Deciding to make the jump into manual mode can be mildly terrifying. At first it will probably feel hopelessly complicated. There is some truth to that. It takes a lot of moving parts to make a truly brilliant image; many of those puzzle pieces are directly linked to your choice of settings`. Despite the steep learning curve, there’s no reason to fear that little M on the mode dial. This cheat sheet will help you figure out what does what and why.
Exposure and Metering:
In laymen’s terms, a properly exposed photograph is one that is neither too dark nor too light. To correctly expose an image you have to make sure that the right amount of light hits the sensor. Too much and the photo will be too bright, too little and your photo will be too dark.
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The light meter in your camera measures the light reflecting off your subject and calculates how your picture will be exposed based on your current settings. In automatic mode, you camera will take that information and change the settings for you. In manual mode you are responsible for manually setting the shutter speed, aperture, and ISO yourself.
To use your meter, look through the viewfinder. Along the bottom of your field of vision there will be a horizontal line with a series of vertical tick marks. Smack dab in the middle there will be a zero. That zero is what your camera thinks is perfect exposure. Some cameras are pretty spot on, others will require that the photographer under or over expose slightly. When you press your shutter half way your current exposure will pop up on that metered line somewhere. If it is to the left of the zero, your photo is underexposed and you need to let more light in somehow. If it is to the right, your image is overexposed and you need to shut some light out.
ISO measures how sensitive your camera’s internal sensor is to light. The sensor inside a DSLR camera is essentially the digital equivalent to film inside of a film SLR. High ISOs such as ISO 800 and up are very sensitive to light and are great for situations where light isn’t abundant. The downside is as you push the ISO up you are more likely to experience noise, unwanted grain, in your images. Low ISOs like IS0 100 through ISO 400 make your sensor less sensitive to light. They are great for situations where light is bright, such as outside on a sunny day.
Shutter speed is a measurement of how fast your shutter is opening and closing. The shutter itself is a mechanism in your camera that opens and closes to let light in. The light then hits the internal sensor and creates your image. If your shutter is open too long your photo will be overexposed and if it isn't open long enough your photo will be underexposed. Shutter speed is typically measured in the seconds or fractions of seconds the shutter is open. A shutter set to 1/100th of a second will be open 10 times longer than one set to 1/1000th of a second. It also controls how motion is captured in your imagery. Slow shutters speeds show motion while fast shutter speeds freeze motion. Say you are photographing a spinning top that is shaped like a star. At 1/60th of a second that top will simply be a blur but at 1/500th of a second you will likely be able to freeze the top in place, showing its true shape.
An aperture is a mechanism inside your lens that opens and closes. It sounds pretty simple but the aperture setting serves two main purposes and both of them are important. The first is that it’s a major player when it comes to controlling your depth of focus. Depth of focus is the amount of your image is in focus. A small depth of focus means that most of your photo is out of focus and a large depth of focus means most of your photo is in focus. The other element apertures effect is just how much light makes it to the sensor.
Wide apertures let in more light and decrease the depth of focus but are denoted by small numbers such as f/2.8. Narrow apertures let in less light by increase the depth of focus and are denoted by large numbers such as f/16.
Put It All Together
Changing one setting will require you to adjust the others. Is your photo too blurry? Up the shutter speed but remember you will probably have to widen the aperture or up your ISO. If you photo is overexposed you might need to increase your shutter speed or select a more narrow aperture or drop your ISO. You might even have to adjust all three. It gets easier with practice.