So you’ve graduated from your iPhone’s camera, great! Now what? I’m assuming you’ve bought yourself a digital SLR camera (DSLR) or at the very least a compact system camera that has interchangeable lenses. I think of the compact system as a “hybrid” camera as it has some features of a SLR, but also retains many of the automated functions that make point-and-shoots so popular. Now you’d like to know more about using a DSLR camera! You’ve come to the right site!
Before we begin talking about the camera and its functions, I need to explain what I consider the three tenets of photography: light, time, and sensitivity. The interplay of these three features creates a photograph via a proper exposure amount. Whether it was a hundred years ago with black and white film, or modern day digital photography, the principles of a photography are the same – as light hits a sensor (in the “old days,” film), a reaction takes place to capture the image. However, if light continues to hit the sensor, eventually the sensor no longer has any “sensitivity” remaining to provide any relevant image. The image has become overexposed (all white). Therefore an ideal image is the correct balance of amount of light transmitted to the sensor and the sensitivity of the sensor itself.
What determines the amount of light that hits the sensor? Two things: the aperture and the shutter speed. The aperture is the opening of the lens through which light passes. Now here’s the tricky part, the smaller the number, the larger the opening. The term f-stop (or f/stop) is used to denote the aperture size. Decreasing the f-stop increases the aperture opening. The larger the opening the more light. The f-stop is entirely dependent on your lens and has nothing to do with the camera itself. F-stops will range from as low as 1.4 to usually 22. F-stops have a funny way of counting that I don’t need to explain here. Full f-stop values are as follows: 2, 2.8, 4, 5.6, 8, 11, 16. With each subsequent number allowing twice as much light through the lens for any given amount of time. You can Wikipedia a list of partial f-stops if you want as your dSLR camera will allow you to toggle within the range of apertures for the given lens.
Shutter speed, simply the amount of time the lens’ aperture remains open, also determines how much light will hit the camera sensor. The longer the shutter is open (the slower the speed), the more light will get in. Shutter speeds range from 1/4000th of a second on the extremely fast end, to seconds or even minutes on the long end. Some SLRs even have a function where the shutter speed stays open as long as you want it to. This is the bulb function and the shutter will stay open as long as the shutter button is held down.
Now what about sensitivity? On SLRs, you can actually control how sensitive you want the camera sensor to be to light. This is called the ISO. The lower the ISO number, the less sensitive the sensor is to light. Why would you want a less sensitive sensor? Because with increased sensitivity, you introduce “noise” to a picture. Noisy images appear grainy, particularly in dark regions of the picture, and lose sharpness and edge detail. However increased sensitivity means that the sensor needs less total light to produce an image. This can come in handy if you have limited light, or are limited by one of the other two tenets – shutter speed or aperture.
When using your digital SLR, always consider Aperture x Shutter Speed x ISO = Image Exposure. Ok, it’s not really a multiplication formula, but the point is that if you do something to diminish the amount of light hitting the sensor by changing the aperture, you have to either change the ISO or shutter speed to maintain the same exposure. Doubling your aperture size increases the amount of light entering the camera for a given unit of time, therefore you either have to cut your shutter speed in half or lower the ISO to make the sensor “half as sensitive.”
Take a look below (and remember that f-stops count in a funny fashion and 2.8 is actually twice 4)
|F/Stop||Shutter Speed (sec)||ISO|
What do you notice about these 4 different combinations? In comparison between the first two rows, we’ve cut the aperture size in half. Therefore, the shutter speed needed to be doubled (1/2000 to 1/1000) to maintain the same exposure. If we kept the same shutter speed (third row), we need to make the ISO twice as sensitive. So, all 4 of the combinations above produce the same exposure. If you want to learn more about exposure, and the interplay of aperture, shutter speed and ISO, I found Understanding Exposure by Bryan Peterson a very helpful book.
Now you’re ready to dive into your SLR! Unlike that old point-and-shoot that has already begun collecting dust in a closet somewhere, SLR cameras give you full control of aperture, shutter speed, and ISO (in addition to overall exposure, but that is another article). You’ll want control over these functions to increase your creative expression of a scene you photograph (also another article).
Take a look at the main dial of your SLR. If you have a Canon camera, you’ll see labels Av, Tv, and M. They are exposure modes and stand for “Aperture Value” “Time Value” and “Manual.” For Nikon, the labels are A (for aperture), S (for shutter) and M (manual). If you don’t have a Canon or a Nikon, well then, you chose poorly! Just kidding, but you should be able to figure out the company’s labeling system. Anyway, with Av, you the skilled photographer set the aperture, and the camera, based on an ISO you have also set, will give you the “proper” shutter speed. With Tv, you determine the shutter speed and the camera will give you the appropriate aperture, limited by the maximum and minimum size based on the lens you are using.
M or full manual mode is more tricky – you are responsible for setting both the aperture and shutter speed. In the viewfinder of the camera you will see a bunch of vertically oriented hashmarks. As you change aperture or shutterspeed, a blinking hashmark will move towards the left or the right. When it is aligned in the center, the camera is telling you it believes you have a proper exposure.Tags: Aperture, Camera Operation, ISO, Shutter Speed