waves, unless it's shot in a video like the one you posted.

Must be another reason for the stacking.

Orrr...

I could just be stupid. ;-)a

From what I understand, stacking takes the sharpest areas of each exposure and blends them into one image that is sharper overall. Some stacking programs use video frames for stacks which can result in hundreds of frames being analyzed and stacked.


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LV ­ Moose
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Dec 10, 2017 01:04 |  #4728

navydoc wrote in post #18514464 (external link)
From what I understand, stacking takes the sharpest areas of each exposure and blends them into one image that is sharper overall. Some stacking programs use video frames for stacks which can result in hundreds of frames being analyzed and stacked.

Yeah, my example wasn't well thought-out... it's late. *yawn*


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MalVeauX
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Post edited 7 months ago by MalVeauX. (7 edits in all)
     
Dec 11, 2017 09:23 |  #4729

Stacking does two things: 1) removes random noise; 2) increases signal to noise ratio. Part of stacking is that you can limit what is stacked and how many are stacked for the final result (which is to limit the stack to only the best least blurry captures, and then stack a number of them that equates to a good signal to noise ratio result).

It does not sharpen an image directly.

Stacking 10 images is not worth it usually, other than for noise reduction (which you can do with a single frame, so again, not really worth it). And that's simply because you have to have more frames to stack to really benefit from it. You get 3 times the signal to noise ratio from 10 images, but you get 6 times the signal to noise ratio from 40 images stacked. And you get 10 times the signal to noise from stacking 100 frames. The point of stacking is to again reduce random noise and increase signal to noise ratio, and it has diminishing returns. So stacking somewhere with the idea of getting 5~7 times the signal to noise ratio can be worth it. Less than that, probably not so worth it, not with today's cameras that already have very good dynamic range and low noise.

Stacking for a full disc image is also not really worth it usually (because the magnification is low and the seeing is less apparent with its effects) unless it's actually a mosaic of several images captured at a higher magnification where the seeing is the limiter. Again, it can be useful if your goal is to reduce noise and to be able to stretch the histogram.

Seeing is the great limiter of high magnification for terrestrial based imaging. You cannot change the seeing. You can only attempt to get lucky and get captures when seeing is calm for a moment (beat the seeing). This is why people capture video instead of still images for high magnification images of the moon, surface, planets, sun, etc.

Stacking 500~1,000 images can be worth it. But only if you limit it to a few frames that are best so that the stacking doesn't result in a softer overall result. So for example, it's common to grab 500 frames (video) of the moon at high magnification to beat the seeing, and stack a small percentage of the best frames (30~40 is a good choice as a starting point for the lunar surface, too many will soften the image due to including more tolerance for more blurry captures). What that means, is you're capturing a lot of frames to perform lucky imaging to potentially grab a moment when the seeing is as good as it can be at the moment (which is fleeting moment). Then, instead of stacking all the frames, you limit it to only stacking the best frames which have the best seeing (which basically means having the least blur). The resulting image will be virtually noise free and have a higher signal to noise ratio so that you can manipulate the histogram better. It does not create a sharper image from stacking. It simply removes the blurry images (limit) so that the images you are stacking are the better quality ones with less blur (so they will look sharper). The increase in signal to noise ratio from stacking is only useful if you're processing it (such as stretching the histogram to lift shadows and pull detail from dark or high contrast areas on the surface, without clipping highlights).

+++++++++++++++

An example of using the lucky imaging to create a high resolution full lunar disc image from high magnification smaller images to make a mosaic:

A) I captured 250 frames per video to create each individual image. I stacked around 40 of those to result in the final image resulting image each time. I did this 6 times so that I had panels to create a mosaic of the full disc out of individual higher resolution panels. Here's an individual panel (click the link and click the image to see it at its full resolution, this is high magnification):

http://astrob.in/28242​5/0/ (external link)

B) Here's the 6 panels stitched together as a single high resolution mosaic of the disc (go to the link, look at the full resolution image by clicking the image and then top right there's an icon for full resolution):

http://astrob.in/28242​4/0/ (external link)

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WestCoastCannuck
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Dec 11, 2017 12:16 |  #4730

MalVeauX wrote in post #18515318 (external link)
Stacking does .......
Very best,

Thanks SO much for jumping in here with an excellent and knowledgeable reply!!

The question had been addressed to me, because I stack fewer images.... and when it works well, I am using sharp low ISO images. In THEORY, and as you so well explained, I should get little benefit. But, I think I do. I may not get much more detail, but a stacked file of 10-15 images shot on a clear night (say 10-15 BEST out of 50 or so) nets me a nicer result when processed with the tools in Astra Image. (deconvolution being the most important) I end up with a cleaner, "deeper" file for lack of a better word. Better IQ. Nicer image.

On poor seeing nights.... no. Too much variation between frames.

When I get time, I will look through my files for a good example comparing - and post.

Very best regards

Mike


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MalVeauX
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Post edited 7 months ago by MalVeauX.
     
Dec 11, 2017 12:46 |  #4731

WestCoastCannuck wrote in post #18515445 (external link)
Thanks SO much for jumping in here with an excellent and knowledgeable reply!!

