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Stacking moon images. Why?

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#1 Szumi

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Posted 22 September 2019 - 08:03 AM

In another thread I saw a nice picture of the moon.  The technical card indicated that it was made out of 400 frames.  It is big and bright, what is the need for stacking? 

 

Thanks,

 

Szumi



#2 einarin

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Posted 22 September 2019 - 08:11 AM

Earth atmosphere affects all objects in the sky and it spoils the details.

That's why planetary imagers take thousands of frames and use software to pick the best frames and stack them and then you can use wavelets/sharpen routines to make it even sharper/better.

Same applies to moon and sun imaging too.


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#3 TOMDEY

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Posted 22 September 2019 - 08:30 AM

Yep --- the approach is technically justified in the presence of noise of any kind... in this case, the main one being atmospherics scrambling the wavefront. To the extent that our algorithms are able to differentiate object-invariant structure from the atmospheric affectives... one can/should wind up with a better rendition of the object aka the moon looking better.    Tom



#4 RedLionNJ

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Posted 22 September 2019 - 12:30 PM

The moon is indeed big (not a factor) and bright - but not bright enough to be able to capture a single image where the signal-to-noise ratio is really high - to gather enough light, an exposure would have to be in the region of a least an eighth of a second - a lot can happen in such a long time to distort the image formed on the sensor - the camera shutter causes vibration, the Earth rotates, seeing causes other effects, etc.

 

So we take thousands of frames with a shutterless device, each frame being very short, then add them all together with aligning/stacking software. Then we take THAT resulting stack and hope the blurriness can be removed by "scooping up specific amounts of data surrounding each point and moving it back to the point" - all across the image.  This is often called "wavelets" or deconvolution. It's only effective under certain types of seeing.



#5 the Elf

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Posted 25 September 2019 - 02:24 PM

If you want to bring out the subtle color differences in the maria by pumping up saturation you need a stack. If you can live with a monochrome image you can get decent single shots. Using an Ha filter is a good trick. You loose all color of course, but the blurring caused by the atmosphere is less in the red part of the spectrum. Here is an example taken thru a 7nm Baader Ha 1/10s, mono modded T3i:

 

http://www.elf-of-lo...j_Moon2019.html

 

Full moon images often look flat. When sun light comes in with an angle there is high contrast and long shadows at the terminator which makes the image more dramatic.


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#6 Szumi

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Posted 30 September 2019 - 03:59 AM

Thank you for answering my question.  I'll have to give stacking a try some night.  My one shot dslr photo's are not very impressive.


Edited by Szumi, 30 September 2019 - 03:59 AM.



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