The Exposure Meter; How to Achieve the Correct Exposure in Manual Mode
I always had a knack for taking good pictures; I always seemed to be able to find and frame the perfect shot. So when my father bought my husband and I a Nikon D5100 for our wedding gift, I was overjoyed. Little did I know of the aggravation. Sure, I had a basic understanding of aperture, shutter speed, and ISO. But when I took my camera to Hawaii for our honeymoon, the pictures did turn out nice (how could you go wrong in Hawaii) but not great. They were either underexposed or overexposed and I ended up taking three shots of every scene. Once I truly learned how to use the exposure meter did picture taking become easier. If only had I known this a few months ago.
Aperture, Shutter Speed, and ISO
Aperture is the size of the lens opening. It determines how much light you allow to pass to the sensor. It also determines depth of field. On a camera aperture is denoted by f-stops, such as f5.6 or f11. The larger the aperture, the smaller the f-stop and vice versa. If you are interested in photographing one subject such as a person or a pot of flowers but not landscapes, then a large aperture or small f-stop will do. If your interested in landscape photography or making sure both the background and foreground are in focus, you want a small aperture or large f-stop. In another hub, I will explain how sometimes a large aperture and small aperture setting make very little difference. But for now, follow these guidelines.
Shutter speed refers to how long the shutter is left open. It is measured in seconds. A shutter speed of 1/4 would mean the shutter is left open for 1/4 of a second. If you are taking pictures of objects in motion, such as your child on a bike, you of course want a quick shutter speed or the picture will blur (unless you are trying to be creative and include blur). If the object is still, shutter speed doesn't matter except that the longer the shutter is open the more light gets to the sensor, which you could use to your advantage indoors or on a cloudy day.
ISO determines how sensitive the camera sensor is to light. You usually want an ISO below 400 to prevent noise. The only times you want a higher ISO is with nighttime shots, where you need all the light reaching the sensor that you can get, or if the exposure meter says you are underexposed with the aperture and shutter speed settings you have selected. Remember, doubling your ISO reduces the required shutter speed time in half. I like the analogy in the book Understanding Exposure, 3rd Edition, How to Shoot Great Photographs with Any Camera. Think of ISO as bees. The more bees you have making honey, the shorter the time it will take to get the job done.
The Exposure Meter
The exposure meter looks like a backwards number line in mathematics on your camera's display with + on the left, - on the right and 0 in the middle. If there is an arrow towards the + side, you are overexposed. If the arrow is pointing towards the -, as seen in the image to the right, you are underexposed. If there is no arrow at all, your exposure is perfect there is no need to make any changes. To determine what the exposure is for your shot, point your camera at your subject, press the shutter release button down halfway, and read the exposure meter. If the meter reads overexposed, too much light is getting to the sensor, reduce your aperture or ISO or increase you shutter speed. If the meter reads underexposed, then too little light is getting to the sensor, increase your aperture, ISO or decrease your shutter speed.
Step 1: Setting the Aperture
First things first, set your aperture. Examine the subject of your photo. If you want a large depth of field, choose a large f-stop, f16 or greater. If you want a shallow depth of field, choose a small f-stop, f5.6 or below. Let's say, for example, you are sitting in front of your house and you want to take a picture of the old house down the street. But you also want to include in the picture the street with the shadows of the trees . Because the volume (thinking mathematically) or depth of field is large, you want a small aperture or large f-stop. Now let's say you are taking a picture of your flower in your garden. Because you are only interested in the flower garden, a small aperture will do.
Step 2: Choosing Your Shutter Speed
Now with your aperture set, hold the shutter button down halfway to focus on your subject. Take a look at the exposure meter either through the eyepiece or on the view screen. If the exposure meter reads that you are overexposed (+) or underexposed (-) you want to adjust your shutter speed until you are at 0, or a little underexposed which is OK too.
Step 3: Dealing with ISO
I always set my ISO at 200 to begin with. If your exposure is not correct and you cannot adjust your shutter speed any further, you may need to adjust your ISO. Here are two examples. Suppose it is dark outside, and for the largest aperture and the slowest shutter speed, you are still underexposed. You need to increase the ISO and then adjust the shutter speed. Or, let's say, the shutter speed set is just too slow for the picture you want to take. Again increase the ISO and change the shutter speed so the exposure meter reads that you have perfect exposure. Remember, a large ISO setting may result in noise so you may need to go back to step 1 and adjust your aperture.
Dealing with Built-in Flash
I rarely use flash except when I'm taking a picture of people and there is shadow, due to the Sun, or if my husband, for example, is sitting in his old chair next to the window, under the lamp. Night or day he will always turn out too dark, either due to the sunlight coming in from the window or the artificial light of the lamp. If you must use flash, change your shutter speed so the exposure meter reads a little underexposed. If the exposure meter is at 0 the picture will be a bit overexposed due to the excess light not in the picture when the sensor makes it's initial judgement.