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Digital SLR Photography for Dummies Tutorial

Welcome to my digital SLR (dSLR) photography for dummies guide. With dSLR cameras getting cheaper and better by the day many friends are getting into photography, so I figure it would be helpful to write a simple guide for potential buyers and new owners. The goal is to provide a very basic introduction to get the ball rolling without being too technical. I will keep jargon to a minimum.

If you like this guide you can tell your friends about it, or check out my photos.

I'm dumb, what exactly is a digital SLR camera?

Digital SLR cameras are the big cameras you see photojournalists, paparazzi and other professionals photographers use. The three defining characteristic of a SLR camera

   manual control - you are in charge (if you want to be)
   interchangeable lens - pick the right lens for the situation
   optical viewfinder - look through the viewfinder to compose the photo

Manual control

We'll get to this later, but with SLR cameras you have total control of how the photograph will be taken.

The lens

When people say they have a Nikon D200 or Canon EOS Rebel SLR they are referring to the camera body. In addition to the camera body you will need to buy a lens.

a Nikon 50mm lens

The lens controls how the light enters the body to form the photograph. Typically, entry-level SLR cameras are sold with a "kit" lens, a standard lens you use to take normal photos. For example, Nikon sells a 18-55 mm (focal length in millimeter) kit lens with the D50 body.

The beauty of SLR cameras is you can buy additional lens depending on your needs. If you like to photograph birds and wildlife you will probably need a telephoto lens that lets you see things from far distances. Telephoto lens will have a longer focal length, for example, 300 mm. Telephoto lens are the lens you see sports photographer use from the sidelines of football games.

Maybe you like to take group photos at weddings. You will want a wide angle lens, say a 28 mm lens, to get a wide view of everybody.

These days most consumer (and even professional) lens are zoom lens. For example, I have an 18-200 mm lens, which is very versatile, since I can go from wide (18mm) to telephoto (200mm) without changing lens.

The viewfinder

The other defining trait of an SLR camera is the optical viewfinder. The viewfinder is the little opening in the camera you look through to see what the camera sees.

key components of SLR - click for larger version

Point-n-shoot cameras, those small cameras you can fit in your pocket, typically don't have viewfinders, and you see what the camera sees via an LCD screen. The problem with this is there is significant lag. If you move the camera around the LCD will not refresh fast enough, so it's not good for following moving subjects. Also, the image on the LCD tends to be too bright, not viewable in bright light and lacks detail. There are point-n-shoots with viewfinders, but those viewfinders are completely different than an SLR's viewfinder.

SLR look-alike cameras, so called full-featured cameras like the Canon PowerShot S3 IS or the Sony Cyber-shot DSC-H5, also have LCD screens for seeing what the camera sees, but also have electronic viewfinders (EVF). An EVF is just like a regular (optical) viewfinder, except it's really a mini LCD screen. While it doesn't have all the disadvantages of the large LCD it's still not ideal.

SLR cameras have optical viewfinders - what you see is what you get. The advantage is you can clearly see what you are about to photograph. At first it may seem less convenient than an LCD screen or an EVF, but once you get used to an optical viewfinder you will not want to go back. Incidentally, SLR stands for single-lens-reflex and the entire lens/viewfinder mechanism is what sets SLRs apart.

But wait, doesn't digital SLR cameras also have LCDs? Yes, they do, but only for viewing the photographs after they are taken.

How a photograph is made

Before getting into how to use your SLR we need a basic understanding of how a photograph is formed. Light enters the lens and falls on the camera's sensor to create a photo. It's as simple as that. Incidentally, when people talk about 6 mega pixels they are talking about the sensor and how much information the sensor can capture.

A certain amount of light falls on the sensor, and this creates the final photograph. If you let a lot of light reach the sensor your photograph will be too bright (overexposed). If you don't let enough light in your photograph will be too dark (underexposed). You want to let just enough light in to create a nice photograph. There is no correct amount of light. Whatever amount of light produces a photograph you like is the correct amount.

Controlling light

So how do you control the amount of light falling on the sensor? Through aperture and shutter speed.

click for larger version

Think of aperture as a window in a house. If you have a big window a lot of light will enter. A small window won't let as much light in.

But there's more; there is the shutter speed. Think of the shutter speed as how long you keep the window's blinds open. Initially the blinds are closed. You then open the blinds for some amount of time before closing them again. The longer you keep the blinds open, the more light will enter through the window. Keeping the windows open for 1 second will let in less light than if the windows were kept opened for 5 seconds.

