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Archive 2012 · 5dmk2, problems with pure reds (and sometimes blues)
  
 
snapsy
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p.3 #1 · p.3 #1 · 5dmk2, problems with pure reds (and sometimes blues)


gdanmitchell wrote:
I've read that suggestion before, but I don't think it is going to work quite the way you imagine... unless you are going to be happy with the very "distorted" color balance that results. If you do want "natural" color - e.g. - very hot in one channel as in the original scene - once you compensate for the filter in post you'll be more or less back where you would have been had you simply avoided blowing out the hot channel at the time of exposure.


It works exactly as advertised. The filter adjusts the raw exposure levels of the channels, which can't duplicated in post by non-optical methods (such as lowering the overall exposure). If the only hue in the image is red then it wont matter, but every rose has its non-red thorn, not to mention a nice blue sky if the composition warrants it



Feb 04, 2012 at 03:57 PM
mpmendenhall
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p.3 #2 · p.3 #2 · 5dmk2, problems with pure reds (and sometimes blues)


gdanmitchell wrote:
Glass has nothing at all to do with this.


Comparing different lenses on the same body, I have seen color balance shifts up to 1/2 stop (and 1/4 stop level variations are not uncommon). This can be enough to make the difference between clipping or not if you are shooting right on the edge of color saturation. There could even be some truth to generalizing this to whole brands, since manufacturers often strive for a consistent color balance across their product lines; however, it really needs to be evaluated on a lens-by-lens basis.



Feb 04, 2012 at 04:03 PM
gdanmitchell
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p.3 #3 · p.3 #3 · 5dmk2, problems with pure reds (and sometimes blues)


snapsy wrote:
It works exactly as advertised. The filter adjusts the raw exposure levels of the channels, which can't duplicated in post by non-optical methods (such as lowering the overall exposure). If the only hue in the image is red then it wont matter, but every rose has its non-red thorn, not to mention a nice blue sky if the composition warrants it


If the only hue is red, than all the filter does is... ta da!... reduce exposure... just like using a smaller aperture or a shorter exposure.

If there are other hues, the balance among them will become unbalanced if the filter issued, and you will have to compensate (un-compensate?) in post to bring them back in balance again... thus effectively lowering their luminosity levels. Just as would have been the case had you used a smaller aperture, faster shutter speed.

Play it out with an actual exposure and I think you'll see what I mean.

mpmendenhall wrote:
Comparing different lenses on the same body, I have seen color balance shifts up to 1/2 stop (and 1/4 stop level variations are not uncommon). This can be enough to make the difference between clipping or not if you are shooting right on the edge of color saturation. There could even be some truth to generalizing this to whole brands, since manufacturers often strive for a consistent color balance across their product lines; however, it really needs to be evaluated on a lens-by-lens basis.


Several comments on this notion... First, I'm not quite sure what a "1/2 stop... color balance shift" actually means? Are you thinking of simple light transmission variations? That can happen, but that is a different thing than color balance, and it would still be a matter of off-setting the exposure to compensate for the hot color channel... and since the metering happens through the lens, in the end it would not have an effect on the amount of compensation required relative to the "normal" exposure using that lens.

And let's say that something you describe as a "1/2 stop shift in color balance" can be found between the two worst outlier lenses, and more typically the "shift" is less than "1/4 stop." By this description I presume you mean something like (to make up an example) that some lens reduces the luminosity of some color (that does not necessarily correlate precisely to a color channel on the sensor) by as much as "1/2 stop" compared to some other color. I'll make another wild guess that here in this "worst case" that the hotter color (let's say blue) might be 1/4 stop hotter than it should be and the less hot color (let's say red) might be a 1/4 stop less. This hypothetical difference is truly tiny and would rarely make a difference at all. I suppose that if you had some very faint detail just barely below the very brightest level in the hot color channel and you pushed the exposure right to and just barely past the "edge" that you might see some slight reduction in the contrast between these details. But that's about it.

(And notte that the OP came back and mentioned - a few posts above - a much larger compensation required to fix the problems with his red images.)

Two more points. First, the whole "lens coloration" thing tends to be grossly overblown by folks, many of whom buy into the mysticism of lenses with "wonderful color" and the like. Whatever color shifts lenses impart to images, generally I don't want them, but fortunately they are always much, much smaller than the color shifts we deal with based on changes in light coloration in our photography... and they are quickly and easily (in most cases) fixed in post.

Second, once again we are heading off on a tangent that has little to do with the real and practical solution to the OP's issue, and instead wandering off into Theoretical Land because, well, why exactly? As the OP reported a few posts up on this page... decreasing exposure in the images with exceptionally strong red fixed the problem. Simple. Easy. It works.

Dan



Feb 04, 2012 at 05:10 PM
snapsy
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p.3 #4 · p.3 #4 · 5dmk2, problems with pure reds (and sometimes blues)


gdanmitchell wrote:
If the only hue is red, than all the filter does is... ta da!... reduce exposure... just like using a smaller aperture or a shorter exposure.


RIght. That's the point of using color filters, to balance the channels when one hue dominates but there are other hues in the photograph that are important to you, hence my rose reference. And the OP showed his photos have other hues than red.

gdanmitchell wrote:
If there are other hues, the balance among them will become unbalanced if the filter issued, and you will have to compensate (un-compensate?) in post to bring them back in balance again... thus effectively lowering their luminosity levels. Just as would have been the case had you used a smaller aperture, faster shutter speed.

Play it out with an actual exposure and I think you'll see what I mean.


