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First Quarter Moon, April 2019

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#1 Tom Glenn

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Posted 25 May 2019 - 02:25 AM

I took this image on April 12, 2019 (local time), but didn't finish working on it until now due to a general lack of time.  Conditions were overall poor, and at the limit of where I even bother capturing data and processing it, but the outcome was acceptable.  As has been discussed in many other threads recently, this would be "good" seeing for many people.  So the terms are basically meaningless.  In order to get the highest quality images you need conditions that many people never witness.  This was taken the day before my previous lunar post, which was captured under better conditions (and therefore processed sooner since I was more excited about it).  The capture details are basically the same as was discussed at length in the other thread.  C9.25 Edge HD, ASI183mm, green filter.  The first link goes directly to the full sized image.

 

https://live.staticf...8d6e473cb_o.png

 

 

47927848556_d6c348e8e1_b.jpgFirst Quarter Moon, April 2019 by Tom Glenn, on Flickr


Edited by Tom Glenn, 25 May 2019 - 03:03 AM.

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#2 havasman

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Posted 25 May 2019 - 02:43 AM

Very fine!



#3 Foc

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Posted 25 May 2019 - 02:47 AM

I would call that very acceptable, indeed a classy result.

 

As you say the general use of 'seeing' is highly variable and unlikely to change until such day as our telescopes come standard with some seeing index and bortle estimator.  When that days comes most of us untravelled scopers will then be very disappointed with the readouts.



#4 DMach

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Posted 25 May 2019 - 03:28 AM

Acceptable indeed! :)

#5 aeroman4907

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Posted 25 May 2019 - 03:58 PM

Hi Tom,

 

I know it is not quite a resolute as you would like, but it still is a very nice image and is worth keeping, particularly since libration keeps things interesting.



#6 Tom Glenn

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Posted 25 May 2019 - 04:16 PM

Thanks to all for the comments.  I'm actually pleased with the outcome, provided that it is viewed at an appropriate scale.  If the full image is viewed at the equivalent of a 300 dpi print scale, in which the entire image would be 35 inches tall, then it looks fantastic.  Only when attempting to pixel peep farther than that does it not quite meet expectations, although admittedly, those expectations are high.  



#7 Tom Glenn

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Posted 25 May 2019 - 04:40 PM

..... worth keeping, particularly since libration keeps things interesting.

Very true regarding libration.  For an interesting comparison of the dramatic difference at identical phases, look at this First Quarter Moon that I posted last year.

 

https://flic.kr/p/29vx4t4

 

The Moon in that post was 53% illuminated, whereas the one in this post is 54% illuminated.  So basically identical phase.  However, there is a dramatic difference in the features that are along the terminator.  In this image I have presented here, Vallis Alpes is already completely illuminated, the sun is rising on the rim of Plato, Montes Apenninus are illuminated all the way to the edge of Eratosthenes, and Ptolemaeus, Alphonsus and Arzachel are completely illuminated, and the sun is rising on Rupes Recta.  In the image from last year, the sun has not even begun to rise on a number of these features, with the terminator still well to the East, despite the fact that the fraction illuminated is the same.  The sub-Earth location in the 2018 image was 7.5E, whereas in the 2019 image above it was -4.4W.  The equates to a ~12 degree difference in the longitude of the terminator, which is very obvious in the comparison.  Also note the difference in proximity of Mare Crisium to the limb.  

 

Also, going back and looking at the old image myself, I will need to go back and "correct" a few things, if I have time (which I probably won't!).  I must have liked that version at the time, but looking at it now, I would choose to make the image brighter, especially towards the eastern limb.  And the maria are too dark imo (entire image needs a slight gamma or curves adjustment), but that's just a self critique nearly a year later!


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#8 DesertRat

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Posted 25 May 2019 - 08:01 PM

Tom,
You did it again with this splendid image! bow.gif

 

Its remarkable in that details are preserved on the bright limb as well as the terminator.  And there are so many of those details.  Its just beautiful!

 

Are you capturing in > 8 bit mode?  The reason I ask is I found this was needed in order to capture simultaneous details in both disk and prominences in solar imaging.

 

Glenn



#9 Tom Glenn

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Posted 26 May 2019 - 12:59 AM

Tom,
You did it again with this splendid image! bow.gif

 

Its remarkable in that details are preserved on the bright limb as well as the terminator.  And there are so many of those details.  Its just beautiful!

 

Are you capturing in > 8 bit mode?  The reason I ask is I found this was needed in order to capture simultaneous details in both disk and prominences in solar imaging.

