brainiac wrote:
OK - I can see I'm not getting through here. First, HTP was switched off. This is 200 iso. Secondly, the exposure has not been adjusted in post.
Based on my experience shooting the 5D, understanding post-processing approaches pretty well, and printing, you just described the problem.
You would describe your exposure as correct for the look you wanted. I would agree... if you were shooting transparency film.
However, I would describe your exposure as wrong for this scene when shooting digital. I would have increased the exposure considerably. It would have looked wrong on the LCD display. The unaltered imported RAW file would also have looked wrong.
After simple work with levels, curves and so forth...
... the print would have had the same "look" you are going for but the image quality would have been excellent. In particular the "noise problem" would have been a complete non issue in the print. The whole "issue" presented by this image would have been no issue at all.
Digital has the dynamic range that digital has. If you go beyond that at the high luminosity end of this range you blow the highlights and lose detail in such a way that it may not be recoverable. When you push the lower end of the luminosity scale, by definition you reduce the signal to noise ratio of your image and noise can start to become an issue. Banding can also become an issue because you have only a few levels of data to work with.
On an image like this one where dynamic range is rather narrow, the correct exposure increases the signal to noise ratio (e.g. - reduces noise) by "overexposing" by the standard that you might have used with transparency film - but that is the "correct exposure" in this case. (The correct exposure is not always equal to "the exposure in which the luminosity looks a lot like the original scene." Done much night photography? :-)
You raised the question of what to do in a different sort of image in which the dynamic range exceeds that of the camera system? That is a valid question, and it is one that also has to be addressed with any camera, digital or film. As I suspect you know, there are a variety of ways you can choose to handle that scenario:
1. You could choose to blow out highlights. Typically this is not the best approach but there are situations where it could be - for example if the blown highlights are small specular highlights. This approach sacrifices highlight detail in favor of shadow details (and, on digital, lower noise.)
2. You could choose to expose for the highlights and lose shadow detail - and, on digital, also have to think about shadow noise and banding issues. In general, my preference is to choose this over #1, but every shot is different. By careful and informed post-processing (the digital equivalent of the venerable dodging and burning, plus techniques that are only realistic in the digital darkroom) I can usually manage the shadow noise and get sufficient shadow detail for a fine print.
3. In extreme cases you can do what film photographers have done for years when faced with certain scenes with this "problem" - use graduated neutral density filters. Again, I'm sure you already know this, but grad NDs can provide a good way to handle the situation where one portion of the frame (e.g. sky) is "too bright" and another (e.g. foreground) is too dark. There are limits to what you can do with this, but it clearly can be another viable way to deal with this.
4. Depending upon your subject and shooting methods, another excellent technique is to exposure bracket and combine in post. While there are certainly situations in which this is not a viable option, in many others it is the best option.
There is nothing new here. Underexposure creates certain problems. Overexposure creates certain problems. Super wide dynamic range creates serious challenges. If you bring to bear your understanding of the issues and techniques to resolve them you can get an excellent photograph. The specific techniques vary depending on the shot, your goals, and the medium in which you shoot.
For me, the bottom line is that this thread is a classic tempest in a teapot - a lot of fuss about not much. There is nothing new here - it is important to choose the best exposure for creating the image you have in mind, and here simply choosing a different exposure would have accomplished that without the shadow noise in the original post. Photographers have dealt with these types of limitations in their media for the entire existence of photography - part of the "game" is understanding how the process works and then figuring out the best way to deal with it.
Dan