Exposure in 7 Shots

Got 2 minutes?  ...like literally, 120 seconds?  Sweet.  Grab your camera, we're going to take 7 quick shots and demystify this exposure setting stuff once and for all.

Shot #1:

Pick up your camera and walk outside onto your front steps, breezeway, or whatever.  Just get outside.  Set your camera's Exposure Mode to Aperture Priority (for most cameras, this means turning the dial on top to "A").  Now, set your aperture to f/5.6.  Find something nearby to focus on, about 3 or 4 feet away.  I used the broken flag bracket on my front porch.  Make sure that whatever's in the background is decently far away, like your neighbors house or a tree across the street.

Next, look at your shutter speed.  To avoid screwing with more settings later, we want it to be about 125 right now.  If its lower than that, gradually increase the ISO setting on your camera until you end up somewhere between 100 - 160 on shutter speed.  If your shutter speed is higher than that, gradually step down your ISO until you get in that range.  Just to get you in the ballpark, if its bright and sunny outside your ISO will probably be 100 or 200.  If its cloudy or moving on towards dusk, it might be 400, 800 or maybe even 1600.

Reframe your shot, focus on the nearby object you chose, and pull the trigger.

Shot #2:

Change your aperture to f/16.  Reframe, focus on the same nearby object, shoot again.  That's it!

Now compare Shot #1 vs. Shot #2.  Notice that the nearby object (my flag bracket) is equally in focus in both images.  But look at the difference for the far away objects in the background.  They are blurry in the first shot, taken at f/5.6 (shallow depth-of-field).  They are much sharper in the second shot, taken at f/16 (deep depth-of-field).  Congrats, you now understand aperture's effect on depth of field!

Shot #3:

Turn around, open your door, and take a shot into your house.  Its much darker inside, so you should hear your shutter take its sweet time opening and closing.  Look at the picture and zoom in.  See how blurry everything is?  This is because you are hand-holding the camera at a very slow shutter speed.  What you're seeing is the dreaded "camera shake"!

Shot #4:

Walk back outside.  Set your camera's Exposure Mode to Shutter Priority ("S").  Set your shutter speed to 500 (1/500th of a second).  Hold out your free hand and focus on it.  Now pull your hand back, and swing it slowly through the frame.  Shoot when you see your hand in the middle of the viewfinder.  Check your shot.  See how your hand is frozen in place?  (If it's not, you were pretending to pitch a fastball, so slow down and try again.)

Shot #5

Set your shutter speed to 125 (1/125th of a second) and do that thing with your arm again.  Swing it the same speed, shoot when it hits the middle.  See how your hand is all blurry?  Now you understand how shutter speed effects moving objects.  Fast shutter speed = frozen in place.  Slow shutter speed = movement looks blurry.  Two more to go!

Shot #6

Set your camera's exposure mode to Program Mode ("P").  Change your ISO to 1600.  Shoot something, subject isn't as important this time.

Shot #7

Dial your ISO down to 100.  Reshoot the exact same shot.

Compare shots #6 and #7.  Zoom in allll the way on the same area in both shots.  See the grainy speckles in shot #6 (ISO 1600)?  That's noise.  See how much smoother everything is in shot #7 (ISO 100)?  Now you understand the affect of ISO on image quality!

DONE!

Exposure Compensation

Bad news... I've been holding out on you.  Now that I've made you learn all this stuff about metering and manually exposing your images I'm going to give you a shortcut.  An awesome shortcut you will use all the time like I do.  Nothing wrong with it, because sometimes saving time is the difference between getting the shot and missing it.

So what is it?  It's exposure compensation.  It's the quickest way to make an image brighter or darker and it works in every exposure mode except manual (so that would be aperture priority, shutter priority, program or any "scene" mode).

Here's how it works: exposure compensation starts set at "0.0".  All this means is that the camera will use whatever exposure settings the meter would normally come up with.  If you turn exposure compensation UP, i.e. set it to any positive value, the camera will automatically overexpose the image by that much.  "+1.0" will overexpose by a full stop, "+0.7" will overexpose by two thirds of a stop, etc.  On the other hand, if you turn exposure compensation DOWN, i.e. set it to any negative value, it will underexpose by that much.  "-2.0" would underexpose by two stops.  "-0.3" would underexpose by a third of a stop.  You get the idea.

