Basic Exposure — The Four Camera Controls

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I wrote this back in 2008 for another website which no longer exists (in its original incarnation); I've finally gotten around to putting it here. There were originally some photos as examples which were lost; I'll recreate them and add them as I get opportunities.


There are four basic camera controls: ISO speed/sensitivity, Shutter Speed, Aperture and White Balance. Most cameras, even the bottom end ones, allow you access to at least some of those. Film cameras don't have white balance (the color balance is locked in by the manufacturer), but they do have the other three. The bottom tier (i.e. easiest) of cameras may allow you only limited options, but at least you have something to work with.

White balance is NOT part of exposure per se, but it's important so I'll give it its own section at the end.

The other three camera controls: Sensitivity, Shutter Speed and Aperture, all deal with exposure.

All FOUR controls affect image quality. Image quality and exposure are NOT the same thing. You can have an image that's beautifully exposed but blurry, or out of focus, or full of noise, or whatever.

For each camera control I'm going to discuss how it affects Exposure and how it affects Image Quality as separate issues.

A quick comment about the three controls which affect exposure: They are all interlocked. Think of exposure as being a Triangle where there are three equally weighted factors: Sensitivity, Shutter Speed and Aperture. If things are "balanced," as in you have a good exposure, then if you change ONE of those things, you have to change at least one other (or both) to bring it back into balance again.

The balancing act, and how each one affects the others, isn't difficult. It just takes some getting used to.

So first up we're going to discuss ISO speeds because that's the easiest one to understand.

ISO is typically called a speed, but really it's SENSITIVITY. It's how sensitive your film or your sensor is to light. The more sensitive, the less light you need to get something. Let's say that you're photographing a model's face. With something that's got a low ISO speed, you would need a lot more light than something with a high ISO speed to get the same result.

In your travels you may come across mentions of ASA speeds. ASA and ISO speeds are interchangable. The standards body that creates the standard and blesses the results changed, so the name changed. But ASA 100 is the same as ISO 100, and so on.

ISO speeds are given as whole numbers. Theoretically, and a century ago when film was not very sensitive to light, ISO speeds could be very low indeed. The original Kodachrome was ISO 10, then later ISO 25 (with a version that was ISO 64). On modern cameras, the lowest ISO you go is typically 100. If you buy film from a grocery or a department store, the slowest you can find is ISO 100. So for our purposes, we're going to start with ISO 100.

The higher the number, the "faster" the speed. That means the less light you need to get a given result. Thus, ISO 200 is faster than 100, and 400 is faster than both of those.

Modern cameras and film usually top off around 1600 or 3200. My Canon 40D goes up to 1600.

When film is created at the lab, it's "speed" is rated on the package. You buy a single speed of each roll you shoot, so you set your camera to whatever ISO speed the film says it is, and that's it. You forget it.

On digital cameras, however, you can play around with the ISO setting of your sensor (if your camera allows it). My camera, for instance, allows me to set it to 100, 200, 400, 800, 1600 or AUTO. Auto means that the camera sets the speed on its own, based on what it thinks is best. Most people leave their ISO settings to AUTO.

ISO Speed's Effect on Exposure
ISO speed is one point of the triangle, and if you change it, you affect the other two parts of the triangle. If you use a higher ISO speed, that means you need less light to get a result. Higher ISO means more sensitive.

ISO Speed's Effect on Image Quality
So you ask yourself, why not crank that sucker up all the way, then? If I can get results with less light, isn't that a good thing? Well, yes and no.

Think of ISO as SENSITIVITY, and think of it like a radio. You're listening to the radio and you pick up a weak station far away. It's very soft and there's a lot of static, so you turn the volume way up. It amplifies the sound of the station, but it also amplifies the static. The same thing for recordings: you amplify the hiss, hum, or other gremlin-made noises that are in the background.

On film, the higher the ISO, the larger the grain. Grain is the chemical structure that makes the image. When grain is small, the image looks smooth. When grain is big, the image looks like a sand-painting. The higher the ISO, the larger (in general) the grain.

