Exposure Basics

The next thing I will cover is

Exposure


If you're just starting out in photography, you may not understand what exactly this means. I'm going to try to cover this with a lot of detail, yet keep it as simple as I can! :)

Basically, exposure is how long your sensor (or film) is EXPOSED to the light coming in through the lens (TTL). Your exposure will control how light or dark your shot will be. Simple, right?

Not exactly... There's a lot that goes into getting the proper exposure. If you don't understand how to read the meter in your camera, you won't have much success getting proper exposures. So, let's try and figure that meter out!

This is what you will see looking through your viewfinder:

metering.jpg

Your meter may be flipped in the other direction, but the reasoning remains the same. 

So, how do you use this thing?! I know it looks confusing, but bear with me.

Basically what you want to do to get a proper exposure is get your shot within the "Proper Exposure" bars I have listed above. Easy right? If you are towards the "+" side of the meter, you will be OVER exposed. This means your sensor has been EXPOSED too long to the light, and the resulting image will be brighter than an optimum exposure. Go too far to the "-" side of the meter and the opposite will happen. Your photo will be too dark. You want to aim for the center. Simple! But wait.... There's more...

So now you understand what you're aiming for, right? Aim for the center. But, what if you're aiming for the center and your photo still isn't coming out properly? What if it's still coming out too dark or too light? This is where METERING comes in.

Your camera is more than likely capable of 3 separate metering modes: Spot metering, Center Weighted Metering, and Matrix Metering. Here is what they look like:

spotmeter.jpg

SPOT METERING

centerweighted.jpg

CENTER WEIGHTED METERING

matrix.jpg

MATRIX METERING

If you look at them, you can tell what they are going to do for you. Basically you are telling the meter where you want it to set your exposure from. If you want to expose for a whole scene, you will want to use the MATRIX metering mode. If you want to expose for the center of the scene, you will use the CENTER WEIGHTED metering mode. Finally, if you want to measure for a single spot.... yeah... SPOT metering.

Pretty easy, huh?

Why do they have separate metering modes? What difference does it make?! Let me show you.

Say you have a scene that is backlight by the sun. Example here:

exposure1.jpg

This is where those metering modes come into play. Nice brightly lit backgrounds can be pretty tough to meter for, so going into the scene, you need to know which way you'll be metering. What do you think you would use here?

Spot metering would be the right choice here. Why? Because if you think about it, you aren't trying to expose for the entire scene here. You're trying to expose for your subject. In this case, these two in the photo. Let me show you what it would look like if I used MATRIX METERING here:

exposure2.jpg

Why do you think that happened?

The meter is trying to give you the proper exposure for the entire shot. If it has to meter the sun behind your subject, it's going to tell you to under expose your subject in order to get the OVERALL exposure to an accurate exposure. 

Hopefully that gives you an idea of the light meter. If not, go back through it, then go take some test shots and play around with the settings. You'll get it soon enough! 

I went over the light meter before this next part because I feel you should understand how to adjust your exposure before you learn what you're actually changing. Enter the EXPOSURE TRIANGLE!

Untitled-1.jpg

Yeah, it is a little confusing, huh? We'll get there, I promise!

The exposure triangle covers the 3 elements of exposure: Aperture, Shutter Speed, and ISO.

Each one will affect your exposure in a different way, and it is IMPERATIVE you understand how.

Let's start with your aperture. 

Aperture is controlled by the front dial on the camera (in front of the shutter release button on most every DSLR). Turn it one way, aperture goes up. Turn it the other way, aperture goes down. Easy. But what IS aperture?

Aperture controls the AMOUNT of light that is allowed to hit the sensor. Measured in F-stops indicating the size of the opening of the blades, the lower the f number, the more light you let in. Higher numbers let less light in. 

So, when your meter is reading under exposed, you're set at aperture value f/7.1, what could you do with your aperture to expose properly? 

You could raise your aperture! Maybe try f/5.6 or f/4. Just keep dialing until your meter reads 0 like the diagram above.

So what if you did that? What if you reached your lens's largest aperture (the lowest number) and it's still reading under exposed. Well, that's why it's called the exposure TRIANGLE. We're going to have to adjust something else.