So here's how you use exposure compensation.  Let's say you are taking a picture of a light-toned scene, say maybe snow or my light yellow dining room.  Since we now know how our camera's meter works, we know it will suggest exposure settings that would make the scene medium-toned (i.e. 50% gray).  To render our light-toned subject the way it actually looks, we will need to overexpose the image.  So, you just crank exposure up a stop or two ("+1.0" or "+2.0") and shoot.  Now hit play and check the results.  Two bright?  Crank it down a little.  Too dark?  Turn it up some more.

That's it.  It works for dark-toned objects too.  If you are taking a picture of your black desk, the meter is going to suggest exposure settings to make it gray.  If you want it to actually look black, turn exposure compensation down.  Check the results on the back of the camera, tweak the exposure comp and reshoot until you like what you're looking at.

THAT'S IT!  Its incredibly convenient, and fast, and easy to understand.  The more familiar you get with your camera's meter, the fewer times you will have to adjust and reshoot.  After a while, you will actually be able to predict how much or how little you need to over/under expose for a given scene.  It's also a great way to experiment with exposure.

Now, just for the hell of it, lets look at an example.  In this case the metered value (i.e. "0.0") was probably the closest to right, but you see how it works.  Exposure is somewhat subjective anyway, so maybe you like the one on the right better.  Click the image to enlarge for a better view.

Now I'll admit, the far right image is a little blurry due to camera shake, but you already know how to fix that, right?

Buying Your First SLR

Lets take a quick break from learning about exposure and talk about buying a camera.  The number one question I get from people is, "What camera should I buy?"


People who know a lot about photography looove to overcomplicate this question. While it's true that people have different needs and no single camera is right for everyone, its pretty easy to point someone in the right direction.

The fact is, if you're interested in taking up photography as a hobby and you ask me (or anyone else) what camera to buy, the unspoken part of that question is: "I don't know that much about photography yet, but I really want to learn.  I need a camera that will let me take pictures like the pros once I learn how to use it, and something I won't grow out of later on.  I also need something affordable since I'm just getting started and not 100% sure whether I'll stick with it or not.  What camera should I buy?"


The answer is: an entry-level DSLR kit.  DSLR stands for "digital single lens reflex" camera, just in case you were wondering.  What that means doesn't really matter, its honestly just trivia so I'm skipping it for now.  Also, when I say "kit" I mean it comes with a lens.  We'll get to that in a second though.

Ok, so there are basically 4 entry-level DSLRs on the market today that I would seriously consider:

1. The Nikon D3000
2. The Canon Rebel XS (or XSi)
3. The Sony Alpha A230
4. The Pentax K-x

In many ways they are very, very similar.  They all cost between $400 - $550.  They all have between 10 -12 megapixels (which is more than enough for anyone).  They all go up to at least ISO 1600.  They all have some form of vibration reduction which helps avoid "camera shake" at slow shutter speeds.  They all have maximum shutter speeds of 1/4000th of a second (which is fast enough for anyone).  They have all the exposure modes, metering modes and about every other type of setting or feature we will talk about.  You can take incredible pictures with any one of these cameras.

So how do you choose?

Well, as general consideration, try to think of this purchase as buying into a camera system, not just buying one particular camera.  The great thing about DSLR's is they have interchangeable accessories such as lenses, flashes, etc.  Once you start investing in a certain brand you're not just going to chuck all your old equipment and start over with another company.  You'll buy new lenses and accessories over time, and eventually when you're ready to upgrade or replace your current camera body, you'll buy a new camera of the same brand so it will be compatible with all your current lenses and accessories.

So what are these brands good at?  Nikon is famous for its lenses and accessories, while Canon is known for intuitive menus and great color rendering.  Pentax is a long-time maker of very popular entry-level SLRs aimed at students.  Sony has a lot of experience making image sensors and quality electronics in general.

Like I said above, these cameras have most of the same features and specifications in common, so here's a few reasons why you might choose one over the others.

Nikon D3000.  On paper it doesn't have anything the other cameras don't have, except a slightly larger LCD screen on the back.  However, it is a Nikon.  I know from experience that Nikon's 18-55mm lens is tack sharp, surprisingly holding its own against many of their more expensive products.  With this camera you're really buying into the Nikon system, and you basically have limitless room to grow with access to the best lenses and accessories in the business (OK, that's more of a personal opinion, but I'm not the only one who thinks so).  On the down side, it is the most expensive of the four cameras, but hey, you get what you pay for sometimes.

Canon Rebel XS.  Same specs as the Nikon on paper, and similar reasons to buy it.  You're buying into the Canon system, and as much as it pains me to admit, they have a huge variety of quality accessories also.  Canon also has very user friendly menus and, in my opinion, excellent color rendering.  I've seen these on sale recently for $500 with the lens included.