On digital, ISO amplifies "noise," which shows up as kind of a gunky mottling of color. It's like getting a hard look at some people's skin in bright light: what looked smooth and even at a distance suddenly looks clumpy and uneven. The higher the ISO, the more the noise becomes apparent.

Here's are examples, taken this afternoon with my camera. It's not great but it does the job (I think it would be more obvious if I were shooting in dimmer light). One is called ISO 100 and the other is ISO 1600. Look at them side by side, and in particular, look at the clear part of the sky. The ISO 100 looks comparatively even and clean; the ISO 1600 has a mottling to it. You don't notice it so much on its own, but look at vs. the 100 side by side and it becomes apparent.

There are two schools of thought on how to set your ISO. School #1 says you should choose the lowest ISO you can get away with so you get the least noise. School #2 says you should use the highest you can get away with and still get good results, because the advantages (in most cases) oughtweigh the disadvantages.

Personally I tend to go for #1. I set the ISO as low as I can and still hand-hold my camera. If I have to go above 400, I start thinking about using a tripod or monopod. But I'm also a sharpness freak.

What you should do: If your camera allows you to set the ISO yourself: do it. Try photos at different ISO speeds and look at them. Determine the highest number you can use and still get good results.

So what do the numbers mean:
this is the hardest but it's still pretty easy, but you have to learn a concept in exposure called the STOP.

In photographic exposure, everything is about DOUBLES and HALVES. Remember Doubles and Halves. We double the amount of light, we halve the amount of light. Most steps up and down the scale in photography are done in Doubles and Halves.

ISO 100 is our base. It's the least sensitive. Imagine we were taking a photo of a gray wall and it took 1,200 units of light to expose properly (the picture looks the proper shade of gray): that's our baseline for this example.

ISO 200 is TWICE as sensitive as ISO 100. So for our above example, we would only need 600 units of light to get the same shade of gray recorded.

ISO 400 is TWICE as sensitive as ISO 200 (this is a geometric scale). It is, therefore, 4 times as sensitive as ISO 100. So at ISO 400, we only need 300 units of light to get our gray wall.

ISO 800 is TWICE as sensitive as ISO 400. That makes it 4 times as sensitive as ISO 200, and 8x as sensitive as ISO 100. We only need 150 units of light this time.

ISO 1600 is TWICE as sensitive as ISO 800, 4x as 800, 8x as 200, and 16x as ISO 100. We only need 75 units of light for our wall.

Do you see the progression here? Every time you double the number, you're doubling the sensitivity, or halving the amount of light you need to get the same result.

This works backward from 100 as well, if you're using slow film. ISO 50 is HALF as sensitive as ISO 100. ISO 25 is HALF as sensitive as 50, and 1/4th as sensitive as ISO 100.

Now you're going to learn a new word called a STOP. In photography, a STOP represents a doubling or halving of light.

ISO 200 is ONE STOP more sensitive than ISO 100. ISO 400 is TWO STOPS more sensitive than ISO 100. It is ONE STOP more sensitive than ISO 200. ISO 1600 is 4 stops more sensitive than ISO 100. It is three stops more sensitive than 200, two stops more sensitive than 400, and one stop more sensitive than 800.

The same works in reverse. ISO 25 is two stops slower than ISO 100. It is 6 stops slower than 1600. Count it out on your fingers if you don't believe me: 50, 100, 200, 400, 800, 1600. Six stops.

Remember the concept of stops, because we'll be applying it to both the other exposure controls. 1 stop is DOUBLE or HALF the light of whatever it's being compared against.

And that's the basics of ISO speed/sensitivity.

Shutter speed is easy because it's analogous to the real world—it's easy to visualize and think about. I think you'll find it the easiest one to use. It also pays off, since you can prevent some problems from occurring if you use the right shutter speed.

All film cameras have shutters. Many digital cameras have shutters, but some simply mimic the effect with the sensor.

A shutter is like a door. The door opens and closes completely. When it's open, light can strike the film or the digital sensor. When it's closed, light cannot reach it. So a shutter spends most of its time CLOSED.

