- Jul 12, 2008
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- Your "Whispering Eye"
Hey guys I stumbled across this on another forum. I found it really helpful so I thought I'd share. It an explanation of the basics of a DSLR and some scenarios for taking pics. Hope this can be a help to someone. This write up was done by DCR-5 on thespeedlounge.com
Part 1 is below and Part 2 can be seen on page 2
Part 1 is below and Part 2 can be seen on page 2
Hey guys... I put this together for my mom and some friends and I figured that I'd post it here to help out... This tutorial assumes you have a DSLR and starts you in Manual mode. I shoot Canon and wrote it for Canon users, but the buttons should be pretty universal. This is by no means they only way to shot or think about photography, but I think it represents a clear explanation of the three major factors that determine exposure. Please excuse the diagrams... I had few resources when I put it together and didn't even have those files on my computer. I'll upload the original diagrams on Monday from my work machine.
If you are reading this, chances are you just got a new camera, but I bet you didn’t realize that you already owned the most advanced and sophisticated camera and lens combination available, the human brain and eyes. As you look around the room or even at this written text, your eyes (the human version of the lens) are constantly adjusting the zoom, focus and aperture to read and see. The brain then takes that information, processes it and applies adjustments so that everything is understood and colors are correct (our own version photoshop). Have you ever looked at a sunset and marveled at how perfect the colors where and then tried to take a picture and the result didn’t look as good as what your eye saw? The reason for that is that your eyes and brain are constantly making adjustments so that every color looks perfect. When you look at the orange sky, your pupil dilates to let the perfect amount of light in to recognize the best orange. As your gaze moves to the ocean, it readjusts so that you get the best blue color. When taking a picture, you can only dial in one set of adjustments to capture the entire scene. You might dial in the perfect settings to capture the blue, but then everything else might be lighter than you like, or if you dial in settings to capture the orange perfectly, then the blue might end up being too dark, or almost even black. You have to find a best fit, compromise to get all of the colors to match as closely as possible. The wider the range from dark colors to light colors, the more compromise you have to make.
In its simplest terms, Photography is the capture of light on a light sensitive paper or sensor. In order to properly expose the scene that you are trying to photograph, there are three variables that can be adjusted: ISO, Aperture, and Shutter Speed. While making changes to each of these affects the amount of light captured, each one has its own characteristics, advantages and disadvantages that come along with those adjustments. In order to properly expose the scene, you must balance how much light each one is allowing to reach the film or sensor. I’ll outline each one along with its positives and negatives.
Shutter Speed is the measurement of the amount of time used to expose the picture. It is probably the easiest aspect to grasp, so we’ll cover it first. When you press the shutter button on your camera, the mirror that is directing the light through the lens and up to your eye in the viewfinder, flips up and a metal curtain lifts up (or sideways or rotates, the direction doesn’t really matter) and out of the way allowing what you’ve seen in the viewfinder to reach the film or sensor and create a picture. The curtain then comes down and the capture is finished. The amount of time that the curtain is up, allowing light to hit the film, is the shutter speed. It can range from 30 seconds to 1/8000th of a second (in some professional model cameras). The longer the shutter is open, the more light gets in, so in a dark situation, you’ll need a longer exposure. Let’s imagine that we want to take a picture of something moving fast, like a bird in flight, and it is a sunny day. We could use a very fast shutter speed, 1/1000th of a second for example, to freeze the bird in mid-air and perhaps even in the midst of it flapping its wings. Now, let’s imagine that we want to take a picture of a potted plant on the window sill, but its dark in the room. We can either turn a light on or we can use a slow shutter speed (think longer amount of time) to capture the picture. This might seem like a viable option, but you’ll quickly realize that as hard as you try to be steady, if you use a slow shutter speed, your hands will shake and it will produce a blurry image. This is a situation where you might need a tri-pod… or you can adjust your Aperture or ISO, allowing you to use a faster shutter speed? Using a tripod mounted camera with a slow shutter speed works for stationary objects, but if you are going to shoot people, even people sitting still, you’ll need to use a faster shutter speed.