Sony Alpha A230.  Higher maximum ISO than the Nikon or Canon (3200 max instead of 1600).  That's a full stop, which honestly matters sometimes, and is a point in Sony's favor.  Also the cheapest of the group at $400.  I don't know if the build quality would be quite as good as the Nikon or Canon, and there aren't quite as many accessories available, but there's definitely everything you would reasonably ever expect to use.  If price is a serious concern, I'd pick this camera.

Pentax K-x.  Highest maximum ISO of all four cameras at a whopping 12,800 (that's 3 full stops above both the Canon and Nikon, 2 stops above the Sony)!  Also has HD video capability, and slightly higher resolution at 12 megapixels (all the others are 10).  It also one of the few cameras that still runs on AA batteries, which can sometimes be an advantage since they are available everywhere.  At $460 its in the middle of the pack on price.  The only disadvantage is doesn't appear to be self-cleaning like the other 3 cameras.

So what's my verdict?  If you don't have a brand preference, I would pick the Pentax K-x.  Its the most bang for your buck and has specs and features you'd expect in a much more expensive camera.  

However, if you really want to have unlimited room to grow, I might go Nikon or Canon.  The fact is they are the gold standards of the camera industry, and you know you are getting a quality product backed by decades of experience.  They have much larger lineups of cameras, lenses and accessories than either Sony or Pentax, and you're simply never going to outgrow their product lines.

If price is a big deal, and your wife or husband is sweating you about how much cash you're trying to blow on camera gear, pick up the Sony.  Its the most value-oriented choice, and you're not going to be missing out on anything, its still a fantastic camera.

Aaaaand DONE!  Is that enough info for you?  So now, go buy your camera, you kinda need one of those to learn photography!

Metering Mode pt. 2 - Center-Weighted and Spot Metering

OK, so yeah, I've been gone for a month.  Not out-of-town gone, more the wife-had-surgery-work-went-bananas-at-the-same-time type of gone.  But regardless, I'm back, and we need to continue our photo education, so lets get to it.

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In the last post we talked about matrix metering, which involves some pretty complex decision making on the part of the camera.  Now let's get into center-weighted and spot metering modes, which are much simpler and more predictable.

Center-weighted metering behaves the most like the classic "average luminance" metering we discussed in the first post on metering.  There is one difference however.  As implied by the name, center-weighted metering cares more about the center of the frame than the edges.  When I say the center, I mean a circle or oval taking up about 50-70% of the frame (the actual area being measured depends on your camera).  Center-weighted metering will suggest exposure settings that render this circle / oval area a medium gray, with some minor consideration given to very dark or very bright areas at the periphery of the frame.

There are two great thing about center-weighted metering:

1. It's predictable.
2. It prioritizes the center of the frame (where your subject tends to be located a lot of the time).

Center-weighted metering is good in situations where the center of the frame needs to be properly exposed and the edges don't matter.  For example, a portrait where the sun is setting right behind your subject, or a still-life shot of a leaf, sitting in a pool of light on the otherwise dark forest floor.  Makes sense right?

Now let's move on to spot metering.  Spot metering only measures a tiny portion of the frame (normally 2-5% of the total image area).  This spot is always in the center of the frame, although in some newer professional cameras it is possible to move the spot around.  Spot metering will suggest exposure settings that will make the object inside the spot appear a perfect 50% medium gray.

The two advantages of spot metering are:

1. It's almost perfectly predictable.
2. You can meter very small areas of the frame separately from each other.

Spot metering is good if you need a very precise meter reading for one tiny portion of the image and want to ignore everything else.  Now remember, when you spot meter an object it's going to give you exposure values that will make that object medium gray.  If you're spot metering a light-toned object you'll have to overexpose compared to the meter reading.  If you're spot metering a dark object, you'll need to underexpose it somewhat.  Spot metering also works great with auto-exposure lock, another feature we will come to shortly.

Metering Mode pt. 1 - Matrix Metering

OK, let's talk some more about metering. In the first post on metering, we oversimplified things a little too much. Don't worry, it's not really going to get more complex, but we need to refine the details a little.

We started with the understanding that your in-camera meter uses "average luminance" (i.e. brightness) to determine what exposure settings to use. That meant the camera's meter measured the total amount of light coming in through the lens, and assumed this light was spread perfectly evenly throughout the frame. The meter then suggested exposure settings that would make this average amount of light come out a medium gray tone in the final image.