A shutter's open time is measured in seconds. A shutter can be open for 1 second, say. That's called it's speed. On most cameras you can choose a shutter speed: a fast speed is a fraction of a second. A slow speed is longer.

Digital cameras without physical shutters can mimic this by simply reading the sensor for the length of time that the shutter is "open."

Film cameras typically have shutter speeds that run from around 1 second to 1/1000th of a second. Some can go longer or shorter, but that's the general spread. Digital cameras tend to top off around 1/4000th, but theoretically their longest time can be anything until the battery dies.

So imagine you're looking at a screen at an image projected from the outside world. The shutter is permanently open, so you can see movement as life goes by.

Imagine that the shutter is closed, but the flicks open for 1/1000th of a second, and the image on the screen is recorded. Because 1/1000th of a second is such a short time, you don't see movement on the screen. There was very little time for subjects to change. So you get a very "sharp" or still image.

Image you wipe it clean and do the same thing at 1/10th of a second. If you're shooting a still life, there's no movement and the image looks fine. But if you're shooting someone walking by, you'd get some subject blur, because the image was changing during that 1/10th of a second. The blur might not be much, but it's there. If you did the same thing at 1 full second, the blur would be more obvious. At 5 seconds it would be even more obvious.

The faster the shutter speed, the more it can freeze the action. So if you're shooting something that doesn't move—like the grand canyon, or someone sitting still, you can use a lower shutter speed. If you want to freeze action, like a dog jumping up to grab a frisbee, you want to use a fast shutter speed.

Subject Blur vs. Camera Shake
The example above, the dog jumping up to get a frisbee, or people walking by, is an example of subject blur, because it's the subject that's moving and creating blur. But there's also camera shake, which means the camera itself was moving when the image was taken. Usually you want to avoid camera blur as much as possible.

Camera blur most often happens when you're hand-holding the camera and the shutter speed is too slow. I've attached an example: I shot this Maneki Neko cat hand-holding the camera for 2 seconds. The Neko wasn't moving: the blur is my inability to hold the camera still for 2 seconds.

You can generally tell the difference between subject blur and camera shake by looking at the entire photo: subject blur is where only moving objects are blurry; camera shake makes *everything* blurry.

How to Determine Your Best Shutter Speed for Hand-Holding
The rule of thumb for 35mm cameras is that the slowest shutter speed to use is the same as the focal length of your lens. If you're using a 50mm lens, you can safely hand-hold down to 1/60th. If you're shooting at 200mm, you want to use 1/250th. With digital cameras, because focal lengths don't really translate the same, and because some cameras have Image Stabilization—all bets are off.

The best thing to do is to set your camera on manual, and shoot a series of photos at different speeds, then look at the results and see what's the slowest speed you're personally capable of hand-holding. If you have a zoom lens, you want to do this once with the zoom all the way out, again with it all the way in, and maybe another time with the zoom in the middle.

Shutter Speed's Effect on Image Quality
Determines the amount of image "blur" due to motion of either the camera or the subject.

Shutter Speed's Effect on Exposure
Shutter speed is one of the points on the triangle, so it directly affects the exposure of the image.

Shutter Speed Progression and Stops
So if you read the post on ISO speeds, you remember the part about Stops, and doubles and halves. Same thing happens with shutter speeds. On film cameras, shutter speeds always progress in doubles and halves, or 1-stop increments. 1/125th of a second, 1/250th of a second, 1/500th, 1/1000th, 1/2000th, etc. Going backward: 1/125th, 1/60th, 1/30th, 1/15th, 1/8th, 1/4th, 1/2, 1 full second. Doubles and halves.

I attached an image of the dial of a Nikon F4. Ignoring X, B and T, it runs from 1/8000th of a second to 4 full seconds, in 1-stop increments.

Digital cameras sometimes get complicated because they can choose shutter speeds "between" those I listed above. My Canon 40D is set to go in 1/2 stop increments, which means the progression would go 1/30th, 1/45, 1/60, 1/90, 1/125, 1/180, 1/250, 1/375, 1/500, 1/750, 1/1000 and so on. (A lot of rounding occurs). But you see the progression, right? Every doubling is 1 full stop.

