What's with this "ERADR" and "EBTR" stuff?
It turns out that most, if not all, consumer/"Pro-sumer"/professional digital cameras are supplied with some amount of dynamic range in excess of that implied by the dynamic range of the JPEG-adjusted histogram and the JPEG thumbnail image provided by the cameras software. Even if you are capturing RAW data, the histogram and thumbnail are specifically attuned to the Dynamic Range ( number of "stops"/E.V.S) allocated to JPEG files extracted from the RAW data collected with each exposure.
There is, beyond the JPEG file's dynamic range, some additional "headroom" of dynamic range there to be used by RAW capture. It may be as little as 1/3 of a stop, up to two full stops ...or more...depending on your particular camera. I say "your paticular camera" because in several instances in which more than one camera of a given camera model has been tested the " Extra RAW-Accessible Dynamic Range" (ERADR) has differed by as much as 2/3 to one and 1/3 stops. Thus, each camera must be tested for its unique amount of ERADR.
Why test for ERADR? Its a crap-shoot!, If yor camera has only 1/3 stop of ERADR, you'll wondrr "Why did I waste my time?" But if your camera can provide you with one to two full stops of additional ERADR, Wouldn't you like to use it? For example if DXOmark rates you new camera's sensor at 12 E.V.S ( landscape) but you find it can provide 13 and 2/3 or 14 full stops, wouldn't you like to use its full complement of dynamic range? An additional two full stops of exposure? Why leave that sitting unused,on the table (or in your sensor?)
It's not brain science...or rocket surgery...to figure out your camera's ERADR.
Figure your camera model provides 11 stops of DR for a JPEG file and the right end of the histogram is where you start clipping highlights.
Set your camera to manual exposure, manual focus, and pick a chosen WB (not AUTO WB).
Choose a scene with a DR that falls within your camera's stated DR. and, for greatest accuracy, do it on a somewhat dull, overcast day and make sure the scene includes some highlights with faintly discernible detail ( zone VIII if you are a zone System user) .
With your camera on a tripod, set your exposure so the right end of your histogram (the "light pile") just barely touches the right end of the histogram frame. That's Exposing to the Right (ETTR).
Then take make a series of additional exposures increasing by 1/3 stop of shutter speed (1/3 slower shutter) until you've shot, say, three additional full stops of exposure ( nine exposures - each 1/3 stop brighter than the previous one). This is Exposing Beyond the Right (EBTR)...beyond the right of the right end of the ol' JPEG histogram frame.
Download the exposures into your computer and open in Adobe Camera RAW,
The thumbnails of these exposures will look overexposed and washed out because if they were JPEG files, they would be. But these are RAW captures taking advantage of the Extra RAW-Accessible Dynamic Range.
You will show these to be properly exposed RAW data by moving the "exposure" slider to the left and tonally normalizing the image. Open, and tonally normalize each image intil you finally find an exposure in which the highlights actually are clipped of their detail. Those exposures not showing clipping tell you your camera's ERADR.
Five additional exposures without clipping? One and two-thirds stop of ERADR.
two additional exposures without clipping? 2/3 st of ERADR
Three additional exposures without clipping? one full stop of ERADR.
Six additional exposures without clipping? two full stops of ERADR.
See? Easy! ( I would say "easy peasy"..but that just sounds unduly weird ')
So, when to use that ERADR? When you really need that extra DR!
On a bright, sunny day, there's no need unless you are after a supper fast shutter and a super small aperture and a low ISO.
But EBTR comes into its own under less-than-ideal lighting. Find your ETTR exposure, then add your camera's ERADR, and ,"there y'go," or "Bob's your uncle!" or "That's it", or "you done it"....or whatever you like to say at such a successful juncture of events.
It's all based upon and derived from what I consider to be the basic Canon of Digital Exposure Knowledge:
Reichmann, Michael, essay in Luminous Landscape, 2003
"Expose Right"
http://www.luminous-landscape.com/tutorials/expose-right.shtml...and a follow-up in 2011:"Optimizing Exposure"
http://www.luminous-landscape.com/tutorials/optimizing_exposure.shtmlFraser, Bruce,
"RAW Capture, Linear Gamma, and Exposure"Adobe White Paper, 2004,
http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdfFraser, Bruce, and Jeff Schewe, "Real World Camera RAW.
Peachpit Press, 20O9,
Schewe, Jeff, "The Digital Negative", Peachpit Press, 2013
Schewe, Jeff, "The Digital Print" , Peachpit Press, 2014
The bottom line is the need to realize that the basic principles of proper film/jpeg exposure and proper RAW data exposure are two completely different concepts.
Vive la difference!
I got quickly sold on the logic and visible proof of ETTR and then as quickly began experimenting with EBTR which I've now happily and productively used and taught EBTR for almost a decade.
Try it!
You'll like it!
If you don't, what's wasted....oh....that's right ...the cost of all those wasted exposures!!!!
Best regards,
Dave Graham