Accurate exposure start with you correctly setting the lens aperture and shutter speed (and ISO too, I guess.) You can set the exposure yourself manually or let the camera do it for you. The manual method requires either a separate hand-held light meter or you can use the one that’s built into the camera. For 90% of photographs you’ll make, the metering systems inside DSLR and mirrorless cameras do a fantastic job in producing correct exposure but its those last 10% that’ll kill you, so sometimes you have to shift into manual mode.
Manual mode is for shooters who would rather drive a car with a stick shift than an automatic transmission. That’s because there are lighting situations that can confuse even the most sophisticated automatic exposure system. Manual exposure can be especially helpful are required with high subject contrast and strong backlight but also when a specific mood is desired. (Consult your manual for the specific controls that adjust aperture and shutter speed.)
Some purists claim that manual exposure mode is the only one to use but outdoors I’ll use all the letters on the dial. In the studio I’ll use manual exposure mode with electronic flash7, LED and fluorescent light sources, such as this portrait of Pamela Simpson made with a Panasonic GH4 and Olympus 45mm f/1.8 and an exposure of 1/80 sec at f/1.8 and ISO 800. Sometimes, I will use a fairly slow shutter speed to pick up some of the ambient room light and a smallish aperture to maintain sharpness throughout the portrait.
Tip: Many cameras also offer a Bulb mode where the shutter stays open as long as the shutter release is pressed. This allows you to make really long exposures for subjects such as holiday lights or fireworks or special effects such as images of carnivals and amusement parks. Time exposures like this should be made using a sturdy tripod and you can further reduce the risk of camera shake by tripping the shutter using a cable release.
If you’re interested in shooting portraits and how I use cameras, lenses and lighting in my in-home studio, please pick up a copy of “Studio Lighting Anywhere” which is available from Amazon.com with used copies (as I write this) selling for less than $8—the best deal you’ll find anywhere. New copies are $17.50, take your choice.