Curious question while reading "Understanding Exposure"

Since I'm a new DSLR user, I've read here in the fora (or forums) that as a beginner I should read up on "Understanding Exposure" by Brian Peterson.

So grabbed the book and have been reading and what a great book it is.

Now, as I was reading through the side notes for the photos, I noticed something that I just can't wrap my brains around. In a few photos that Brian showed, he mentioned following the steps below (I believe I've seen this in frontlighting and/or sidelighting):

• Set Aperture to f/22, for ex.
  
• Set focus so anywhere from 2ft to Infinity are in focus
  
• Then he pointed the camera up to the sky above, just above the horizon and adjusted the shutter speed until he gets the correct exposure
  
• The he recomposes the shot
  

When you meter a scene, your camera will give you an expsoure it thinks is correct. It is basically saying to you... " if I assume that what you are pointing at has the same relectiveness as mid grey(18%) then this is the exposure you want".

Now clearly if you are pointed at something white the camera, assuming that you are pointing at something with 18% reflectiveness, will underexpose. Point at something black, the camera will overexpose. (white DOWN TO Mid grey. Black UP TO mid grey). You therefore need to interpret the scene and add exposure compensation as required.

Now, to answer you question about the Blue sky, as far as exposure goes, it reads/meters about the same as 18% reflectiveness. So, point the camera at the blue sky to get a good meter reading and then recompose the shot.

You might find it useful to also read up on something called the "Zone System".

What metering was he using?

The one problem that I had with that book is that he never, once, actually defined "correct exposure". Needle, dead center of the meter is only "correct" if you're metering area is filled with a subject that is a properly, mid-gray tone (18% or 15%, depending on who you ask...percentages have never mattered for me, really). Anything else will require exposure compensation to set the meter where it needs to be.

I'd have to go back and look at my copy to see what the conditions were that he as shooting that under. Do a Google search for Zone System or modified Zone System and do some reading on that for some great reference points for exposure.

Paolo.Leviste wrote in post #15053923
What metering was he using?

Probably evaluative, but it doesn't really matter. Whichever method one uses, the camera still equates what it is pointed at to 18% grey. Thereafter, it is down to the photographer to analyse the metered scene, determine just how close it is to 18%, and apply compensation as required.

Don't give "metering" too much credit, it's not magic. Basically the camera will meter by grabbing all the pixels in the requested area (evaluative is wider than spot, etc), and average them. In manual mode, it will show you how many stops you are away from 18% gray via the needle. In automatic modes, it will set the shutter/aperture/iso (depending on the mode) such that the average of those pixels will render at 18% gray and put the needle dead-center for your amazement.

It normally works fine as shown by the 99% of folks who use automatic modes in their camera to get decent exposures, but if you *know* something is close to 18% gray, it's far better to meter off that (hence the existence of gray cards) and not guess that the pixels in the landscape do actually average out to gray.

This all assumes of course that you *want* 18% gray to be the correct exposure for the scene. Shooting a polar bear in the snow probably wouldn't be the best place to make that assumption.

Dave

I'm not a big fan of that book because he leaves out critical details. When he talks about metering the sky, this is what he really means:

You want the sky to be bright in a photo, but you do not want to let it blow out (blue becomes white). So you can pick an aperture and then pick a combination of ISO and shutter speed that has the needle pointing at about +2 when pointed at the sky. This will give a correct exposure.

Point that needle in the center while metering the sky and the shot will be massively underexposed.

The other problem with Peterson is that his book is film based thinking. He always treats ISO like it is a fixed value while he is setting his exposure. This is a terrible approach for a digital photographer because ISO is pretty much the least important variable at your discretion.

My general approach is to always pick aperture for DOF, shutter speed for motion or shake and then pick ISO last in order to get the correct exposure. I only return to the first two picks and compromise if the ISO level is outside of the range of the camera (or outside of what I feel is usable with the camera). I would never pick ISO first.....that's film based thinking.