You can connect this on the triangle directly to the ISO speed mentioned earlier. Let's say we're taking a photo of a cat and we like the result. The camera is set at f/8, 1/60th at ISO 100. f/8 is the aperture and we're going to leave that alone: for this example it will always be set at f/8.

Remember that ISO requires less light as the speed goes up, and it goes up in 1-stop increments. So if I raise the ISO to 200, I only need half the light, or 1-stop less light. So if I set the shutter speed to let in half the amount of light (1-stop less!), then I'll get the same result. So at ISO 200, the shutter speed of 1/125th will give me the same exposure that I got at ISO 100 with 1/60th

It will also be the same as 1/500th at ISO 400, or 1/1000th at ISO 800, or 1/2000th at ISO 1600.

You can see where cranking the ISO up becomes valuable. If you're taking photos of your kid breaking a board with his foot at karate class, and you want to freeze the action, you want a fast shutter. If the light isn't that bright, then using a high ISO will get you the shutter speed you need.

Shutter speeds work on fractions of a second, so you shouldn't have much trouble figuring out the difference between them. 1/30th of a second is twice as long as 1/60th of a second—it lets in twice as much light. There's TIME for twice as much light to pass. It's very intuitive.

A lot of cameras (both film and digital) have a semi-automatic mode called SHUTTER PRIORITY or Shutter Preferred. If you have that, you should switch to it and try it out. What Shutter Priority does is it lets you set the shutter speed and the camera will choose the aperture for you (and it should warn you if you want to use a shutter speed that won't get you a good exposure no matter which aperture the camera picks). So that's a good way to play around and see how it works: you choose the shutter speed, and the camera matches the proper aperture. (and yes, Aperture Priority does the same thing except in reverse. You choose the aperture, it picks the complimentary shutter speed).

I'm going to break this aperture thing into two parts because it's big. ISO is kind of straightforward and easy, and shutter speeds are common sense. But aperture is kind of like the knight in chess—it behaves completely differently than anything else around, and it's tougher to explain.

An aperture is a hole, or something that light can pass through. On 19th century cameras it used to be a hole that was bored into a metal plate and dropped in between lens elements. The hole was called a "stop," like valve stops in pipes. Later on, the holes were replaced with a diaphram of metal blades that can be turned so that the hole gets larger or smaller as needed. Your eye has a diaphram (the iris) which does the same thing: it's small when it's bright outside, and it's large when it's relatively dark. This diaphram is used as a way of regulating the amount of light that strikes the film.

ISO speed: the sensitivity of the film or sensor to light
Shutter speed: the amount of time that light is allowed to strike the film or sensor
Aperture: a restriction on the amount of light that can pass through the lens

Apertures are "sized" in f/numbers, more often called f/stops.

So What the Hell Do the Numbers Mean?
The f/stop is the ratio of the diameter of the aperture vs. the focal length of the lens.

That never really meant anything to me until my dad got a big Dobsonian telescope and the numbers were easy to understand. His telescope has an 8-inch primary mirror. There's nothing that further restricts the light, so in this case the aperture is the same as the diameter of the lens itself: 8-inches.

The mirror is ground so that the focal length is 64-inches.

64 divided by 8 is 8. So that's an f/8 telescope.

If he had the mirror re-ground to a focal lenth of 88 inches, he'd have an f/11 telescope. If the mirror were reground to a focal length of 32-inches, it would be an f/4 telescope. If he swapped out the mirror and got a 12-inch with a focal length of 64 inches, it would be f/5.3

Same thing happens with cameras, except you're usually dealing with milimeters instead of inches. If you have a lens that's 50mm focal length and the diameter of the aperture is 25mm, you're at f/2. If you made the diaphram smaller, say 12.5mm across, then you'd be at f/4. At 6.25mm you'd be at f/8. At 3.125mm in diameter, you'd be at f/16. And so on.