The question had been addressed to me, because I stack fewer images.... and when it works well, I am using sharp low ISO images. In THEORY, and as you so well explained, I should get little benefit. But, I think I do. I may not get much more detail, but a stacked file of 10-15 images shot on a clear night (say 10-15 BEST out of 50 or so) nets me a nicer result when processed with the tools in Astra Image. (deconvolution being the most important) I end up with a cleaner, "deeper" file for lack of a better word. Better IQ. Nicer image.

On poor seeing nights.... no. Too much variation between frames.

When I get time, I will look through my files for a good example comparing - and post.

Very best regards

Mike

Hi Mike,

What's happening when you stack 10~15 images (or any number) is you're reducing random noise and increasing signal to noise ratio (10 is 3.2 times the signal, 15 is 3.8 times the signal, not much difference). So, because of that, the resulting image will be cleaner (less random noise) which makes it a lot easier to process and sharpen it without it looking messy, noisy, etc (as you will not be sharpening different random patterns of noise) with different sharpening methods. And the reason the file seems deeper, is because of the increased signal to noise ratio which allows you to stretch the histogram so that more of the dynamic range is represented (instead of an all grey looking flat image, you can stretch the histogram and get more contrast without clipping highlights or losing detail in shadows). Having more signal to noise allows more processing latitude. It's just slightly better when stacking 10~15 images compared to a single still image. Is it enough to warrant the extra work involved to capture the images and stack? That's a personal thing. But strictly from a data stand point, it's usually not worth it at that scale compared to the benefits of stacking 4 times that amount or more.

In terms of comparing, be mindful that if you show two different moments in a comparison, you could be simply comparing good seeing to poor seeing in the same few seconds.

For a comparison, I would suggest you show a single frame unstacked from your captures, and then a several-frame-stacked image of the same thing, at 100% crop scale, in two areas: 1) where the deepest shadow is on a group of craters, such as the terminator, with noise, and 2) areas that are relatively smooth and blank such as a mare to see if noise is removed. Ideally use the best still frame to represent the best seeing you captured, compared to stack which will represent variable seeing from several captures. The only difference will be the seeing blur captured, the noise present and the higher potential to stretch the histogram to have more processing latitude.

A lot of times, in general, folk compare a great moon shot and wonder what lens, scope, camera, etc, settings, etc, are used, are really just chasing two things (1) seeing (2) aperture. Seeing is the ultimate limitation of blur. Aperture is the limitation of resolution. Any of us shooting the moon and its details would give everything for the best seeing all the time, rather than the biggest aperture or best equipment.

To show a representation of excellent seeing, here's an example of how really good seeing at near zenith orientation with a small 6 inch aperture allowed me to capture fine detail within a crater, along with craterlets throughout the maria which are normally not seen at all due to blur and low resolution. This is 2,000 frames captured, and 20% of that stacked with excellent seeing conditions.

IMAGE: https://farm1.staticflickr.com/324/31203285930_45293f7171_b.jpg
IMAGE LINK: https://flic.kr/p/PxjZ​Ns  (external link) GassendiCrater_MareHum​orum_12102016 (external link) by Martin Wise (external link), on Flickr

Very best,

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LV ­ Moose
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Post edited 7 months ago by LV Moose.
     
Dec 11, 2017 15:25 |  #4732

MaVeaux, Mike, thanks for responses! I appreciate the time and effort expended. ☺
I remember now hearing of the noise and signal to noise benefits, but it's been a long time.


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Dec 11, 2017 19:08 |  #4733

My understanding is that some astro stacking programs don't just pick the sharpest bits from different frames, but also try to fix geometry distorted by air turbulence (so straight lines look indeed straight and not wavy). Probably not so important for the Moon, but can make a huge difference for planets (Jupiter, Saturn etc.)


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Dec 12, 2017 04:19 |  #4734

I am planning to put the moon and planets into my targets aim for next year, i am still focusing on DSO, but i think the moon is the easy target i can learn at, and i am planning to buy a new camera to be dedicated for the solar system including the moon, not DSO.


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Dec 14, 2017 06:21 |  #4735

Finally i ordered a new camera from ZWO, now i have to wait long until it arrives, and i will put it in use immediately, the moon will be my target with that new camera.

Thanks Martin for your post and example, you are the man!


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Dec 14, 2017 06:38 |  #4736


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A little late, this year's Supermoon.



  
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Dec 14, 2017 22:15 |  #4737

One of my more recent shots still hand held prior to getting a decent tripod shot.

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Ben ­ in ­ San ­ Diego
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Dec 15, 2017 14:54 |  #4738

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IMAGE LINK: https://flic.kr/p/HcQF​wz  (external link) DSC_5291 (external link) by Ben A (external link), on Flickr

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Dec 16, 2017 22:37 |  #4739

Another pre tripod oldy - half moon.

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Post edited 6 months ago by stevieray.
     
Dec 19, 2017 22:46 |  #4740

One day old Moon (0.5% waxing crescent) this evening.

IMAGE: https://farm5.staticflickr.com/4643/39143883502_3d48f7ab93_b.jpg
IMAGE LINK: https://flic.kr/p/22D1​CP9  (external link) 0.5% Waning Crescent Moon (external link) by Steve Christle (external link), on Flickr



  
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