Hello Keith,
As Bill Janes said in dpreview D3/D700 forum - "Iliah Borg is an expert but he talks in riddles"........so even after going thru his and Lexa's articles pertaining to "Centered-exposure", I still don't get it.
1) How do you implement "centered-exposure", again relative to D3/D700 if applicable? why? has it reference to the Zone System?
2) How is "centered-exposure" different and or compared to "Zone VII exposure"?
3) What is the exposure technique without reference to the Zone System?
Thanks,
jaime
Jaime,
Thank you for asking the question. Iliah is essentially contrasting two exposure techniques, "expose to the right" (ETTR) and the normal process of exposing for a mid-tone ("centered exposure"). The basic premise behind ETTR is that your histogram should just touch the right side of the display, with no "clipping." This is good advice in general, but can cause underexposure in some situations. Iliah's primary point is that ETTR, done blindly, can result in underexposed mid-tones, noisy shadows and desaturated and low-contrast (poor quality) images. Instead, he recommends "centered exposure," which is essentially the same as exposing for Zone V in the Zone System (or, in some cases, following the recommendations of your metering system instead of using negative exposure compensation to "save" the highlights.)
The problem he is addressing is that many photographers over-compensate when trying to protect the highlights using ETTR. Instead of trying to protect the "important" highlights, they try to protect all of the highlights, even "specular" highlights and bright light sources, which proponents of the Zone System would advocate shouldn't be protected. The problem with trying to protect
all of the highlights, is that you will significantly underexpose mid-tones and shadows.
This leads into your second question, which is "how is centered exposure different and or compared to Zone VII exposure?" Iliah doesn't really define "centered exposure" but implies that it would be the equivalent of exposing for Zone V. So, you could be using "centered exposure" by using your recommended meter reading (which attempts to expose for the mid-tones) or by using a more deliberate process of spot metering and exposing on Zone V. "Zone VII exposure" is a better compromise than either ETTR or centered exposure. If you are exposing for Zone VII, that means that you are metering on the brightest part of the scene that contains important detail and setting your exposure to record this region of the scene as Zone VII (i.e., it will be rendered as bright as it can be rendered and still retain visible detail). If you use Zone VII exposure, you are appropriately protecting the highlights that should be protected (Zone VII), and letting Zones VIII, IX and X render with less detail. Zones IX and X will be "blown out" according to today's criteria, which is exactly how they would have been rendered using the Zone System. Zone V might be slightly under-exposed when you are exposing for Zone VII, but not by much, and this slight under-exposure can easily be corrected in post processing, in contrast to the poor quality results that you might produce when underexposing by up to 2.5 stops when using the ETTR technique.
The "centered exposure" technique "without reference to the Zone System" would be to spot meter on a mid-tone and expose accordingly.
I have to be honest that when I am shooting "casually" I often let my exposure meter determine the exposure, but check the histogram to ensure the exposure isn't being overly influenced by dark or light areas of the scene. When I am shooting more deliberately, I will meter for Zone VII and expose that region of the scene at +2.0EV, ensuring that I retain visible detail in this "important" highlight area.
I hope this helps. Please ask more questions if my explanation isn't clear.
Keith