I think that's easy to understand, but if your eyes are glazing over, you want to remember that as the f/numbers get larger, the aperture gets smaller. f/22 is smaller than f/16, which is smaller than f/11, and all of them are much, much smaller than f/1.4

So Why Are We Using This F/Stop System Instead of Diameters And F*** the Math?
You talk about f/stops because it's a ratio that's independent of the physical size of the lens. As far as exposure is concerned, f/8 is f/8 is f/8. f/8 is the same on a Ansel Adams's Cooke Triple-Convertable Apalant lens as it is on a 50mm Nikkor camera lens, as it is on a cheap-shit Holga.

Imagine you're in a photographer's pool and you're all shooting a photo of the same thing. You're holding your Nikon D40, and Weegee's ghost is next to you holding a 1940 Speed Graphic with a 150mm Zeiss Planatar. He's getting good exposures. You ask him what he's shooting, and he says ISO 100, 1/125th at f/11. YOU could set your camera to ISO 100, 1/125th of a second at f/11, and get the same result.

That's why you can use one camera's light meter to set your own, or you can use a hand-held meter to set yours. Or use yours to set someone else's. F/stops are the same regardless of the lens you're using, because you're dealing with a RATIO, not actual, hard numbers.

All you really need to remember, though, is that low numbers mean BIG apertures, and high numbers mean SMALL apertures.

The 1-Stop Progression
It used to be real easy: some time in the early 20th century, camera and lens makers kind of standardized on certain f/stops. Basically they all agreed that f/11 was the main guy. f/11 shows up on nearly any lens you'll find.

So remember the thing about doubles and halves of amounts of light? And how 1 stop difference is DOUBLE or HALF something else? That there's a scale that you can go up and down like whole notes of music?

Here's the basic ISO scale again: 100, 200, 400, 800, 1600, 3200
Here's the basic shutter speed scale again: 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000

Here's the same thing for aperture: f/1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11, 16, 22

The difference between each one of those numbers is 1 full stop. The difference between f/11 and f/8 is 1 stop. The difference between f/11 and f/22 is 2 stops. And so on.

The Triangle is Complete
So now you have the third part of the triangle. Each scale has full stop differences, and a stop is a stop is a stop. So let's say you're shooting a photo of a dog running after a frisbee, and you start with this: ISO 100, f/8, 1/60th

You like the image—you think it looks good but the dog is blurry—you want to freeze the action. So you bump up the shutter speed 2 stops to 1/250th.

That means you're getting 2 stops LESS light than before. If you want to get the same exposure, you need to make it up somehow. You could bump up your ISO to ISO 400 (that's a 2-stop increase in sensitivity) and you'd be okay. OR you could open up your diaphram 2 stops to f/4. OR you could bump up your ISO 1 stop to ISO 200 AND open your diaphram up 1 stop to f/5.6. All of those would give you an equivalent exposure as what you'd started at.

Let's say your exposure is kind of dark and you decide you want to add 2 stops more light. You're starting with ISO 100, f/8, 1/60th. What do you do?

You could bump up your ISO speed two stops. Or you could slow down your shutter speed two stops. Or you could open up your aperture two stops. Or you could leave your ISO alone and slow your shutter speed 1 stop, and open your aperture 1 stop. Or some other combination that adds up to increasing your exposure 2 full stops.

But What's This Crapola On My Lens that Says It's f/3.5? Where's That On Your Scale?
It's not. You're right. That's an intermediate stop. f/3.5 is 1/3rd of a stop larger than f/4. A lot of cameras, like higher-end digitals, can be set to go in 1/3rd stop increments, rather than full stops. Some can go in 1/6th-stop increments. That doesn't change anything.

What Does the Front of My Lens Say?
The front (or side) of the lens should tell you the make and model, the focal length, and the LARGEST aperture the lens is capable of achieving. I've attached two examples. In Example 1, that's a Leitz Summicron, 50mm and the max aperture is f/2.

The second example is a Nikon 35mm-70mm zoom. It's max aperture is f/3.3 at 35mm, and f/4.5 at 70mm (because the focal length changes, the f/stop ratio changes!)

Okay, But I have a Zoom Lens that's Doesn't Change Its Max Aperture
Some high-end lenses have a max aperture that adjusts with the focal length so that the maximum aperture is the same at both zoom ends. Like a Sigma 70-210mm f/2.8 That's a maximum of f/2.8 at both ends.

