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Camera Basics

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Let’s talk cameras! In this article I hope to explain the basics of digital camera use, and what’s important to look for in a camera when making a purchase.

One of the reasons that I really enjoy photography is that as with engineering, everything is a trade-off. Take a car, for example. You want more horsepower so you add a bigger engine, but then you also add more weight, which will affect handling. So you use a smaller more high-strung engine, but then you lose low-end torque, and so on. With photography it’s more of everything in semi-focus vs one thing in sharp focus, or a grainy picture vs using a flash. So, onto the basics.

There are many settings on cameras, but the main two are shutter speed and aperture. When you push the shutter button to take a picture, the camera (or you) chooses a shutter speed (how long the lens exposes the film or digital sensor to light), and how wide the lens opens (aperture). Many other parameters need to be chosen by you or the camera’s automatic mode, but those two are the main parameters. Now we can get into the nitty-gritty of photography!

Shutter Speed/Time

As mentioned above, shutter time (or shutter speed) is how long the lens exposes the digital sensor, or film to light. It is measured in seconds or fractions of a second. For example, shutter speed might be 1/120, or one, one hundred twentieth of a second. Indoor pictures, or other low light conditions require a longer shutter opening time, than outdoor daylight conditions. When taking a picture on a bright sunny day of a shiny car, you might see a shutter time of 1/800. For indoor pictures, under standard lighting, you might see a shutter time of 1/30. For hand-held pictures, a slow shutter speed can result in blurry images. In general, anything less than 1/60 seconds can result in a blurry image. This varies from person to person, camera to camera, and how much zoom you are currently using. One can use a tripod, or a flash to compensate for this, but we’ll talk more on that later.

Aperture

Aperture is how wide the lens is open. Think of your eye, if you squint, you let in less light, whereas if you open your eye all the way, you let in much more light. One reason why aperture causes a lot of confusion is the way it is measured on the camera; the ‘F’ number. A large aperture value, or ‘F’ number is a small lens opening (not much light gets in), whereas a small aperture value is a large lens opening (lots of light gets in).

Figure 1: Large F Number - Small Aperture (small lens opening).

Figure 2: Small F Number - Large Aperture (large lens opening).

What’s important is the effect changes in aperture (lens opening) have on your pictures and in particular depth of field. For me, a better way to remember aperture values is a small aperture value (F number) results in a small depth of field, and a large aperture value results in a large/broad depth of field. So what’s depth of field?

Depth of Field

Depth of field is the distance in front of and behind the object focused upon that appears to be in focus. When you take a picture and the camera auto focuses on an object, only that object is precisely in focus. All of the other objects in the picture that are closer to the camera and further from the camera will be slightly out of focus. How much they are out of focus depends on -you guessed it- depth of field. A small or shallow depth of field will result in a picture where the object focused on is in very sharp focus. The things around said object will be blurry. How blurry depends on how far away they are from the object focused upon. A large or broad depth of field will result in the object being in somewhat good focus, and the objects around it being in somewhat good focus. Here in lies a photography trade-off. If you want everything to be in focus, the best you can do is snap a picture where everything is very slightly blurry. Or you can get a single object in perfect, sharp focus, but everything else is blurry.

Compare Figure 3, and Figure 4. In Figure 3 we use a large lens opening (small ‘F’ number) for a very shallow depth of field. The ball is in excellent focus, whereas objects in front of the ball (the fountain base), and objects behind the ball (wood pile) are blurry. In Figure 4, we used a small lens opening (large ‘F’ number), for a very large depth of field. Notice how the ball is not as sharp as in Figure 3, but that the base of the fountain is in much better focus.

