Wednesday, May 2, 2012

Camera 101: Basic Controls and Exposure

This is the first in a series of tutorials designed to teach you more about taking photos with a DSLR.

We're going to start off with a basic overview of the controls on your camera.  I'm going to use the very popular Canon T3i, but if you have a different camera don't worry - the basic controls are pretty similar from one camera to another.

What you can control

Before we have a look at how to control your camera though, let's first have a very quick look at what you can control.  I'll be going into all of these controls in greater detail in future articles:

Shutter Speed

Your camera has a "shutter", which opens for a short time to let light fall on your sensor.  You control how long it's open for (and therefore control how much light gets in) using the shutter speed.  This is typically measured in fractions of a second (e.g. 1/200th of a second) although you can set this to long values (e.g. 5 seconds, usually shown as 5".)

A longer shutter speed lets in more light, and a shorter shutter speed lets in less light.  Obviously, a 1/2 second shutter speed lets in half as much light as a 1 second shutter speed, because 1/2 a second is half as long as 1 second.

A fast moving object will have some motion blur with a long shutter speed, whereas a short shutter speed freezes motion.

Aperture

The aperture is a circular iris, much like the iris of your eye. The aperture, like the shutter, can also be used to control how much light makes it to your sensor; open the aperture all the way, and a lot of light will get in.  Close it down tight, and less light will get in.  Also, a wide-open aperture will create a very shallow "depth of field", whereas a tight one will create a large "depth of field."  We'll talk more about depth of field in another article.

Aperture is measured using a value called the "f-number", usually written as "f/3.5" or "f/8".  Note that the "f/" makes it look a bit like a fraction.  That's because it is!  Just like a shutter speed 1/30th of a second lets in less light that 1/15th of a second, an aperture of f/8 lets in less light than f/5.6.  The higher the "number" the more tightly closed the aperture, and the less light you get.  Some cameras will display this without the "/" or even without the "f" but don't let that fool you - it's still a fraction.

The other thing to know about aperture is that is not a linear scale.  f/1.4 lets in twice as much light as f/2, which lets in twice as much light as f/2.8.  (If you're curious, you let in twice as much light every time you multiply by the square root of two, but the details are for another day.)

ISO

The ISO number is a measure of how sensitive the sensor in your camera is to light.  At ISO 200, your camera is twice as sensitive to light as ISO 100.  A higher ISO will let you take the same shot with less light in the room.  As usual in this world, you don't get a free lunch; a higher ISO will also result in an image with more noise.

Read more after the jump!

Exposure

Your camera probably has a lot of other controls, but these are the most important ones.  These are the ones that control your "exposure".  Exposure is the art of getting the correct amount of light through the lens and onto you sensor.  Too little light, and the photo will come out "under exposed".  Too much, and it will be over exposed.


If you under expose an image enough, it will actually come out black.  Over expose it, and it will come out white.

If you halve the shutter speed, you let in twice as much light.  If you open the aperture from 1.4 to 2, or from 2 to 2.8, you let in twice as much light.  If you double your ISO, you make the sensor twice as sensitive to light (which is just as good as letting in twice as much light.)  Since all of these controls do something similar, we have a common name for all of them: letting in twice as much light is called "going up one stop", and letting in half as much light is called "going down one stop."

How you control it

Alright, it's time for an exercise.  Go get your camera.  Take your time, I'll wait.

Ok, got it?  Excellent!  If you're using the Canon Rebel T3i (or the Canon 600D) it will look like the photos below.  If you're using some other DSLR, don't worry, as the camera will look very similar.  If you have trouble, post a question in the comments below, with the make and model of your camera, and I'll do my best to help out.
Image from 600d

Image from 600d


Turn your camera on, set the mode dial to "M" (this is manual mode, where you control everything.)  Now, look through the viewfinder, and push the shutter release button halfway down (not all the way down - if the viewfinder turns black for a moment, that means you went too far, and you just took a picture.)

You should see a bunch of stuff light up at the bottom of the viewfinder.  If you have the Rebel T3i it will look like this:


Note that part down there at the bottom, the "exposure meter".  There's a vertical bar at the bottom of the exposure meter, and most of the time, you want that indicator right on the zero.  If you take a photo with the triangle to the left of 0, your photo will (most of the time) turn out under exposed, to the right, over exposed.