Aperture size affects optical quality in two ways. One is the overall, general performance of the lens, and the other is about what appears in focus and what doesn't.

The first is fairly simple: we're talking about the general image as it's formed on the film or sensor. If you look at lens tests, just about every lens does its best work at the apertures in the middle of its range. That means if you have a lens that has an aperture range between f/3.5 and f/22, the lens will be sharpest and snappiest around f/8 or f/11. This is true at both the center of the image and the corners. As you work outward toward the extremes, the quality will fall off, particularly in the corners.

Will you notice the difference? Depends on how critical you are, whether you blow your images up high, and how good the lens is to begin with. But the point is this: if you're out and about and you have the luxury of choosing any aperture you want to use without any other concern—choose something in the middle of your camera's range, like f/11.

Now the focus part. This is kind of involved.

DEPTH OF FIELD
There's a concept in photography called Depth of Field. The "field" is what appears to be in focus. The "depth" part means your line of sight straight out from the lens. If one thing appears sharp and everything before and behind it looks blurry, that's a shallow DOF. If everything looks sharp at the same time, that's deep (or long) DOF.

I was thinking about this as I was driving home today. The guy ahead of me was about 8 car lengths and he was in focus. I *knew* that the instruments on my dashboard were out of focus, but it doesn't seem that way because my eyes can shift focus so rapidly that everything *seems* to be sharp everywhere at the same time. It's not—but it seems that way.

The camera can't do that. It can only focus on one thing at a time, so some things are going to be sharp (what you're focused on) and other things are going to be less sharp, or blurry.

Big apertures (small numbers) give you the shallowest DOF. Small aperture (big numbers) give you the largest DOF. So you can, to some extent, control what's sharp and what's blurry by selecting the aperture on your camera.

Here's an example.
Image you're on a beach in France. Far, far away there's blue sky, a few fluffy white clouds, sand and surf. In the middle distance (say about 20 feet away) is your wife (or husband, Jaques the cabana boy if you want). In the foreground, hidden from your wife behind an umbrella but fully visible to you, about 6 feet away, is Scarlet Johansson's body double, topless, and she enjoys being photographed by guys who will keep these photos in deep recesses on their hard drive where they'll never been seen by anyone but You and maybe a couple of your closest horndog friends.

First, we'll focus on the clouds way to hell and gone in the distance. We'll set our lens wide open to f/1.8, which is maximum on the lens we're using today. What do you see? The clouds and the distance appears sharp. Wifey looks blurry, and Scarlet is nothing but a haze.

Now we close the aperture (called stopping-down) to f/5.6, which is a middling size. The sky is sharp. Wifey looks soft but not bad. Scarlot is mostly a blob. This is the one you'll print out for Wifey later on.

Now we stop down to f/22, which is the smallest this lens can go. The sky is sharp. Wifey looks in focus. Scarlet's kind of soft but not bad.

Next: we refocus. This time on Wifey, who's in the middle distance, and we'll open back up to f/1.8.
At f/1.8, wifey is sharp, Scarlet and the background are both very blurry.
At f/5.6, wifey is sharp, Scarlet is fuzzy but recognizable, and the background looks pretty good.
At f/22, wifey is sharp, Scarlet is acceptable, and the background is sharp

Finally we refocus, this time on Come In Tokyo.
at f/1.8, Scarlet is sharp. Wifey is kind of a blob. The background is just a fog.
at f/5.6 Scarlet is sharp, Wifey is kind of soft but acceptable, the background looks good
at f/22, Scarlet is sharp, Wifey is sharp, background looks good

Large apertures tend to isolate what you've focused on from the background. Small apertures tend to render everything sharply.

In the 30s there used to be a group called f/64, and they were sharpness fanatics. They believed everything should be tack sharp from one end of the photo to the other, corner to corner, foreground to background. At f/64, you tend to be able to do that sort of thing.

You Can Bail Out Now If You Want To

but I'm going to add a couple of small kinks to what I've laid about above.