Figure 3: Shallow Depth Of Field - Small ‘F’ Number - Large Lens Opening

Figure 4: Large Depth Of Field – Large F Number - Small Lens Opening

Keep in mind that a large lens opening (small ‘F” number) will let more light into the camera. This will allow you to use a faster shutter speed. The trade-off is that only the object focused upon will be in exact focus. If you use a small lens opening (large ‘F’ number), you will be required to use a longer shutter speed. This increases the chances of a blurry image, so a tripod may be necessary. In general portraits use a small depth of field (small ‘F’ number, large lens opening), so that the subject is in perfect focus and is the highlight of the photograph. All the other elements in the picture are blurred out. Landscape pictures usually use a large depth of field (large ‘F’ number, small lens opening) so that the entire picture is in focus; or at least, pretty good focus.

One last thing on depth of field is a real world use. If you look at a road sign far away with your eyes wide open, and it is blurry, try an experiment. Take you index finger and make a tiny hole to look through. If you look through this hole, it will be easier to read the far away road sign. This is because by looking through this pinhole, you are increasing you’re depth of field. This is also why we squint to see far away objects; by using our eyelids we are increasing our depth of field, and reducing the amount of incoming light into our eye.

Just to summarize – for a large depth of field use a large ‘F’ number, and hence a small lens opening or small aperture. For a shallow depth of field, use a small ‘F’ number, and hence a large lens opening or large aperture.

ISO

What is ISO? For digital cameras ISO is simply how sensitive the sensor (film) is to light. It is the same for film cameras. A higher ISO film (or setting on a digital camera) is a faster film – i.e. it is more sensitive to light. By using a higher ISO value, you can use a faster shutter speed to help reduce camera shake/blur. So why not always use the maximum ISO value? Another photography trade-off! The more sensitive you make the sensor to light (high ISO value) the grainier your picture will become. The less sensitive the sensor is to light (low ISO value) the more clear and sharp your picture will be. In general, you want to use the lowest ISO value that you can without reducing the shutter speed to the point where camera shake will result in a blurry image. Notice how the picture in Figure 5 is grainer than the picture in Figure 6. In particular look at the green wall. It is much smoother in Figure 5.

Figure 5: ISO 400

Figure 6: ISO 50


White Balance

Our eyes (or brain) can deceive us. When we’re outside what we perceive as white is different than what we think is white when under artificial light. Say you go to the paint store to pick out a color. You find one and it looks great in the store, but when you get home and try it out, it looks so much different! This is because of the lighting changes from the store to your home, and how our brain interprets what we see. The camera needs to know, for the current picture being taken, what ‘white’ is supposed to look like, or rather what we humans interpret white to be under certain lighting conditions.

On most modern digital cameras, white balance can be set to ‘Daylight’, ‘Cloudy’, ‘Tungsten’, or ‘Fluorescent’. If you choose ‘Daylight’ and take a picture under indoor lighting, everything in the photo will have a yellow tinge to it. See Figure 5, and 6 for an example. Notice how with the correct white balance (Figure 5) the light appears white.

Figure 7: Tungsten White Balance - Indoor Lighting.

Figure 8: Daylight White Balance - Indoor Lighting.


The Camera

Most consumer cameras have some sort of mode dial that might look like this:

 

When shopping for a camera, try to choose one that has the manual modes. These are Tv, Av, and M. Some manufacturers refer to these as S, A, and M. The Tv or S modes are shutter priority. In this mode, you choose the shutter speed, and the camera will choose the aperture for you to properly (if possible) expose the image. The Av or A mode is aperture priority. In this mode, you choose the aperture of the lens (‘F’ number), and the camera chooses the shutter speed to properly expose the photo. In the M mode, you choose both shutter speed and aperture; it’s up to you to expose the image correctly. In mode P, the camera chooses both aperture and shutter speed – but you are allowed to change ISO, White Balance and other parameters. The other modes are fully automatic, where the camera chooses everything for you. We won’t be using those modes; they’re boring!