Let's recap. To control how much light falls on the sensor you choose what size window (aperture) and how long you want to keep the blinds open for (shutter speed).

Sensitivity

But wait, there is one more thing. How sensitive is the sensor? Some people are very sensitive to the sun so don't need much sun light to get burnt, while others are not very sensitive and need more sun light to get burnt. The camera's sensor works similarly.

With SLR cameras you can control how sensitive the sensor is (this is not technically true but ignore that for now). You can set the camera to be very sensitive, so you don't need as much light to create your photograph. Or, you can decrease the sensitivity, meaning you need more light.

There is a trade-off to consider. The more sensitive you set your camera to, the more noise you will get in your photos. You will need less light, but your photos will contain random dots, possible making it very grainy.

You typically don't want to set your camera to high sensitivity unless you need to. For example, it is a dark room and you don't have enough light, so you make your camera more sensitive to the light you have.

In photography this sensitivity is called ISO. You probably seen it before on film designations - ISO 400, ISO 200, etc. The higher the ISO number, the more sensitive your camera's sensor is set to. So you will typically set your ISO to the lowest available, say 100 or 200. Then you bump up the ISO depending on the lighting needs.

How to use your SLR

We've learned a photograph is made by letting a certain amount of light fall on the sensor, and we've learned (conceptually) how to control this amount of light. Now let's apply it.

Manual mode

In full manual mode you control both the size of the window (aperture) and how long the blind stays open (shutter speed).

1. Set the ISO sensitivity to the lowest number possible, say 100 or 200.
2. Select an aperture opening (how big of a window)
3. Select a shutter speed (how long to keep the blinds open)
4. Hit the shutter release button
5. Enjoy your photo

The question is, how do you know how much light is needed? SLR cameras have fancy computer chips that helps you meter the light. After you select an aperture and a shutter speed the camera will tell you if there's too much light or not enough light. You can use this information to help you select different aperture/shutter speed combinations, until the desired amount of light is obtained.

The meter readout (typically seen in the viewfinder) will look something like this.

This means you are very overexposed and letting in too much light (the plus sign). So either make the window smaller or open the blinds for a shorter duration, or both.

If you see something like this

it means you are a little underexposed and don't have enough light (the minus sign). Either make the window larger or open the blinds for longer, or both.

You want the meter readout to be in the middle, indicating optimal exposure.

Also remember that in addition to adjusting the window size and blind opening duration you can also change your ISO sensitivity. If you are underexposed you can increase the ISO from 200 to say 400, knowing that you may get some extra noise. If you are overexposed you can decrease the ISO, say from 200 to 100. Since there are limits to the ISO range, typically 100 to 1600, you have to taken this limitation into account.

How does the camera meter

For the curious, you might be asking, how does the camera meter? How does it know a photograph will be underexposed or overexposed? The answer is the camera doesn't, it's just a best guess. For a given aperture/shutter speed/ISO combination the camera will calculate how the light/colors are distributed. If the distribution is skewed, say there's too much dark tones, the camera will indicate underexposure. Camera's are pretty good at this, but many times, especially in tricky lighting situations, the guess will be wrong and you have to use your judgment.

Too much control

Most of the time you probably don't want to shoot in full manual mode because you have to control both aperture and shutter speed (and ISO). To make it easier SLR cameras have aperture priority mode where you only have to control the aperture (window size) and shutter priority mode where you only have to control the shutter speed (duration blinds stay open).

Typically you don't need to constantly change the ISO sensitivity, so we'll assumed ISO is fixed, but remember, for any mode, you can change the sensitivity to control how much light is required.

Aperture priority mode

"A" mode is like manual mode, except you only control the aperture. You pick an aperture, the camera will adjust the shutter speed to give you what it thinks will be a properly exposed photograph.

Recall aperture is the size of the window. Large windows have small aperture numbers. A large window will have a small aperture number of f/1.4. Small windows have large aperture numbers. A small window will have a large aperture number of f/22. There are window sizes in between, with corresponding aperture numbers that change accordingly.

large window --> small f-number (for example f/1.4)
small window --> large f-number (for example f/22)

You use the dial on the camera to select an aperture, and the camera will select the shutter speed for you. For example, say you are outside in the bright sun. You select f/3.5. The camera might select a shutter speed of 1/500 of a second (blinds only need to stay open for a little bit). Now you go inside to a dimly lit room. With the same f/3.5 aperture selected the camera might choose a shutter speed of 1/2 second (blinds need to be opened longer).

