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Messages - jrista

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991
In case people don't understand "seeing limited", this refers to atmospheric interference when viewing celestial objects like the moon. Twinkle twinkle little star - the star is a point light source to us and should be a non-twinkling dot, but air turbulence, temperature differential, humidity in air all affect (refract) the image of that dot. That's why astrophotographers stack ("average") large numbers of identical moon or planet photos.

Stacking is for reducing noise.  The " lucky imaging technique" where you select the best frames from many (usually from video) is for getting around the seeing limit.  You stack just those best frames to reduce noise on already high resolution images.

It's not an insignificant difference.  In some cases, you can improve from a seeing limited image at 2 arc seconds to a diffraction limited one at better than half an arc second.
Astrophotography seems very complicated - making the results that jrista and others share all the more impressive.

It's pretty complicated, for sure. It should be noted seeing limited spot size is rarely as good as 2" (arcseconds). Because of seeing in Colorado, it's usually somewhere between 3.8-4.1", even worse at times. In most of the US, seeing-limited spot size is usually a little over 3"...if you have a 2" seeing limited spot size, your seeing is pretty good. If you have seeing limited spots that are smaller than 1.5", your seeing is excellent. Assuming you use drizzling to increase the resolution beyond that, if you used full 3x drizzling, resolution could improve to 0.5". With seeing of 3.8", 3x drizzling might be able to improve resolution to 1.3" (you really need a LOT of frames to achieve that, though).

Also, getting diffraction-limited images at less than half an arcsecond is also rare. The longer the scope, the greater the magnification...very long scopes (when you add a 2x or 3x barlow, for example) are diffraction limited, but they magnify the spot so much that you can actually see the "waves", or the rings of the airy disk around the central star's peak (also only possible with truly excellent seeing...less than that, and the star jumps around and gets warped, so you still can't get a diffraction limited spot.) The central peak of a star might be 0.5", but the whole airy disk is still there an visible, so the actual diffraction-limited resolution is less than 0.5". With most telescopes, a diffraction limited star is larger than 0.5". With some of the best telescopes on earth, such as a Planewave or an RCOS, you might get on-axis diffraction limited spot at ~0.4", and off-axis (corner) diffraction limited spot at ~0.6". Those telescopes cost tens of thousands of dollars.

With a lens like mine, or your average astrograph refractors or RCs, your on-axis diffraction limited spot is usually going to be quite a bit larger than 0.5" in the absolute best of conditions. Any off-axis spots are going to suffer from some kind of aberration...astigmatism, coma, field curvature, etc. Corner spot size in many scopes can be quite large, and often looks like little comets or out of focus blur.

992
EOS Bodies / Re: How do reds come out in your 5d3 ?
« on: August 13, 2014, 10:28:43 PM »
Tks guys for the responses.

Jon, I did try the per channel red.... but it did not fix the issue, just washed out the red. In real life the flower has more red chroma, and I can match it on screen, but then all details are washed out.... it's not that easy of a fix... moreover I'd like a perm fix rather than spending hours everytime I shoot red.

The only perm solution is to buy the widest gamut monitor you can find, run it in native gamut (NOT AdobeRGB, although even this would do you much better for reds (recall that the max 2D plot slice that makes it appear to have the same reds as sRGB gives a false impression, look at the full 3D gamut) but why clip off what the monitor can do since it can do more blue-greens, more purples, more reds and oranges than AdobeRGB) mode, and edit photo in ProphotoRGB 16bits. Even then some clipping will occur, but it will definitely be less than viewing in sRGB conditions.

Problems like these are why the display industry has set a hoped for target of no more small gamut displays after 2018, they want everything to be ultra wide gamut after that.

Yeah, I kind of skipped past screen gamut, but my screen does pretty well in that area (I think it's 97% AdobeRGB). I guess it is entirely possible that the reds I'm seeing on my screen still look overly saturated on K-amps screen. It is important to use a properly calibrated screen, and to perform your processing work in the widest gamut possible until you have good reason to convert to a smaller gamut.

993
EOS Bodies / Re: A Bit of EOS 7D Replacement Info [CR2]
« on: August 13, 2014, 08:04:37 PM »
Almost as important as the quantity and quality of AF points is the ability to link the exposure to the point you're using.  For me that's a big one.  Like when you have bright sky in the central region and focus point on the subject or the subject (bird) has a light head and a dark body and it's a portrait.  In the case of birds moving quickly from one position to another there is no time to fool with the exposure.  Bracketing isn't the total answer either.

I'd certainly would have had a 1DX by now if it wasn't so heavy for hiking.  There is a lot I love about my 6D but I'm really hoping the 7DII will be closer to the 1DX AF, then it'll be my second body for action and reach, no doubt.

Jack

Get Art Morris' book "The Art of Bird Photography", and read the chapter on exposure. It's probably the most enlightening bit of text on exposure I've ever read, and it completely changes how you think about it. You'll never have to worry about AF-point based metering ever again....it simply isn't an issue.