If you don't do anything for a little while, the viewfinder display will disappear to conserve battery.  Just push the shutter halfway down to wake it up again.

Most important controls on your camera are controlled by the main dial.  If you have a fancier camera, such as the Canon 7D or the Canon 5D Mark iii, then your camera may have two dials (on Canon cameras, the second dial is usually on the back, around the "Set" button.)

The first thing we're going to do is set the ISO.  Press the ISO button (on top of the camera for the T3i/600D, but sometimes it's on the back of the camera.)  It's easiest to set the ISO on the screen, but on most Canon cameras you can also use the ISO display in the viewfinder, and turn the main dial set the value.  Turn the dial until the ISO reads "800", and then press "Set".

Now that we're out of "set ISO mode", turn the main dial to adjust the shutter speed (yup - the very same dial you were just turning to set the ISO.)  If the triangle in the exposure meter is at the very far right, you want to adjust your shutter speed to a faster value (so if you're at 1/10th of a second, try going to 1/60th of a second).  If it's at the very far left, you want to go to a slower shutter speed (from 1/60th, for example, down to 1/10th.)  Try and get the triangle to the middle.

Once it's in the middle try adjusting the shutter speed, and see what happens.  Notice that if you double your shutter speed (from 1/100 to 1/200, for example) then the indicator will move from 0 to -1.  This is your camera telling you that it thinks your photo is going to come out under-exposed by one stop.  You can fix this by halving the shutter speed, by adjusting the aperture to a lower f-number, or by upping the ISO.

Try pointing your camera at a bright light.  Notice how the meter moves to the left - your camera is telling you that this scene is brightly lit, so you need to adjust your controls to let in less light.

Now we're going to change the aperture.  On the T3i/600D, you do this by holding down the "Exposure Compensation/Aperture" button, which has "Av" and a white/black "+/-" on it.    If you have a two-dial camera, turning the second dial will adjust the aperture.  Starting with the exposure meter in the middle, try changing the aperture.  Note that higher f-numbers result in the exposure meter wandering off to the left, and lower f-numbers go right.

Finally, we're going to go back to the ISO, just like we did before.  Try adjusting the ISO; going to a lower ISO will move the exposure meter left, and a higher ISO will move it right.  Notice that doubling the ISO will go up one stop on the exposure meter, and halving the ISO will go down one stop.

Wander around your house, and take some photos in manual mode.  Now, go outside and do the same.  Try to keep the exposure meter in the center to get correctly exposed photos.

If you find yourself in a very dark environment, you'll want to set your aperture as wide as possible (lowest f-number).  This is called "shooting wide open."  Then you'll want to set you ISO as high as you can (or as high as you're willing to go - a very high ISO will produce a lot of noise in your photo, especially in an under-lit scene.)  Then finally, you'll want to set the shutter speed to correctly expose the scene.

If you're outside on a brightly lit day, then you have lots of light to work with, so start by setting your ISO to the lowest value you can (usually 100) to get the sharpest, least noisy images possible.  Then set your aperture and shutter speed to taste.

When not to trust the exposure meter

The exposure meter is based on how bright and dark various parts of the scene are.  Your camera can't think; it has no way to tell the difference between a properly lit grey wall, a dimly lit white wall, or a very brightly lit dark-grey wall.  As a result, if you're looking at a scene with a lot of white in it (children playing in a snowy field, for example) you have to shoot with the exposure meter on the right-hand-side of 0.  The camera might think the photo is going to come out over-exposed, but it's wrong.  Use the LCD to judge (or the histogram, if your camera has one.)

Similarly a dark scene, such as someone dressed all in black in a dark alley will need to be shot with the exposure meter on the left hand side of 0.

Note that I take no responsibility if you get mugged while trying to take photos of shadowy figures in dark alleys.

Putting it all together

It might seem strange that there are so many different controls that adjust how much light comes into the camera, but remember - the primary purpose of a camera is to capture light and record it.  The "photo" in "photograph" comes from "photon".  Also, as we very briefly touched on earlier in this article, all these controls also do other things too - a fast shutter speed freezes motion, but if you want a fast shutter speed, that means you're cutting down on the light coming into the camera, so you need to make up for it with ISO or aperture.

If you found this helpful and you'd like to see more articles like this in the future, please like this post, or leave a comment below!

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