So which aperture should you select? Why f/3.5 and not f/1.4?

First, the lens will have a range you can select from. A very expensive, "fast" lens might let you select apertures from f/1.4 (large window) to f/22 (small window). A cheaper, more "amateur" lens will be "slower", with a range starting at say f/3.5. Fast refers to the fact that a large windows (small f-number) requires the blinds to be kept opened only for a short duration (fast), and slow is the opposite.

So, given your lens constraints, why f/3.5 and not f/11? There are two reasons. One is motion blur and stabilization. The other is artistic - how you want your photos to look.

Remember, all things being equal, if you have a small f-number (large window), you require faster shutter speeds (blinds open briefly). Faster shutter speeds freezes the action and prevents your shaky hands from making the photo blurry. If you are taking action shoots you typically need to select an f-number so the shutter speed will be fast and you can freeze the action.

Even if you are taking a completely still photograph, say of a building, if you select an aperture that results in a slow shutter speed you risk your shaky hands creating blurry photos.

So, the first rule is you need to select an aperture that will result in a shutter speed that won't create blurry photos due to shaky hands or the subject moving.

The other factor in selecting an aperture is how you want the photograph to look.

Say you want to take some photographs of a landscape, full of trees, mountains and flowers. The mountain is far away, but the tree is a little closer. You want both the tree and mountain to be in focus and sharp. You select a small window (large f-number, say f/11). Typically, larger f-numbers (smaller windows) will make things sharper and more things in focus.

building in back and balloons in front both in focus

But let's say you want to take a photo of your friend's face (a portrait), and don't really want the background to distract. You want the face to be in focus, but the background to be out of focus, creating an intentional blurry/faded look. You select a larger window opening (smaller f-number, say f/1.8).

background out of focus

larger f-number --> smaller window opening --> background/foreground in focus, sharper
smaller f-number --> larger window opening --> subject in focus, background/foreground out of focus, not as sharp

Shutter priority mode

Shutter priority mode is exactly like aperture priority, except you select a shutter speed and the camera will choose an aperture it thinks will produce a good photo.

Why would you want to use shutter priority? I touched on this early regarding having a shutter speed that is fast enough to prevent blurry photos from shaky hands, or if you want to freeze the action.

The "old" rule of thumb is the minimum shutter speed you need is the reciprocal of the lens' focal length. So, if you are zooming in at 70mm to take a photo, the shutter speed should be 1/70th of a second or faster (such as 1/160th of second). In practice, it's better to do something like two or three times the focal length. For example, at 70mm you would do 1/(3*70) = 1/210th of a second or faster. This depends on how steady your hands are.

The other point is freezing the action. Say you are photographing your dog who likes to run around a lot. If you select too slow a shutter speed the dog will appear blurry, producing ghosting. You need a faster shutter speed to freeze the movement. The faster your dog is moving, the faster the shutter speed you need.

Summary table

Here's a little cheat sheet. It's not exact, just to give you general idea. In particular, depending on the specific lens, sharpness may not continue to increase as the aperture decreases. Typically, a lens will not be super sharp at lower f-numbers (f/1.4). Then the sharpness will increase as the f-number increases to a certain point. Then sharpness may fall off again. So f/11 may be sharper than f/22.

shutter speed / aperture	f/1.4 (large window)	=========================> image sharper foreground more in focus background more in focus	f/22 (small window)
1/500th second (blinds open briefly)	amount of light reaching sensor "base" aperture effect subject in focus background not in focus foreground not in focus not as sharp shutter speed effect freezes action no blurry from shaky hands		amount of light reaching sensor much less than "base" aperture effect subject in focus background in focus foreground in focus sharp shutter speed effect freezes action no blurry from shaky hands
\|\| \|\| blurry due to shaky hands \|\| movement will not be frozen \|\| \|\| \/
1 seconds (blinds open longer)	amount of light reaching sensor much more than "base" aperture effect subject in focus background not in focus foreground not in focus not as sharp shutter speed effect does not freezes action blurry from shaky hands		amount of light reaching sensor "base" aperture effect subject in focus background in focus foreground in focus sharp shutter speed effect does not freezes action blurry from shaky hands

In closing

That's about it. Hope you found this guide useful. Happy shooting.

January 28, 2007 - initial version