This IS how light meters started out, however photography has come a long way and we now have more than one "metering mode" that controls how the meter behaves. There are basically three standard metering modes: matrix, center-weighted and spot.

"Matrix metering" is the smart(-ish) metering mode that is standard for almost all modern cameras. I'm going to use "matrix metering" in this post, but this is technically the Nikon term. I believe Canon calls it "evaluative metering" and the generic may be "zone metering", but I learned on Nikons and therefore I'm rolling with "matrix".

Matrix metering divides the frame into several different "zones" and measures the light in each zone separately. It uses this information to try and "guess" what kind of scene you are shooting and make exposure recommendations that would be best for this type of scene. Before this week that's basically all I knew about it, but thanks to Ken Rockwell's website (google him) I learned a bit more.

Let's use our old example of a snowy pasture to show how matrix metering works. Let's say our composition consists mostly of a snowy field, with a couple clumps of dark trees on the left side and the bright sun in the upper-right corner of the frame. Matrix metering is smart enough to know that there is nothing brighter than the sun that it can reasonably expect to run into. So when it measures something as bright as the sun in the frame (i.e. which is always the sun itself) it pays special attention to that. Matrix metering also knows that direct sunlight is very consistent and always produces the same amount of light. So now, matrix metering will pick exposure values that are suitable for subjects lit directly by the sun, and we will get realistic tones in our image that match what we see with our eye. The sun will be pure white, the snow will be a pretty bright white, and the dark trees will be black. Good job matrix metering!

Matrix metering has a lot of other logic included that helps it make good decisions. It is good at measuring the brightest and darkest areas of an image and trying to distribute these tones within the dynamic range of the camera. This means it tried to keep the brightest areas bright, and the darkest areas dark and strike a compromise somewhere in the middle. Here's a good example of it doing that:

See how it picked exposure settings that kept the dark areas from being pure black and the white areas from being pure white? It did a decent job of retaining detail in both these areas, and this looks reasonably like the scene did in real life (I know, a picture of the leg of my couch, how interesting).

That being said, as smart as matrix metering is, it is definitely not perfect and can be fooled. Let's go back to the snowy pasture example and pretend it is an overcast day instead. The meter is not going to see anything bright or dark enough to give it a good idea of what you are shooting. So it goes back to being a normal light meter. Most of the frame is snow, so it's going to make that medium toned (i.e. gray). If there are enough dark trees in the frame, its going to take them in consideration too and maybe pick slightly brighter exposure settings. In this case the snow may be a slightly lighter gray, but still not the white we are looking for. Sorry matrix metering, we know you tried.

Final thought: matrix metering is a good way to go most of the time for decent pictures. Its fairly smart and makes a lot of reasonable decisions. The problem is it still a machine, not a mind reader, and doesn't know your creative intent. Another problem is that it is not very predictable. If you are trying to over or underexpose something, its hard to know what the meter is already doing. Maybe it knows to overexpose the scene already (like the sunny snow day), or maybe it is hopelessly lost and shooting for a compromise (the cloudy snow day). If you are making your own adjustments, you have to guess how the meter already feels about this scene, which can be a mess.

That's the complex world of matrix metering, now let's move on to center-weighted and spot metering, which are much simpler!

A Quick Word About the Zone System

This is an afterthought to the last post on dynamic range, but let's take a quick look at the Zone System. This is something Ansel Adams and his buddy Fred Archer put together in the 1940's, originally designed for black and white film.

Basically they created their own 10-stop scale of tones from pure white to pure black (11 tones in all). This scale was supposed to represent the full range of black and white film and the paper it was ultimately printed on. Just to make things confusing, they labeled these zone "0" (zero) through "X" (roman numeral 10).

The idea was, the meter will always give you a reading for the middle gray tone "V" (5). Want to render whatever you just metered as zone "VII" (7, a light tone)? Overexpose by 2 stops. Want something to be zone "II" (2, a very dark tone), underexpose by 3 stops. Got it?

So why aren't we using the Zone System to talk about exposure? Well, first of all this scale represents the theoretical dynamic range of black and white sheet film, but all I care about the actual dynamic range of the digital camera I am using.

Second, I hate the numbering system. Roman numerals suck and are irritating to use. Also this doesn't match up to anything you see in modern cameras. Do I ever see a "VIII" or "IX" on my in-camera meter? No, I see "-2, -1, 0, +1, +2". Zero is metered value, not "V". Negative numbers are underexposure (darker), positive numbers are overexposure (brighter). That's pretty intuitive, right?