1. Imagine your depth of field as being like a rectangle with the long sides drawing away from you. You'd think your focal point would be in the center of the rectangle, and you'd have equal area of DOF in front of and behind your subject. Nope. Push your imaginary rectangle back so that your subject stands about 1/3rd back from the front edge. In other words, on any thing that you focus on, no matter how you set your aperture, the area that's in focus in front of your subject will be less than what's behind it.

2. The size of the rectangle also changes with how far away you're focused. If your subject is nearby, the rectangle will be relatively smaller than if your subject were farther away.

I'm going to make up the numbers, but this will illustrate what I've said:

Imagine you're shooting a photo of a model. The model is 6 feet away, and you're focused on her eyes.
At f/1.8, you can get a sharp image of anything up to 1 foot in front of her and 4 feet behind her
at f/5.6, you can get a sharp image of anyting up to 2 feet in front of her and 8 feet behind her
at f/22 you can get a sharp image of anyting up to 3 feet in front of her and 20 feet behind her

Now you move the model back to about 20 feet away and you focus on her eyes.
At f/1.8, you can get a sharp image of anything up to 3 feet in front of her and 10 feet behind her
at f/5.6, you can get a sharp image of anyting up to 5 feet in front of her and 20 feet behind her
at f/22 you can get a sharp image of anyting up to 10 feet in front of her and 50 feet behind her

Finally you move the model back to about 50 feet away and you focus on her eyes.
At f/1.8, you can get a sharp image of anything up to 5 feet in front of her and 40 feet behind her
at f/5.6, you can get a sharp image of anyting up to 10 feet in front of her and everything behind her
at f/22 you can get a sharp image of anyting up to 25 feet in front of her and everything behind her

So What's the Bottom Line?

If you want as much as you can see to be in focus as possible, focus on something relatively distant (like 30 feet) and use the smallest aperture you can.

If you want to isolate your subject from the foreground and background, use the largest aperture you can, and try to get the subject as close to the camera as you reasonably can.

Aperture Priority

In the part where I talked about shutter speeds, I said there was a semi-automatic mode on many cameras called Shutter Priority, where you tell the camera which shutter speed to use and it picks the aperture. APERTURE PRIORITY is the same thing in reverse: you pick the aperture and the camera picks the shutter speed. If you want to play around with aperture settings, try out Aperture Priority. It allows you the freedom to experiment, but lets the camera do the dirty work of figuring out the proper exposure.

White balance is the last of the major camera controls.

Imagine a thing called a Black Box. It's black—it reflects and emits no light whatsoever when it's cold (absolute 0-deg).

Now you begin to heat it, and as it warms up, it begins to emit light. The temperature is measured in Kelvin, which is identical to Celsius except that Kelvin begins counting from absolute zero (around -473 deg C). If you take the Celsius temperature and add 473, you'll get the equivalent Kelvin number.

Around 1000K (you usually don't see the degree symbol when you're looking at kelvin numbers) the box is a deep red. As you continue to heat it up, it gets brighter red, then orange, then (for our purposes) looks pretty white around 5000K. Then it starts to tint blue, then very blue, then deep, dark blue. By 20,000K it's indigo blue.

Real-world light sources (with a few exceptions) emit light that can be measured in degrees Kelvin, and the color temperature matches what we got off that black box. A standard household light bulb, for instance, is around 2500K. Tungsten lamps that are often used photography or theater lighting are around 3200K or 3400K. Bright sunlight, under normal conditions, is around 5500K. The electronic flash on your camera is usually around 5000 to 5500K, depending on what the manufacturer thought was best. Skylight, where the sun is not directly shining on something (i.e. you're in shade) is above 10,000K.

Here's an interesting chart that shows some color temp scales.Light Bulbs Direct.

A person's brain automatically balances the light you see. You look at something you know should be white, and if it appears pale blue—a minute later your brain will adjust everything and it will look white. Have you ever been indoors in the late afternoon when the lights are on, and everything looks normal? You look out a window and everything outside looks deep blue. You walk outside and after a few minutes, everything looks normal, but you look back through the window inside the house and everything is yellow-ish red. That's your eyes adjusting the color balance.

