Photography Basics: Understanding Exposure


Understanding exposure in boudoir

Exposure is the amount of light that reaches the sensor in your camera. Understanding exposure and how it affects your photos is one of the first step towards taking better images, no matter if you are a couple shooting together or you are doing self-shot boudoir.


Here are the subjects we will be going over in this post:

  • Exposure Triangle

  • Stops of Light

  • Under and Over Exposure

  • Light Metering

  • Electronic Viewfinder

Exposure Triangle

Aperture, shutter speed, and ISO are the three points of the exposure triangle and they work together to harness the light entering your camera and come together to create a photo. If you change one you will also need to change one of the others to compensate if you want to keep the same exposure.


Exposure triangle in photography

Graphic by WClarke and Samsara of Wikipedia Commons


Aperture is the opening through which light enters the camera and hits the sensor. A fast or wide aperture allows more light into the camera and produces a shallow depth of field. A slow or narrow aperture reduces the amount of light coming into the camera and produces a large depth of field. Depth of field is the area in front of you that is in focus. You can see aperture and depth of field on the right side of the triangle.


Aperture is represented using f-stop. With f-stop aperture is expressed as f/X, where X represents the aperture opening such as f/2. The lower the f-stop, such as f/1.8, the faster the aperture and more light enters your camera. The higher the f-stop, such as f/8, the slower the aperture and less light enters your camera. You can see this on the right side of the triangle.


Shutter speed controls how long your shutter remains open to gather light into the camera. The longer the shutter speed, the more light that enters the camera. A longer shutter speed can be used to create blur in an image. If you instead want a sharp image you will want to use a fast shutter speed, as you can see on the left side of the triangle.


A good rule of thumb is to keep the shutter speed at the reciprocal of the focal length or faster. For example if you have a 50mm lens on your camera, or a 35mm on a crop sensor camera, you would use a shutter speed of 1/50 sec or faster. If you have image stabilization in your body or lens you can go a little lower than that. But, you will still need to be aware of motion blur if the subject is moving.


ISO measures the sensitivity of the sensor. Think of it as artificial light. On a film camera the ISO is controlled by the film you are using. In this instance you would have to swap the film cartridge in order to change the ISO. Thankfully, with digital cameras that isn’t necessary as the camera handles this for you. ISO is represented on the bottom of the triangle.


One thing to be aware of when raising your ISO is noise. Noise makes your image look soft and grainy while reducing sharpness. Noise happens when raising your ISO to higher levels. Some cameras can go to really high ISO and still yield usable photos while others can’t. My old Nikon d3300 could only go up to ISO 800 before I started to see a lot of noise. On the other hand my Canon RP can easily go up to ISO 1600 before I start to see too much noise.


Stops of Light

A stop of light is a method of measuring the increase or decrease of light entering your camera. Each stop is double the amount of light if you are increasing the light coming into your camera or half the amount of light if you are decreasing the light coming into your camera. Your cameras light meter uses stops of light to help you get your exposure the way you want when you are taking photos.


The easiest way to explain it is with shutter speed. If you go from a 1 second shutter speed to a 2 second shutter speed you have double the light coming into the camera. This is one stop. If you go from a 2 second shutter speed down to a 1 second shutter speed you have halved the light entering the camera. This is also one stop.


The same is true for ISO. If you go from 100 ISO to 200 ISO you have increased the light entering your camera by 1 stop. Likewise if you go from ISO 200 to ISO 100 you have gone down 1 stop of light.


Aperture is different. With aperture if you double your aperture, say from f/2 to f/4. You aren’t going up by 1 stop of light, you are going up 2 stops of light. This is due to the diameter of the aperture blades not being linear.


Under and Over Exposure

Sometimes you will see or hear a photographer talking about under or over exposing an image. What they are talking about is when a photo is darker or brighter than what the camera is telling them is the correct exposure.


Sunrises and sunsets are an excellent example of when you would want to intentionally underexpose your image. Most cameras will try to expose for the whole scene which includes the foreground and will cause it to overexpose on the important parts, the beautiful colors and light in the sky. By under exposing you can bring out the colors and light in the sky to get the image you actually want.


If you over expose your image too much you can do what is called blowing out your highlights. Blowing out your highlights means that you lose detail in the brighter part of your image and you can no longer recover it in post processing. This is why some photographers intentionally stop down by 1 stop. I do this myself.


Light Metering

Your camera has a built in meter that determines how much light is in the frame and tries to balance the darker sections and lighter sections in your image. You can see it at the bottom of the screen when shooting in manual mode with most cameras.


While the light meter is a great tool, don’t always trust it to give you the best image possible. If you are going for a dark and moody image then you might need to under expose your image if you are looking at your light meter. When in manual mode this is easy as all you do is change aperture, shutter speed, or ISO. If you aren’t in manual mode you will want to use your cameras exposure compensation setting to get the camera to make the image either lighter or darker.


Electronic View Finder

Mirrorless cameras have an electronic view finder (EVF) where DSLRs have an optical view finder. The benefit of an EVF is that you can see in real time the exposure that you will get when you take a photo. This makes getting the exposure you want much easier, especially when using manual mode. This is one of the reasons I recommend mirrorless cameras over DSLRs. Since getting my Canon RP, which is a mirrorless camera, I no longer end up with images that are either way too dark or way too bright if the light changes or I forgot to change a setting.


In Closing

Understanding exposure will help take your photography from basic to something resembling art. Next up in the Photography Basics series will be shooting modes and why you don't want to be using Auto mode when shooting. For the next article in the Photography Basics Series click below.

Photography Basics: Shooting Modes

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