So that's why I more or less skipped the Zone System. This may make old school photography teachers want to cry, but I'm trying not to waste your life here. If you're shooting black and white sheet film and hand developing and printing it, learn the Zone System in depth, there are tons of books on it. If you're the other 99.99% of the population you can safely ignore it.

Tonality & Dynamic Range

In the last post, we discussed how your in-camera meter uses the average "luminance" (a.k.a. brightness) of a scene to suggest correct exposure settings. The problem we ran into was that the meter wants to treat everything like its medium gray. Its operating on the assumption that the light and dark areas in your scene fall neatly on either side of this "average luminance" and that this will be a good predictor for how you want your image exposed. However, not all scenes are average! The meter struggles with subjects that are supposed to be very light (snow) or very dark (a black cat). This is where we begin our discussion of tone.

Let's start by saying that your digital camera records two different types of information about light: luminance (amount of light) and color (you know what color is!). The camera takes the amount of light it receives (luminance) and renders this into different tones, that is, light or dark areas on the final image. Pure white, light gray, medium gray, dark gray, pure black, these are all examples of tones. We are ignoring color entirely here, for this post it doesn't matter if the medium gray was a medium red, green or blue, we're just talking about how light or dark this area is.

Now let's get down to brass tacks. If you are photographing something dominated by light tones (say a snowy pasture), you now know that the meter will suggest exposure values to make the scene medium toned (i.e. gray, dingy looking snow). Since we want bright white snow, we also know we have to overexpose this image compared to the meter's recommendation, but the question is, how much? 1 stop? 2? How do you know?

This is where dynamic range comes into the picture. Look at the picture below.

I took this series of test shots with my Nikon D200 for this post, to show the range of tones actually recorded by my camera. Slightly to right of center, you see the swatch of gray that says "0.0, 55%, metered value"? This is a piece of white typing paper shot at exactly the exposure settings recommended by the meter. It ended up being 55% gray (one would expect 50% gray, but hey, this is a real world test). This is a medium tone, which is what we should expect now that we know how the meter works.

In all of the swatches to the right, I overexposed according to the meter, first by one stop (+1.0), then two (+2.0), then three (+3.0). One stop overexposed brought me to 75% gray (a light tone), two stops produced 95% gray (almost white), and three stops overexposure gave me a featureless pure white.

Going to the left, one stop underexposure gave me a 35% gray, a fairly dark tone. Two stops underexposure created a 20% gray (even darker), three stops under was a 12% gray (pretty damn dark), four stops under equalled 5% gray (almost black) and five stops under exposed took me to 0% gray (pure black). By the way, I should probably be saying "0% lightness" instead of "0% gray", but you get the idea.

Did you notice something? It took only three stops OVER exposure to get to pure white, but five stops of UNDER exposure to get to pure black. Interesting huh? This range, from pure white to pure black, is called the "full range" of this camera, which happens to be approximately 9 full stops. On the other hand, the range from almost pure white to almost pure black (equivalent to 5% and 95% on the illustration above) is called the "dynamic range", which is approximately 7 full stops.

The important thing I learned from the above experiment was how much brighter or darker my camera makes an image with a one, two, or three stop adjustment from the metered value! We also learned that this is NOT linear, which is very useful. Intuitively you'd expect there to be a certain percent change in brightness for each full stop, say 20% brighter per stop. Go ahead and throw that idea out the window. Exposure isn't linear, its supposed to be logarithmic, but even that doesn't perfectly correspond to how a real camera works in a real situation. The important thing to know is how YOUR camera responds to changes in exposure, so you can create the kind of images YOU want!

To wrap things up, let's go back to our snowy pasture example. More specifically, let's say we are photographing one lonely sapling sticking up out of the snow. Almost the entire frame is filled with white snow, the thin black stick of the sapling is hardly contributing to the meter reading at all. So how much should I overexpose this? It depends. If I want a white, gleaming snow with no detail probably 2 stops, maybe even 1/3 or 2/3 stops higher than that. What if I want to really capture the texture in the snow itself but still render it a light tone? I'd probably go 1 stop over, or 1 and 1/3.

Ultimately I'd make some educated guesses, look at the photos on the back of the camera and at home on my monitor, and try to remember how I would have done it differently the next time I'm out shooting! The point is, it takes practice to learn how your camera renders different tones, and also how your meter evaluates different scenes. This post should give you a good starting point of what to expect so you don't have to feel overwhelmed. In the end your knowledge will always be fine tuned by experience, so go out and start experimenting!