Film and digital sensors can't do that. Film comes from the factory "balanced" for a particular temperature. "Daylight" film thinks "white" is 5500K, which makes things look normal when you shoot in broad daylight or with flash. But if you shoot indoors without flash, everything looks red. "Tungsten" film looks normal indoors if you use tungsten lights, and only a little bit red if you shoot indoors without a flash: but it looks very blue if you shoot it outdoors under sunlight or with a camera flash.

For film cameras, you can correct this with optical filters. You find out (as well as you can) what color temperature the lights are and then select the proper filter(s) to correct it for the type of film you're using.

Digitals are way easier: you can correct it electronically. Most cameras have an "auto" setting, where the camera takes a reading and tries to guess what the color temperature is, and then it adjusts accordingly. This doesn't work very well. If you can, you really ought to experiment with setting the white balance yourself.

Even the low-end point-in-shoots usually have a few preset options for white balance. There's usually an "sun" setting, which is around 5500K, an "indoor" version, which is around 3000K, maybe a "shade" version which is around 10,000K, maybe a "flourescent," which is another thing entirely (I'll discuss this below).

More advanced cameras usually offer the ability to manually set the exact color temperature, which means you can tell it you want 4120K if you feel like it. Many also have a "custom" balance, where you photograph something that you know is white, and that tells the camera, "adjust this so it looks white."

If you do the custom route, you want to buy a standard white card or gray card from the camera store, because the color is printed specifically to reflect properly and won't mislead your camera. You can try it with other things, like a page of blank printer paper, but I can't guarantee it'll work properly. (I use a gray card)

Regardless, what you want to do is this. When you want to take a photo, be aware of your surroundings. If you're outdoors in bright sun, set your camera to daylight. If you're photographing someone or something that's illuminated only by the sky, try the Shade option. If you're indoors using flash, use the Flash setting (if you have one). If you're not using flash, use one of the indoor settings.

Take some test photos (this is the beauty of digital) and see how they look. If they're too red, choose a setting that's got a higher color temp, because that will cool it down. If it's too blue, warm it up by lowering the temperature. This is particularly easy if you can directly choose a color temp: i.e. in you're indoors and you're shooting by candle-light w/o flash. You start by setting the camera directly to 2000K. The image is too warm. You drop it to 1800K. Too cool. You move it to 1900K. That looks good.

You can do special effects this way. You want your photo to look particularly warm? Shooting someone at the beach and you want to fake the glow of a sunset? Raise the color temp on the camera and things will look "warmer." In the snow and you want things to look colder? Lower the color balance and you'll have a blue cast that will make the image look cool. A small amount is discreet, a large amount is obvious.

The thing about color balance is that's hard to fix it after the fact in Photoshop—it's better to try to get it right (or at least close) when you're taking the photo, and then you can play around with it in Photoshop later. So I always highly recommend that people turn the auto white balance OFF and play around with the options and learn how to do it manually. That way you get what you want.

Flourescent

Floursescent lights are proof that there is a Devil and he is walks the earth. Among other things. flourescents don't behave the same way as most other lights do in terms of color. Typically they throw a funky green cast that makes things look sea-sick green. If your camera has a Flourescent setting, try it whenever you're indoors with flourescent lights. If you shoot film, you might want a flourescent filter.

Another problem is that flourescents don't behave the same way from one to the next. Different manufacturers and types all throw different colors, so your flourescent filter or digital camera setting won't necessary work properly even though the light source is flourescent. The old standard bulbs are green, but some manufacturers sell tubes that have more pleasing color. If you know what kind of tube it is, you can usually Google it on the net and somewhere you'll find the color temperature and/or how to correct the color for it. But most people have no idea what type of tube they're using, and nobody wants to find out.

My advice is, again, take test shots. Shoot with the flourescent setting (if you have one) or filter and see how they look. Usually they're on the cool side, so if you want to bias things, try a color temperature around 6500K and see how it looks. Also be prepared to subtract green when you're in Photoshop.


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©opyright by James Ollinger. All rights reserved.