**Note- As a general rule of thumb, the slowest shutter speed that I can hand hold is, “1/focal length of the lens”, so if I’m using a 50mm lens, I can hold the camera steady 1/50th of a second. If I’m using a 70-200mm zoom lens and I have the lens zoomed to 135mm, I can hand hold to 1/135th of a second. This is different for everyone. If you have really good technique and you can be steady like a sniper, you might be able to go much slower, so test it out for yourself**
Let’s go back to the example of our potted plant. We have all of the lights turned on and we just can’t make it any brighter. Additionally, we don’t have a tripod, so we can’t steady the camera and the picture is blurry because we have to use a slow shutter speed in order to get a good exposure. For the sake of our example, let’s say we are using a 85mm lens and our shutter speed is 1/50th. If we try to make it any faster to reduce the blurriness, it is too dark. This is a perfect case for ISO adjustment. ISO is a measurement of the film or sensor’s sensitivity to light. When referring to film, some people call it film speed or ASA. Most of the digital cameras reference it as ISO. The most common numbers associated with ISO are 100, 200, 400, 800 and 1600. These were the common sensitivities that film could be purchased in, and as digital cameras have come into existence, they’ve kept the same number and scale referring to the sensitivity adjustments of the sensor. You’ll notice that the numbers double with each step up. This is to show that ISO 400 is twice as sensitive to light as ISO 200 and ISO 100 is half the sensitivity of ISO 200. The higher the number, the more sensitive to light the film or sensor is going to be, so in a dark or dimly lit situation you want a higher number. There is less available light, so you want the sensor to be more sensitive to capture as much available light as you can. Recently, camera companies have begun adding intermediate 1/3 stop increments of the standard ISO settings, as well as allowing the capability to expand ISO settings with custom functions for extremely low-light situations. In these cases, the ISO values are as follows, 50, 100, 125, 160, 200, 250, 320, 400, 500, 640, 800, 1000, 1250, 1600, 2000, 2500, 3200, 6400. This allows for greater flexibility with your settings and allows you to only go up just as much as you need to limit any negative effects. Now that you understand ISO, let’s apply it to our example of the plant. We were using an 85mm lens and we see now that with our ISO setting of 400, we needed a shutter speed of 1/50th to get the exposure, but that was too slow to hand hold the camera without any shake or blurriness. If we adjust our ISO up to 800 (doubling the sensitivity), we can now use a shutter that is twice as fast, 1/100th, to get the same exposure and now we’ve eliminated the shake. You might think to yourself, wow this ISO thing is great, I’m just going to set it high and leave it there, however, there are drawbacks to using higher ISO settings. On film, the higher ISO produces a grainier picture. On digital cameras, higher ISO settings produce noise. This shows up as green, red and blue speckles and is caused by the individual pixels on the sensor beginning to heat up and incorrectly capturing the colors. The general rule of thumb is that you want to try and keep your ISO setting as low as possible in order to achieve the shot you want.
With shutter speed and ISO taken care of, the only thing left is aperture and it can be the trickiest to understand. In every lens there is a diaphragm that controls how much light comes through the lens and gets to the sensor. This diaphragm is called the Aperture and it functions much like the pupil of the eye. In a dark room, your pupil gets bigger to allow more light in, so you need to make the aperture bigger in your lens to let more light in. The lens aperture is usually specified as an f-number. Typical examples of Aperture values might be f/1.4, f/2, f/2.8, f/4, f/5.6, and f/8. Just like with ISO, each of these numbers I’ve listed represents a doubling or halving of the amount of area of opening and twice as much or half as much light. The tricky part here is that a lower number represents a larger opening and consequently more light getting into the camera. **Note… f/4 is not twice as much as f/8, it is actually 4 times as much, because you’ve gone up two stops.** Again, there are 1/3 stop increments in between each of the numbers I’ve listed (for example f/4, f/4.5, f/5, f/5.6, f/6.3, f/7.1, f/8) A lens that features an aperture of f/2.8 or larger (remember that means lower numbers) is often referred to as a fast lens because it will allow you to shoot in lower light conditions with faster shutter speeds,. Let’s go back to our potted plant. Now we’ve got an 85mm lens, our ISO is 800 and we’ve got a shutter speed of 1/100th to get that perfect exposure, but we see that there is a bee flying around the plant and we want to freeze him. We could adjust our ISO again, up to 1600 to get a shutter speed of 1/200th, but at ISO 1600 we are concerned that the extra noise might ruin the quality of our picture. We check our aperture and we see that its f/8. If we go down to f/5.6 (remember, smaller number means bigger opening and more light, I told you it’s tricky), we can leave our ISO at 800 and still get the shutter speed of 1/200th that we need to properly expose the plant and freeze the bee in flight. At this point, you may be thinking that Aperture is great and you’re just going to set it at the highest available aperture, but unfortunately, Aperture doesn’t just effect the amount of light coming into the camera. When you increase the aperture (smaller number) you also decrease the Depth of Focus or DOF. You may decrease the depth so much that your entire subject is no longer in focus. This can be a hard concept to explain so I’ve attached two small diagrams (ok, so I’m not great at drawing in Photoshop)
^^^Depth of focus at f/8
^^^Depth of focus at f/2.8