You have Live View on that camera, that's where to learn exposure...just point it at your scene with the histogram showing on the LCD and make your adjustments based on that histogram.
You want that histogram just shy of the right side, insuring no blinkies are flashing...make your adjustments based on changes to that histogram.

Spot meter the blue sky about a stop and third over. This works great on days with clear skies.

Paolo.Leviste wrote in post #15053923
What metering was he using?

What you have to remember is that the majority of that book was written in 1990 so it's written around a film camera. It's been updated twice, but the greater mechanics of that book is 20 years old.

He's metering on blue sky, provided there is blue sky, to get a clean subject to meter off of instead of what may be a very busy scene with different colors as well as dark areas and bright areas. You could substitute "blue sky" with "grey card".

Sorry, all. I was replying from my phone, so my post wasn't as...enunciated as I would normally. But thanks, all, just the same.

DunnoWhen wrote in post #15053910
Now, to answer you question about the Blue sky, as far as exposure goes, it reads/meters about the same as 18% reflectiveness. So, point the camera at the blue sky to get a good meter reading and then recompose the shot.

But what if it's a clear day with a blue sky . . . and what you want to photograph is in the shade under a tree?

It seems like his method would only work if you happen to be photographing something that is out in the open. How often does that happen?

I'm sure this method works great if you're shooting something that is receiving light from the sky in an unobstructed manner. But for all else it seems like it would be way, way off.

Tom Reichner wrote in post #15056784
But what if it's a clear day with a blue sky . . . and what you want to photograph is in the shade under a tree?

It seems like his method would only work if you happen to be photographing something that is out in the open. How often does that happen?

I'm sure this method works great if you're shooting something that is receiving light from the sky in an unobstructed manner. But for all else it seems like it would be way, way off.

The blue sky isn't the only method recommended. Personally I have found that turning away from the sun and using the sky to meter from as fairly effective when I'm outside, otherwise I look for a neutral source like faded asphalt, sidewalks, or the other method mentioned in the book, grass. Personally I found that book to be more useful then many of the subsequent books I've read since then. It presents the information in a straight forward, easy to digest manner. The whole point of the book is that someone can be completely green and after reading the book they should be comfortable shooting fully manually, and knowing why they are choosing the settings that they are. It was never intended to be some sort of photography panacea.
It's very easy to second guess it as a knowledgeable photographer, but we have to remember how easy it is to become overwhelmed when your knowledge level starts at 0. Think about how many times someone completely new to photography posts up a very simple question and in the process of answering it the respondents spiral into some semantical discussion of technical theory; leaving the newbie completely bewildered. The book does a good job of getting people through that "bewilderment" stage and putting them in a place where they have the confidence and basic knowledge to move on without the doubt and second guessing that can arise from the multitude of opinions they encounter on the web. Granted I speak from experience. The only issue I had after reading that book (and I couldn't even turn my camera on before I read it) was that I ran around for days shooting at f/22 whenever I wanted a large subject completely in focus.:o:o

^ I agree with this.

The other thing to remember is that the book gives you specific examples and tells you his solution for that specific example. You could start to add "what if's" to every example and the solution would be different.

What if the subject was moving?
What if it was cloudy?

You can't take each example as a gospel of how to shoot. Its just an example of how to figure it out for yourself. Thats why he uses terms like "the correct exposure" instead of center the needle. Your creativity and the subject matter will influence whats "correct" for you.

Tom Reichner wrote in post #15056784
But what if it's a clear day with a blue sky . . . and what you want to photograph is in the shade under a tree?

It seems like his method would only work if you happen to be photographing something that is out in the open. How often does that happen?

I'm sure this method works great if you're shooting something that is receiving light from the sky in an unobstructed manner. But for all else it seems like it would be way, way off.

As the others mentioned, there are other things to use a guideline; green grass/bushes (not precise but gets you really close), water, skin, etc. Plus, you can use white or black, just knowing that they'll be *around* +/-2, respectively. Stop sign red is remarkably close, too, interestingly enough.

Once you start getting a feel for the results you get from different subjects like that, it gets a lot easier to identify and predict where your exposure's going to be.