994
Thanks for the interesting test!
Sorry if I will repeat something that was already said (have no time to read all 10 pages...)
The results are not surprising for me.  You have tested a very specific situation, where APS-C will show an expected advantage. An exceptional lens was used, capable to deliver a very fine detail, which was happily recorded by smaller pixels of APS-C camera. Hence you've got a better detail. It is actually very simple. And because shooting conditions was good (low ISO, moderate aperture) you had no problems with possible noise and diffraction. It is known that in some cases APS-C has advantages. Another example: some time it is better for macro, because you can get better actual magnification and deeper DOF.
But, anyway, thanks for another point for keeping APS-C camera, after I finally will upgrade to FF! :)

The quality of the lens in this case really doesn't have much to do with it. The resolution is seeing limited, which reduces resolution much more than even diffraction. On top of that, a 2x TC was used, which also reduces resolution below the diffraction limit. If the image was diffraction limited, then yes, the 7D is going to make better use of the detail being resolved by the lens. But that was not the case...I was seeing limited.

If I did a test where the lens was diffraction limited, the 7D would probably take a greater lead than I've demonstrated here.

995
EOS Bodies / Re: How do reds come out in your 5d3 ?
« on: August 13, 2014, 04:36:00 PM »
Thank you all, especially Jon and McG.

Nice shot Mrs.... only that on my monitor, the flower shows as a deep burnt orange, not red  ;D

Same here. That looks like a some kind of Poppy, and they are usually more orange than red.

996
EOS Bodies / Re: How do reds come out in your 5d3 ?
« on: August 13, 2014, 03:12:36 PM »
Annnnnnd this is why I'm not a pro. 

Mackguyver:  ETTR is not new to me at all, I've been doing that for some time.  That principal is well in-hand for me.

But if I understood your and Jrista's posts correctly, I just learned that my in-camera WB does affect my RAW files due to its effect on metering.  That's a big deal for me, as I shoot everything in AWB and JPG+RAW, and I simply correct the white balance in my keeper RAW files.

So now I do need to sweat my WB.  I always thought that RAW alleviated me of that burden and I just focused on a general (non-color-specific) histo. 

Yes, metering can affect the exposure, especially in cameras that use some kind of color metering (which includes most of Canon's higher end models, most of Nikon's cameras, etc.) Color metering, especially metering that aims to prevent clipping, can definitely result in underexposure of one or two channels, while another is right at the limit. Auto WB can help with that, however it often results in inconsistent white balance frame to frame, so manually picking a good WB setting (and that does not necessarily mean using one of the built-ins...you can often choose by Kelvin or simply create a custom profile from a sample shot of a scene) is often critical to getting balanced color.

997
EOS Bodies / Re: How do reds come out in your 5d3 ?
« on: August 13, 2014, 02:29:25 PM »
Is exposure only a global adjustment for auto exposure modes?  Is there anyway to run auto-exposure independently for R, G and B?  I'm getting a headache thinking about how that would not work -- colors would shift, the metering may not work that way, etc. -- but please sate my curiosity and tell me anyway.   :D

- A
Exposure is exposure (shutter speed vs. ISO speed vs. aperture), and affects all channels, and there is no way to adjust one over the other.  They are not affected equally (but don't worry about trying to get into all of that as it's not helpful). 

Actually, exposure is JUST related to shutter speed and aperture. ISO is not really an exposure factor...it simply amplifies the signal that the exposure creates.

The key things to understand are that RAW files are recorded in a logarithmic manner and the highlights contain a lot of detail (in terms of data) while the shadows do not.  If you clip the highlights completely, the data is gone, but if you are near the clipping (i.e. Expose to the Right), it's easy to recover.  If you clip the shadows, it's totally gone and if your photo is underexposed, the detail that you can recover is mushy and noisy.

This is also fundamentally wrong. RAW data is recorded linear. Trust me on this...I do astrophotography, with DSLRs, and the linearity of the data is absolutely critical to being able to process the data correctly. In PixInsight, the processing procedurs are also usually split, between processing in linear mode, and processing in non-linear (post-stretch) mode.

The non-linearity of what we see in a tool like Lightroom has everything to do with the tool, NOT the data. The data is linear, it is rendered to the screen via non-linear tone curves, and non-linear processing.

So the idea is to get the data towards the right without clipping any of the channels completely (though a few small "blinkies" are okay), especially with flowers or other saturated color objects.  To do this, you MUST have an accurate histogram and White Balance has a huge effect on the accuracy.  The closer the WB is to the conditions, the more accurate the histogram.

You can expose to the right right up to the clipping point. Since the data IS linear in a RAW file, if you expose your red channel to 2^14 - 1, then your right at, but not over, the clipping point. You will not have lost anything.