If the camera has a longer than 5x zoom lens, I would recommend shopping for one that has image stabilization (IS) built in. This is a very valuable feature that allows you to take more hand-held pictures that turn out sharp, or at least sharper than without it. Some nice features to have are a high-speed mode, where the camera takes pictures continuously at a rate of around 2 or more frames per second, a swivel LCD, so that you can take pictures overhead and close to the ground, and the use of standard sized batteries such as double A’s. It’s important to try out a camera before purchase to see if it feels comfortable in your hand, to check how fast it focuses, if it zooms smoothly, and if the controls are easily accessed. If you’re purchasing a non-SLR camera, a movie mode is a very fun, and functional feature.

Picture Taking

Now that we have the basics down, let’s take some pictures! For most pictures, this is the thought process I go through. First, I make sure the white balance is set for the conditions of the photograph, and set the ISO as low as the camera will allow. Then, I set the camera for aperture priority; this is mode Av on most cameras. I consider what I want the photograph to look like, in particular depth of field; do I want everything in focus, or am I only concerned with a single subject being in sharp focus. Once that is decided I set the aperture of the camera, or the ‘F’ number. I then push the shutter button half way down so that the camera auto focuses, and gives me the shutter speed that it will use to take the picture. If I’m at the wide end of the zoom lens on the camera, and the shutter speed is less than 1/60, I need to make changes. Or, if I’m at the far end of the zoom (zoomed all the way in), and the shutter speed is less than 1/120, I’ll want to make changes because of the possibility of a blurry image due to camera shake. Those are simply guidelines; you’ll have to see what works best for you. If the camera reports back to me a shutter speed that is too slow, and therefore blurry images may result, I’ll need a way to shorten the shutter open time (increase the shutter speed). To accomplish that, I can do four things. I can either increase the ISO (which will increase the graininess of the picture), use a flash if appropriate, use a tripod, or open the lens up further by lowering the ‘F’ number and hence decreasing my depth of field. Once I make these adjustments, I again push the shutter button half way, and see what the resulting shutter speed will be. If it’s OK, then I recompose the shot, and snap the picture. These are general guidelines; we’ll look at some real world examples, after examining diffraction.

Diffraction

Say you throw a pebble into a lake, and you watch the waves spread out from that pebble. Now imagine there is rock in the way of one of those waves. What happens when the wave hits that rock is the water will curve around it. Light can be thought of as a wave, and has the same properties. There are two reasons to discuss diffraction here. One is that you can use it to create interesting photos, and the other is how it can directly affect your camera; in particular the lens. Examine the photograph in Figure 9. Notice how in the area around the rider, there is a glow, or blurry area. This is because the light from the sun is bending around the rider, in much same way the water wave bends around the rock.

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Figure 9: Diffraction.

This is how you can use diffraction to make interesting photographs. The aperture of the camera can also be affected by diffraction. As you close down the aperture on the lens and look through a smaller hole (increasing the ‘F’ number), the light can bend around the physical part of the aperture and cause distortion in your images. This is one of the reasons why closing down the aperture and increasing your depth of field causes items in the frame to become more blurry. The light is being diffracted around the physical aperture of the camera, as in Figure 4. The ball was being focused upon, but it is much less sharp than in Figure 3 with a wide lens opening (small ‘F’ number).

Portraits, Refraction, and Diffraction

If you’re taking a picture of your spouse, you want them to be the highlight of the picture. They are the most important. Right? You might be thinking, great, I know what to do, set the camera into Av mode, and choose the smallest ‘F” number to open the lens all the way up. Sounds great, except there is one problem; the problem of refraction. As light travels through different media such as air, water, and a camera lens, it changes speed. This change in speed causes the light to bend, or rather it causes us to interpret a bend. I could talk much longer on refraction, but the important point is that the most accurate parts of the lens are in the center, as it refracts light the least. The edges of the lens are the most optically inaccurate, because they refract (bend) light the most. So where does that lead us? Why, another photography trade-off! If you open the lens all the way to get the shallowest depth of field, you have exposed the most inaccurate part of the lens. As you decrease the aperture (close the lens down), and broaden your depth of field, you expose less of the inaccurate part of the lens, but then diffraction starts to come into play. In general, a good trade-off is to use one or two stops down from all the way open.