 

Glenn

Thanks for the nice comments, Glenn.  I have one more image to process to complete a trilogy spanning April 12-14, but time has been in limited supply.  Actually, this image was taken in 8 bit mode.  I do have a number of thoughts on this matter as it relates to lunar imaging, based upon many hundreds of hours of imaging and processing in the past few years.  In a frame for frame matchup, say by stacking an equal number of 8 bit and 12 bit frames (most cameras are limited at 12 bits, some at 14, when capturing in "16" bit mode), the 16 bit files always allow you to push the shadow detail more in lunar images.  No doubt about it.  But in anything less than very good seeing, the differences are limited and manageable.  

 

Emil made a post a number of years ago, long before I joined CN, and I see that you have commented on that thread.  I have always enjoyed reading that post as a reference about how noise affects bit depth, although it is really more focused on planetary imaging, where the dynamic range is very limited to begin with.  With the accessibility of larger frame cameras with small pixels, that can achieve high resolution on the Moon while spanning a huge dynamic range, this topic should really be revisited.  I have done some tests with data that I have captured in 12 bits and then downsampled to 8 bits using PIPP, and then run side by side comparisons.  I have never posted the results because, quite frankly, it takes a lot of time to get a post like that together, but it is very clear that shadow detail can be pushed further with less noise in the 12 bit stacks than with 8, even when stacking 1000 frames.  I believe the only legitimate way to test this is to downsample the 12 bit file, because otherwise you cannot control for the seeing variability from capture to capture.  Perhaps eventually I will post those results.  But the basic summary is that there is more quantization error at the very edge of the terminator in the 8 bit stack compared to the 12, which necessitates more moderation in processing for the 8 bit file.  However, the real world impact is not that great, because there is generally no reason to push the shadows to the extreme in every instance.  

 

That being said, I have found that when capturing lunar images in 8 bits, if you stack 1000 frames, you get a very acceptable result even when pushing shadow detail.  If file size and frame rates were not issues, I would always capture in 12+ bits for the Moon.  But in the case of the image presented in this post, I could tell immediately upon looking at the live view window that the seeing was relatively poor, and I was going to need to be very selective with my frames.  So I captured 5000 frames per file, and stacked 1000.  I initially thought I might have to stack even less, but the 1000 frame stack looked pretty good.  In situations like this, any benefit in dynamic range that a 12 bit capture may offer is negated by the inability to capture as many frames to combat the seeing.  Each 5000 frame file here is already 100GB in size, and this would become 200GB in 12 bits, at a slower frame rate.  When seeing is better, I do like to capture in 12 bits, although recently I haven't had those conditions.  Hard drive space and processing also become limiting technical issues.  Huge files are a pain in many respects.  

 

My thoughts about lunar processing have evolved over the past several years.  I'd like to think I keep improving, and looking back at some old images, I think this is the case.  In general, my goal is to achieve something that looks like a natural view of the Moon.  In many respects, the Moon is an easy standard, because we can all look up and see what it looks like.  Yet one would be surprised how many lunar images simply don't look like the Moon.  Oversharpening is one common problem, but even if we overlook that issue, the main difficulty with lunar images is creating a balanced image that matches the tonality that we see by eye.  The raw images that come from the camera generally do not faithfully capture the tonal distribution that we see by eye.  Achieving this typically requires many subtle adjustments to the tone curve in Photoshop, completely independent of any sharpening.  In my opinion, the resolution of a lunar image is almost irrelevant, because even low resolution images can be displayed at an appropriate scale so as to look suitable.  However, an unnatural tonal distribution is immediately apparent, no matter the image scale, because we all know what the Moon looks like.

 

One final element to this puzzle is the variability in displays, coupled with the adaptation of the human eye.  I found this out in many of my earlier postings, in which I would look back at an image the next day after posting and see that it looks dark.  I discovered that I frequently process images and post at night (this hobby is nocturnal after all, but also I have my free time at night).  At night, with low level interior lighting and adapted vision, what looks good on the monitor will often look very dark when viewed in daylight conditions.  I wasn't paying enough attention to the final histogram.  I always process my final images by eye, and purely subjective assessment, rather than by any formula, but I do use the histogram to guide some of the decisions.  I try to find a region of the Moon that should probably register as "middle gray", and make sure this is reflected in the histogram by spot checking the region in Photoshop.  This is all completely subjective, as is the concept of middle gray itself, but it is worth noting than an 18% gray card, as pioneered by Ansel Adams as representing a neutral gray, registers at about a tone value of 124 (on a 0-255 scale) in sRGB color space (although I have seen values as low as 117 reported).  This can be a useful reference when spot checking an image.  In the case of the image presented in this post, I increased the highlights at the very last minute because I felt like my penultimate version was coming out somewhat muted along the limb, and not reflective of what the Moon looks like.  But ultimately, a lot of this is purely subjective.  


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