The in-camera histograms are usually based off of JPEG thumbnails, which are actually highly inaccurate. This is why some people use UniWB, to change the per-channel weighting, and force the JPEGs that the histograms are based on to more accurately reflect the real dynamic range and clipping point of each channel.

Without UniWB, you can usually expose a little more than the in-camera histogram and "blinkies" would lead you to believe.

The resulting photo will look overexposed, but when you take it into a RAW processor and drop the exposure a stop or so, the photo will look perfect and you have lots of detail.  Plus, the shadows (i.e. saturated colors here) will also have more detail and latitude in terms of exposure and color adjustments.

There is one caveat...there is a very slight non-linearity to the response of the silicon in the sensor itself. That usually results in the uppermost levels near the clipping point tapering off in a small shoulder. It's best not to push exposure right up to the limit...i.e. 2^14-1. You want to keep your maximum levels just a little lower than that...2^14-10 or so is best. Otherwise, you'll notice that the highlights in those regions end up normalizing, becoming gray. You also start noticing very slight color shifts when you recover highlights that are right near the clipping point, as the processing algorithms are non-linear, and they will affect those upper upper highlights more than any other part of the signal.

Dropping the exposure by a stop or two is extreme. You want to ETTR, to maximize your use of the sensor's DR, but you don't want to push it too far. I'd say once you figure out where your real clipping point is, pull back by a third of a stop.

998
Photography Technique / Re: Questions about Shooting the Supermoon
« on: August 13, 2014, 12:42:06 PM »
Jrista, you are wright to tell us not to take a photo during full moon.

LOL, indeed. Here is an example of what you can get at half moon. This is my sharpest, most detailed single-shot image of the moon, taken on a day last winter where seeing was very good (very low atmospheric turbulence):



And here are the details:





Here is another half moon taken recently, during the Moon-Mars conjunction:




The moon is half again, but the detail isn't quite as good as in the first shot above. If you have a tracking mount, you could take a lot of frames of the whole moon, and stack them with an SR algorithm, and maybe get more detail when seeing is poorer.

999
EOS Bodies / Re: How do reds come out in your 5d3 ?
« on: August 13, 2014, 12:08:03 PM »
Certainly improved over the unprocessed RAW, but still not fully detailed.

Actually, the flower is fully detailed, for what detail was preserved in the RAW. That's why I posted the closeup...all the detail is there. The only additional thing you could do is adjust brightness or saturation further, or shift the hue...all of which will have the effect of reducing the impact of the reds overall.

I think what your looking for now is enhancing the subtle variations in the detail. That is where microcontrast and sharpening come into play...but that is a different discussion than restoring over-saturated colors.

Here is an image that has been sharpened:




I can much around the whites and blacks only and get it to where I want it, my issue is, why do I have to much around with it anyway. Is there an in body setting or LR profile I can use?

I think McGyver has some good ideas too.... the blues and yellows might be the issue and in trying to fix those, the raw converter over saturates the reds.

I tried the alt+white or black slider trick and while is made the reds better, the rest of the photo became unappealing.

I like my rendition (3rd shot) where I reduced both black and whites... and show the LR settings

Do you mean where you reduced the brightness and contrast of the image overall?

1000
EOS Bodies / Re: Canon 1dx vs Nikon d810
« on: August 13, 2014, 03:32:45 AM »
...also is it just me or does the Nikon have a green tinge ???

I don't know that it's green...but the skin does look pasty white, instead of the lively pink as in the 1D X image.

1001
EOS Bodies / Re: How do reds come out in your 5d3 ?
« on: August 13, 2014, 02:30:38 AM »
What do you think of this?



I chose the "Camera Faithful" profile under Camera Calibration. The settings can be seen in this before/after comparison:


1002
EOS Bodies / Re: How do reds come out in your 5d3 ?
« on: August 13, 2014, 01:58:53 AM »
Dropbox, OneDrive, Google Drive, etc.

1003
EOS Bodies / Re: How do reds come out in your 5d3 ?
« on: August 13, 2014, 01:28:53 AM »
Tks guys for the responses.

Jon, I did try the per channel red.... but it did not fix the issue, just washed out the red. In real life the flower has more red chroma, and I can match it on screen, but then all details are washed out.... it's not that easy of a fix... moreover I'd like a perm fix rather than spending hours everytime I shoot red.

You can get it right. It may just require tweaking all of the color channels. If your willing to share the RAW, I can play around with it.

1004
Landscape / Re: Rural Landscapes
« on: August 13, 2014, 01:24:16 AM »
South Coast NSW Australia

Wonderful shots! Love the wide panoramas.

1005
EOS Bodies / Re: How do reds come out in your 5d3 ?
« on: August 13, 2014, 01:18:34 AM »
You need to use per-channel color editing to bring down the red saturation independently of the rest of the colors. I've purposely increased the overall saturation on this rose photo of mine, then pulled down the reds, magentas, and purples to correct the oversaturation of the flowers without affecting the saturation of the greens:


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