I use color filters so I'm speaking from experience. It is of course implied that you need to rebalance the color to restore the original hues. You can either do that entirely in post or baseline the process by setting WB in the camera with the filter on. And you only need to lower the other channel luminosity levels (rather than rebalancing just their hues/WB) if the artistic needs demand. And if you do wind up lowering the luminosity in post then the result is a multi-stop improvement in those channel's noise levels compared to shooting those channels underexposed without a filter. I know you're keen on remarking how noise doesn't matter in modern cameras but if presented with a choice of a color channel having the effective noise of ISO 400 instead of ISO 1600 which would you choose?

You've shot and processed tens of thousands of photos and never had the need to use color filters? Were all those photos in a cave?



Feb 04, 2012 at 05:37 PM
gdanmitchell
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p.3 #5 · p.3 #5 · 5dmk2, problems with pure reds (and sometimes blues)


snapsy wrote:
You've shot and processed tens of thousands of photos and never had the need to use color filters? Were all those photos in a cave?


I used color filters decades ago when I shot black and white film - used them a lot. I used them when I shot slides, obviously, since "color correction" had to be done at the time of exposure. (Selecting the old indoor/outdoor films was also part of the equation.)

But, no, I do not use a single color filter with digital. The only filters I use are neutral density filters (not GND) for allowing me to use longer exposures and/or larger apertures and polarizing filters for the reasons we all know about.

Color correction in digital post is far more powerful and far more flexible that color correction in, uh, "pre" using color filters. I have tremendous control over nature of the color shift, its magnitude, and where it does and does not occur in the image. For example, in an image with multiple color sources with different temperatures I can adjust them separately in post and I can fine tune the amount of the adjustments and feather their boundaries.

So, no. I don't use color filters and have no reason to.

Very few - almost none, actually - were shot in caves. But among them are photographs shot in a wide range of lighting conditions: music/theater performances under stage lighting, a lot of night photography of subjects ranging from natural to urban, a wide range of nature and landscape work, some sports photography, etc. http://www.gdanmitchell.com/

Dan

A few nature images in which the color balance issues were acute and were handled in the way I describe. (The poppy image includes some areas that are still subject to "the problem," but it was a choice here and it seems to work.)




















Feb 04, 2012 at 06:52 PM
 

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snapsy
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p.3 #6 · p.3 #6 · 5dmk2, problems with pure reds (and sometimes blues)


gdanmitchell wrote:
But, no, I do not use a single color filter with digital. The only filters I use are neutral density filters (not GND) for allowing me to use longer exposures and/or larger apertures and polarizing filters for the reasons we all know about.

Color correction in digital post is far more powerful and far more flexible that color correction in, uh, "pre" using color filters. I have tremendous control over nature of the color shift, its magnitude, and where it does and does not occur in the image. For example, in an image with multiple color sources with different temperatures I
...Show more

Color filters are not mutually exclusive with digital post processing. They can only be replaced completely with post processing at the expense of noise and thus signal/detail. It can certainly be debated whether this loss is acceptable for given content, print sizes, etc.. but for me it is not.

gdanmitchell wrote:
Very few - almost none, actually - were shot in caves. But among them are photographs shot in a wide range of lighting conditions: music/theater performances under stage lighting, a lot of night photography of subjects ranging from natural to urban, a wide range of nature and landscape work, some sports photography, etc. http://www.gdanmitchell.com/


Yep, I'm familiar with your work (cave comment was in jest) and I'm definitely a fan. I'm less a fan of your dismissal of the finer technical aspects of digital photography, although I think I understand your reasons for doing so, ie your zeal to keep the focus on the art and broader technical aspects, which you believe have much higher importance than the minutia. I can't argue against that position because the relative importance of those broader aspects is of course higher. But once those broader aspects are understood (I wont use the word mastered) there are finer aspects which should not be left unexplored or dismissed.




Feb 04, 2012 at 07:57 PM
Ralph Conway
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p.3 #7 · p.3 #7 · 5dmk2, problems with pure reds (and sometimes blues)


Red is not the problem. Red light is. But not with Canon only. Same with Nikon, Sony, Pentax. Shoot a concert with red light from and no additional and you can forgett about it.


Feb 04, 2012 at 08:07 PM
Access
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p.3 #8 · p.3 #8 · 5dmk2, problems with pure reds (and sometimes blues)


snapsy wrote:
Another alternative is to use a color filter (cyan in this case), which change (balance) the temperature of light and let you keep a higher exposure without blowing a channel.

Yes, I got one of those a few months ago for those type of situations where I am shooting under the heavily decorative lighting that tends to fall around 2500-3000K. Because in those cases I am re-balancing in post to get 'good' white balance (can be a very subjective thing) rather than wanting a faithful color reproduction of the scene. I haven't used the filter that much, it's a tradeoff like most things, you trade lower ISO and/or faster shutter speeds for getting back some of that dynamic range on the blue channel that you lose under the ~2700K lighting.

But last weekend I was just trying to get proper exposure outdoors (with faithful color reproduction). Though I guess in theory I could have shot with the filter and then taken out the blue/turquoise cast in post. That might help if, say, the green or blue channel(s) are suffering from being underexposed (like missing shadow detail).

I'm not much of a brand person, honestly my focus is on the people and the photography and I only think about brands or technical aspect when I have to (this was one of those times). I do believe the Panasonic I sometimes use has less dynamic range than the 5d2, which is probably why this happens a little more when I use it.



Feb 05, 2012 at 03:17 AM
gdanmitchell
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p.3 #9 · p.3 #9 · 5dmk2, problems with pure reds (and sometimes blues)


Access wrote:
I'm not much of a brand person, honestly my focus is on the people and the photography and I only think about brands or technical aspect when I have to (this was one of those times). I do believe the Panasonic I sometimes use has less dynamic range than the 5d2, which is probably why this happens a little more when I use it.


Now, now. That is way to much common sense for a photography forum! ;-)

Take care,

Dan



Feb 05, 2012 at 04:59 PM
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