Landscape Photos

In general, for landscape photos, you’ll want to use a large ‘F’ number for a broad depth of field. You want the whole scene to be in focus. As we already discussed in the above section, diffraction can take its toll if we close down the lens opening too far. We also have the problem of slow shutter speeds because very little light can get through the tiny lens opening, which can result in blurry images. Thankfully, for landscape photographs, the rocks, trees, and mountains are not moving, and so a tripod can be used easily. For pictures like these, I find it’s best to vary the ‘F’ number from as large as it will go, to several stops lower. Then pick the picture that looks the best. If you don’t have a tripod, your only option is to increase the ISO until you have a shutter speed that will result in clear photos. Take a lot of shots, and take your time, the scene isn’t going anywhere!

Night Shots and Long Exposure Times

Night shots, such as Christmas lights, monuments, fireworks, and cities can be really fun, but you will certainly need a tripod or something to hold the camera still while the shutter is open and exposing the digital sensor to light. This may sound odd, but as always, start with the smallest ISO the camera supports. For these pictures, we’ll be using the cameras full manual mode; usually marked ‘M’. If your camera does not have a remote shutter button, you can do a little trick. Use the camera’s timer, and, if possible, set it for a short time such as two seconds. By doing this, you can have your hands off of the camera when the shutter opens.

In general, by leaving the shutter open longer, you will get more of a star effect on lighting in your photo. This can be accomplished by adjusting the ‘F’ number to higher values so that less light goes through the lens. Then you will need to crank up the shutter time so that your photo is properly exposed.

Figure 10: Night Shot - F 3.5 - Exposure 2 Seconds.

Figure 11: Night Shot - F 8.0 - Exposure 15 Seconds.

Notice the star effect on the lights of the Christmas tree in Figure 11 with the long exposure time of 15 seconds. When using these long exposure times, it’s very important that your subject is completely still – otherwise the subject will be blurry. On nearly all consumer digital cameras (non-SLR), you can adjust the shutter speed and aperture while viewing a live preview. This is very helpful in finding good shutter speeds for night photographs. In general, you will still need to view the resulting image and make small adjustments, but you can get very close by using the live preview.

Lightning Shots

How to photographers get those crazy lighting shots? Were they just lucky and happen to hit the shutter button at the right time? If not, how did they do that? The answer is a long exposure time, a broad depth of field (large ‘F’ number), and many pictures taken. Here is how I go about it. Mount the camera on a tripod, and set it in the full manual ‘M’ mode. Naturally, you’ll have to wait for a good storm, and find a safe location (and perhaps a dry one) where you can view the sky. Set the ISO to the lowest setting, crank up that ‘F’ number, and set the shutter speed. The shutter speed will depend on how dark the sky is – if it’s a nighttime storm, you can use a very long exposure time (15+seconds). If it’s during the day, you’ll have to use shorter exposure times (5 seconds). In either case, it’s a good idea to take a couple test pictures at the long exposure time to make sure you’re not getting all white clouds, or other overexposed objects in the picture. Try to use the longest exposure time possible given the conditions of the sky and storm. Next up, start taking pictures! As long as the lightning occurs while the shutter is open, you will capture it. The lighting is very bright, and therefore will be captured by the digital sensor; it then disappears and so will not be overexposed despite the shutter still being open. Some cameras have a mode where you can set a number of pictures to take. For example, you can specify that after the timer goes off, take 10 pictures. This is very helpful when taking lighting pictures. You simply have to take enough photos, and have enough patience for the lighting to occur while the shutter is open.

Figure 12: Lighting Shot - F 8.0 - 13 Second Exposure Time.

Photography is a very fun and rewarding hobby that is now more accessible than ever before thanks to digital cameras. You can experiment as much as you want without worrying about cost of film or development. I hope you have enjoyed this article and found it informative and helpful. Now get out there and take some pictures - loads of pictures.

Last Updated on Saturday, 01 January 2011 05:54