From the two diagrams, you can see that that as you’ve increased the Aperture, the depth of focus has gotten narrower. This isn’t necessarily a negative though. I am sure you’ve all seen photographs where the subject is in sharper focus, but the background has that beautiful blurry effect, that helps to really isolate and highlight the subject. That is called bokeh, and it comes from the perfect use of aperture. Selecting the perfect aperture, not only effects the exposure of your shot but also adds to the creative aspect of your shot. Using a larger aperture can also effect the sharpness of your shots. When a lens is designed, the light coming through the center is always going to be the sharpest, as the aperture gets larger, there is some fall off in the sharpness as light is coming through the outermost regions of glass. In order the keep the sharp at very large engineers, the designers have to follow strict quality control and used only the best materials, making the lenses significantly more expensive. Additionally, the extra light that is let in by the larger aperture also aids the autofocus of the camera, allowing it to autofocus faster. The aperture is a function of the lens because that is where the diaphragm is contained, but it is adjusted using the camera (you are basically telling the camera what setting to adjust the lens to). It is shown on a lens as 70-200mm f/4. This means that the maximum aperture that this lens is capable of is f/4 and you can select f/4 anywhere through its zoom range of 70mm to 200mm. They don’t bother to list the minimum because usually we are shooting in conditions where light is limited, not infinite. If we were shooting on the sun, then maybe the minimum would be the most important thing. You may come across inexpensive zoom lenses that feature a variable aperture designation, such as 75-300 f/4-5.6. This designation means that at 75mm we can dial in a maximum aperture of f/4, but at 300mm we can only dial in a maximum aperture of f/5.6. ** Note..If you are using one of these lenses in AV and you are at 75mm and f/4 and then zoom to 300mm, the camera will automatically adjust your aperture to f/5.6 and then select the corresponding shutter speed… this will make more sense as I explain AV mode in just a second.**
At this point, you’ve just learned to take a picture in Manual mode on your camera (M on the Canon dial). It probably felt creative, but wasn’t very fast. Now that we have an understanding of what each of the functions does, we can begin to use the Shutter Priority and Aperture Priority settings (TV and AV on the Canon dial) so that we can decide which factors is most important to us and allow the camera to make the other decisions to help speed up the process. I’ll take you through my thought process of shooting.
Let’s say for example that we are hiking on a trail and we see a beautiful flower. We want to take a picture where the flower is in sharp focus, but the surrounding plants become a blurry, green backdrop. For this shot, we want to use Aperture Priority (AV) because we want to select a large aperture (small number) to give us that narrow depth of field. Remember that you want it to be narrow enough that the whole flower is in focus and the background is blurry, but not so narrow that the whole flower isn’t in focus. First we are going to set the ISO. If it is a normal sunny day, I’d recommend starting at ISO 400. Then we are going to dial in an aperture. It might take you a few shots to dial in the perfect aperture for this effect (good thing we aren’t shooting film). Once you dial in the aperture, compose the shot and press the shutter button halfway. This will autofocus the lens and tell the camera to meter, or judge the scene for exposure (I almost always use autofocus. On modern cameras and lenses it is accurate almost 100% of the time and super fast. I only use manual when I’m going for some sort of special effect or the camera is having trouble recognizing what to focus on…I’ll go into more on this later). In AV mode, you select the aperture and ISO and the camera will make a decision on what the shutter speed should be to correctly expose the shot. Remember to keep an eye on the shutter speed, if it is too slow and you are hand-holding… you might get that dreaded camera shake. If the shutter speed is too slow, bump up the ISO one more stop (or if your camera has 1/3 stops of ISO) so that you now get a shutter speed that is sufficient. If the shutter speed is excessively fast, maybe 1/1000th, chances are you can probably bump the ISO down a notch to help reduce the chance of that digital noise. Do you see the compromise decisions we are making?
With AV done, let’s look at Shutter Priority (TV). Imagine we’ve just taken the flower shot and we are now further along on our nature hike. We see a bald eagle flying over a pond and want to get a shot of it. In this instance, it might be best to use shutter priority so that we can set a fast shutter speed to make sure that we capture the bird. We’ll adjust our dial to TV, set our ISO back to 400 for a starting point and then dial in a shutter speed of 1/500th. We’ll compose the shot, following the bird and making sure that we use our center Autofocus point (The center AF point is usually the fastest and most accurate…. I find that the automatic AF point select mode on most cameras doesn’t work very well). Press the shutter button halfway to lock on autofocus and the camera will again meter the scene, this time selecting the correct aperture to expose the shot. Remember to pay attention to the aperture that the camera selects. If it selects an aperture that is too narrow the whole eagle might not be in focus. If this happens, adjust your ISO higher in order to make the sensor more sensitive to light, so the camera can use a smaller aperture (larger number) that has a greater depth of focus. Inversely, if it is giving you an aperture that is small (larger number) you may want to bump the ISO down a notch to help reduce noise.
That’s it… that’s the crash course in photography exposure basics. Now, go out and shoot… try all of the different settings. You have the LCD on the back of the camera and you can use it to learn as you go along.