Just a side note, it is wise to adjust ONE part of the triangle at a time. We'll get into this more later, but I want to make sure I get this in. If you adjust all three at once, it will be tough to get a correct exposure.

Let's try adjusting the SHUTTER SPEED.

The shutter speed is the length of time your shutter is open allowing light to pass through to the sensor.

The longer the shutter is open, the more light will hit the sensor. More light means a brighter image. Conversely, the shorter the shutter speed, the less light will hit the sensor. Less light, darker shot. Easy as that.

Here's the trick though... your aperture and shutter speed affect more than just those key aspects of exposure. 

Your aperture also controls the DEPTH OF FIELD or the section of your shot that will be in focus. To get a larger depth of field, you will want a smaller aperture (larger number). If you want a smaller depth of field, you're going to want a larger aperture (smaller number). Smaller depths of field are nice to get blown out backgrounds like this:

15.jpg

See how the background is blown out? If you want shots like this, you will want to invest in fast glass. Aperture values of f/1.2 on the ultra fast end to about f/4 which is still fast enough to get a shallow depth of field. BTW - We call this "fast glass" because, using the exposure triangle, if we are able to raise our aperture to let tons of light in, we are able to then raise our shutter speed to "faster" speeds and still get proper exosures.

What is the benefit of that? Isn't 1/40 of a second like LIGHT SPEED? 

Yes, it's super fast! But not to photographers!

You will learn soon enough that you will not be able to freeze motion in low-light conditions. You'll also learn that low-light means an average room in your house with the lights on at night... but we'll get there later.

This is where the fast lenses come in handy. Say you're still dealing with a situation like the one above... you've raised your aperture to its max value, now you have to adjust something else. Shutter speed. So now we raise our shutter speed so our meter reads 0 for a correct exposure.

Now our exposure is finally correct and the shot is going to be perfect! Ehh, not yet. Your subject is moving a little. Maybe its a flower you're shooting and it's moving in the breeze. That 1/40 of a second isn't going to cut it! Remember this is a triangle though... Enter ISO.

ISO controls the sensor's SENSITIVITY to light. The lower your ISO is set, the less sensitive the sensor is to light. The higher the ISO, the higher the sensitivity. This is a fairly simple concept so let's apply it to our shooting scenario.

These are our settings at the moment... Our aperture is set to a fairly fast f/4, shutter speed set to 1/40 of a second and our ISO set to most camera's base setting of ISO 100. 

I mentioned before our subject is moving. 1/40 of a second just isn't fast enough to freeze that motion and get a nice, crisp, accurately exposed shot.

What do we do here? We've maxed out 2 of the 3 aspects of our triangle.

We're going to be raising our ISO, our sensor's SENSITIVITY to the light coming in.

The downfall of raising ISO is that with all that sensitivity, you are introducing noise and grain into the image. Lower end cameras don't handle ISO increases that well, so this should be the last thing you change if you're using a lower end model. 

Let me be clear however, GRAIN is not a bad thing. You can still have a great shot and have grain at the same time. Let me show you:

DSC_1423.jpg

Say we raise our ISO to 400. That is 2 total stops of light we shifted up. I'll get into 'f-stops' in another tutorial, in-depth, but a short explanation is an f-stop increase doubles your light reaching the sensor. 

Here's an example:

You're at ISO 100 and you shift up to 200. You doubled your ISO, therefore you doubled your light. What would one more stop up be? 

ISO 400. See how that is a total of 2 stops up?

Anyway, in our situation our settings are now f/4 1/40 and ISO 400.

Since our exposure was properly set before we bumped the ISO, now we will be over exposed by 2 stops because we raised the sensitivity by 2 stops. Your shutter speeds also work in 'stops'. Double the speed to increase a stop exactly like ISO. 

So we're at 1/40 of a second. Let's go up 1 stop to 1/80 of a second. Up one more to 1/160 of a second. This will now give us a proper exposure, only this time we have a shutter speed of 1/160!

THAT will freeze the flower for us!

The triangle all works together. If something goes up 1 stop, something has to come down 1 stop to give you the same exposure.

Keep toying with it and you will end up getting it. Just like anything, the more you do it, the better you will get! Don't give up!