Exposed!

In my previous posts, I’ve gone over aperture and shutter speed.

Hopefully those two concepts are pretty clear now. If not, here's a quick refresher on aperture:

• Aperture indicates how wide your lens is open and how much light it lets in.
• Aperture is measured in f-stops.
• Small f numbers gives you a wide aperture.
• Large f numbers gives you a narrow aperture.
• Aperture also controls depth of field.
• A wide aperture gives you a shallow depth of field.
• Narrow aperture gives you a wide depth of field.

And here’s the rundown for shutter speed:

• Shutter speed lets you control how long the shutter stays open and how much light hits the camera's sensor.
• Shutter speeds are measured in seconds and fractions of seconds.
• A shutter speed of 1/250th of a second appears as 250, while 20 seconds appears as 20".
• Changing shutter speed allows you to freeze and blur motion.
• A fast shutter speed freezes motion.
• A slow shutter speed blurs motion.

While playing around with the aperture and shutter speed on your camera, you may have noticed that there are four modes on your digital SLR control dial in addition to the “AUTO” and scene modes. These modes are Program (P), Shutter Priority (S or Tv), Aperture Priority (A or Av) and Manual (M).

Program mode is very similar to auto mode, except that you have the ability to adjust certain camera settings like ISO, white balance and metering (more on these in later lessons). The important point is that in program mode the camera is selecting BOTH an aperture and a shutter speed for each photo you take.

In shutter priority mode, you control the shutter speed, and the camera picks a matching aperture to get a good exposure. In aperture priority mode, you control the aperture, and the camera picks a matching shutter speed to get a good exposure.

So what's manual mode good for?

This is going to be answered over the next several posts.

So for this particular post I want to go over some new definitions and also expand some of the older ones before going into further details about exposure.

Aperture and Shutter Speed Revisited

Aperture controls the amount of light that enters the camera and so does shutter speed. Seems like there might be a relationship here right?

So imagine that you're inside a building at night. You're standing in a hallway that's lit, and you'd like to find out what's behind a door. The light is off in the room behind the door, so you'll have to see into it using light from the hallway.

You have two ways of approaching this:

1. Crack the door and hold it open for a long time until your eyes adjust to the dim light in the room.
2. Pull the door wide open for a short period of time to let all the light from the hallway fall into the room.

Either way, you are letting the same amount of light into the room.

For you people who enjoy math, this pretty much sums it up:

Narrow opening + Long time = Wide opening + Short time

Aperture represents how wide the door opens and shutter speed is how long it stays open. This means that there are always two ways for you to take the exact same photo (more on this next time).

Exposure

Normally, you would want your photographs to be correctly exposed. So let's go back to the example with the door in the hallway. If you open the door wide enough and long enough, you'll just let in enough light to the room to see it clearly. In this case, the room is correctly exposed.

If you don't open the door wide enough or long enough, the room is too dark meaning that it's underexposed. If you leave the door open too long you let in too much light and overexpose the room.

I am pretty certain that you may have already seen over-exposed and under-exposed photos before, but it may not be clear which was which so here a quick run through of each of the different types of exposures.

Under Exposure

Under-exposed photos look like they are behind a thin veil of black silk: colors are muted, shadows are very dark, and the entire photo looks drab. 

Overexposure

If I were to describe an overexposed photo, it would be that they look like a scene from a sci-fi movie when the alien ships are landing. Everything is washed out in bright light, and all texture and color is lost.         

Correct Exposure

A correctly exposed photo looks pretty much as it did when you were looking at the scene with your eyes before you took it.

 

Colors are natural, shadows aren't pure black, and there is plenty of detail in the entire photo.      

In AUTO, Program, Aperture Priority and Shutter Priority modes, your camera is always trying to capture photos like the last one in this set, where the exposure is balanced.

But there will come a time when you're going to have to tweak the exposure settings. You can adjust exposure settings either to create a dramatic effect, or to compensate for challenging light that can trick your camera into making a bad exposure.

So how do you get used to adjusting the exposure settings on your own? The first step is learning how to read your digital SLR's light meter which will be talked about next time as well.

For now, knowing these definitions is going to make the rest of this topic easier to go through. Once again, if you have any questions, please ask. Until next time, happy shooting!