sploppert Loc: Rochester, NY

Imagine a checkerboard consisting of pure black and pure white squares. Now take a well-lit picture of it in such a way that the checkerboard is the only thing that fills your frame. 50% black, and 50% white. We know that black absorbs light and white reflects light, and that nothing is darker than black and that nothing is lighter than white. Here's the question: Do you know how much light is being reflected by the checkerboard?
If you guessed 50%, then you're wrong. The answer is 18%. In fact, they've discovered that 18% is the amount of light that's reflected from an overwhelming majority of the scenes that we see. I can't find anything online that explains why that is, but it's so commonly accepted by the scientific community that it's become the basis for the light meters that are built into every modern digital camera that each of us owns and uses every day. That is, the light that comes streaming through our lenses (aka "reflected" light) is ASSUMED to be 18% of the total light hitting our subject (aka "incidental" light). All of our camera's automatic exposure adjustments for that shot are made accordingly. We think that our cameras are so clever for getting exposures right as often as they do, but in fact the only ones they're getting right are those where the reflected light is in fact 18% of the incidental light!
Too technical? I agree. Still, it's about getting good pictures - "editing before the fact", if you will - so let's try one example: Take a closeup picture of a pitch black cow. Because black is dominating the frame, the amount of light that enters your lens is tiny - let's say 5% of the light of a snowy scene on a bright day. Your camera's light meter doesn't know anything about black cows: It only knows that it has to somehow bring that light up to 18%, and so it INCREASES exposure until your black cow becomes a faded gray instead of black. And your snow scene? It's the same thing, except in reverse: Your camera DECREASES exposure until the snow becomes a dingy shade of gray as your camera tries to reduce all that white to 18%, rather than the 95% that it in fact is. In short, our light meters do a good job when a scene is already moderately lit, but in very bright or very dark conditions, they're as dumb as a post.
The remedy in both cases is counter-intuitive: Our eyes see the picture our camera produces of a dark gray cow and interpret it to be black, but the picture itself is wrong! Dark images that SHOULD BE dark can benefit by moving your exposure compensation DOWN (-EV). Bright images that should be bright - "gray snow" shots - can benefit by the opposite. For more information and some great illustrations of this, see http://www.scantips.com/lights/metering.html

Roger Hicks Loc: Aquitaine

All pretty much spot on, especially the point about corrections for reflected-light metering being counter-intuitive, but there are three things worth adding. First, it's 13-14%, not 18%. Second, multi spot metering MAY introduce some useful corrections, but unfortunately, you can't always tell what they're going to be. Third, optimum exposure for digital (and slides) is based on not 'blowing' the highlights (let the shadows go hang) while optimum exposure for negative film is based on not 'blocking' the shadows (let the highlights go hang).

Cheers,

R.

BboH Loc: s of 2/21, Ellicott City, MD

Waht else is new? Besides, that is, Jersey, York, ?Caledonia, Mexico, Hebredies?
Your DID put it very nicely.

rpavich Loc: West Virginia

Lol....I'm glad this rant came from someone besides me... :)

My fix is easier than guessing on the amount to monkey the exposure around to try and correct the black cow/white snow shots....

Get a meter and don't worry about what color the subject is....black cow, white snow...it's the amount of light FALLING ON that cow or snow that matters...not what's reflected back...If I had a dollar for every thread where I read "I can't figure it out...why did my picture come out so dark?" or "why did my camera overexpose my shot?" I wouldn't have to work...and then come the suggestions to make things even more complicated by remembering to try and figure out how to second guess the camera in which situation and how much...to try and get an exposure that you only will find out if it's actually correct until later on in your computer.... :(


Ok...closing the door of my bunker...hunkering down...army helmet on? Check.....sandbags in place? Check....

Ready.

Roger Hicks Loc: Aquitaine

Almost. But not when you're shooting negative film. You can increase the exposure a LONG way with negatives (which you may often want), getting more and more detail in the shadows, before you start 'blowing' the highlights.

Also, you may still have to interpret/fudge incident readings. You want detail in white snow, or the whitewashed walls of a Greek village? Cut the exposure slightly: up to a stop, maybe. You want detail in the fur of a black cat, or a black fur coat? Increase the exposure a bit: again, maybe a stop. You want detail in both the black cat's fur and the white snow? You'd better be pretty good at metering for your chosen medium AND understand post-processing.

Cheers,

R.

rpavich Loc: West Virginia

Yeah....I know, but I didn't want to make this more complicated than it already was...I was just pointing out the difference between the dumb camera and the incident meter...if the dynamic range is within the camera's ability to record in one scene...then you should have no problem with that black cat on white snow...but even then you'd have to figure that out no matter what kind of metering you are doing...true?

I was just saying that getting a meter would go a long way towards fixing a lot of the simple exposure issues that are posted on the 'hog everyday.... :)

oldtool2 Loc: South Jersey

Ah, here we go again! Got ya beat Bob, building a bomb shelter.

Of course you are right. With out a meter I never would have gotten the right color on this shot. I now know why it is called a Great BLUE Heron. Thanks Bob.

Jim D

DennisK Loc: Pickle City,Illinois

lol,when I saw the title of this post,I thought the OP was referring to the tool between our ears. :)

Roger Hicks Loc: Aquitaine

Very true indeed!

My intention wasn't to correct you, which of course was what the post looked like, for which I apologize. Rather, I wanted to remind anyone else who took your excellent advice that they can't just blindly follow an incident meter either, though as you say, most of the time you can.

Cheers,

R.

rpavich Loc: West Virginia

Got it....thank you for clarifying..you are correct! :)

oldtool2 Loc: South Jersey

Bob, you got me back to using a meter as you know. I admit I do not use it all the time but there are times it can't be beat! Here are two more examples of when a meter came in very useful! There are a few blown spots on both sshots but if not for the meter they would have been completely blown, than you.

Jim D

jenny Loc: in hiding:)

But basically it is your usual rant,you can't seem to use the reflective meter in your camera and know how much exp. comp. to use. You keep telling people to use an incident meter which is an entirely different animal,meanwhile the newbies read this sort of thing and think they need one....
and furthermore,18% has always been a term printers use,just don't question it.

rpavich Loc: West Virginia

That's great to see Jim...good shots and you are very welcome!

rpavich Loc: West Virginia

Actually...I never said that I can't...I merely said that the meter can be fooled and there are two ways to deal with it.

I hope newbies read this and think that they need one...I surely do...or at least be open-minded enough to investigate the possibility that it will help them get better, more consistent exposures.

I would say that it would help you to get more consistent exposures but you haven't started any topics by posting any so I don't know.

jenny Loc: in hiding:)

Actually i really did get into the subject of exposure one day with the result that you didn't even consider what i was saying before immmediately posting a "yeah but" reply just like a smart kid not willing to listen.