Shutter speed, aperture, and ISO

Exposure is the most basic element of photography

If you want to be a photographer, you absolutely must learn how to control the exposure of a picture.  It will take a minute, but this page has everything you need to know.  Click on the different camera settings on the interactive exposure tool above to practice your exposure!

In the next few paragraphs, I'll explain exposure in the simplest and easiest terms I know how.  But you should also know that I teach a 30-Day Online Photography Class JUST for beginning photographers, where I teach exposure and other basic topics in much better detail. Check out the beginning photography class here.

Exposure is the total amount of light which is captured on a camera sensor during the process of taking a photograph. Digital cameras have three techniques to control the amount of light which is captured by the camera: shutter speed, aperture, and ISO.

Shutter speed

There is a “blinder” in your camera which covers the camera sensor.  The blinder quickly allows a slit of light through the lens to touch the imaging sensor in the camera, which captures the light. The longer the shutter is open, the brighter the image.

Have you ever wondered why your pictures are often blurry in low-light situations or when the subject of the image is moving quickly? Slow shutter speeds allow lots of light to touch the sensor, but if anything in the image has moved while the sensor is open, the photograph will reflect that movement. We can’t hold a camera perfectly still because our hands shake–that’s why we use tripods. The answer to every blurry picture is to make the shutter speed quicker, but for some situations, such as a moving object in the dark, quick shutter speeds can have the negative effect of a darker image, since the camera has less time to capture the light. Shutter speed is the total amount of time the blinder allows for light to pass through to the sensor, and it is measured in fractions of a second. A shutter speed for shooting a party in a dim restaurant might be 1/60th of a second, while an image at the beach on a bright day might be as fast as 1/4000th of a second.


The aperture is a circular (sort of) hole through which the light passes to the sensor. A smaller hole allows less light and consequently produces a darker image. Perhaps even more important than the amount of light is the depth of field. It basically controls the amount of the picture that is in focus and the amount of the picture that has a nice creamy blur. Aperture is generally expressed in f-stops on a camera. If you want a portrait of a baby with a nice creamy background, a low f-stop, such as 3.5 is used, whereas if you want to take a landscape image with everything in focus, then you’ll want an f-stop like 11 or 22. The low f-stop of 3.5 allows lots of light, whereas a high f-stop like 11 or 22 would not allow much light to get to the sensor and produces a darker image. In essence, low aperture allows lots of light and short depth of field; a high aperture allows little light and makes the entire image in focus.


ISO can best be described as magic. It makes the camera sensor more sensitive to light. The low-light sensitivity is one area in which technology is moving forward rapidly as professional photographers have pushed manufacturers toward this objective. A low ISO such as 100 will produce a darker image than an ISO of 800. However, ISO comes at a high price. If a photographer uses a high ISO such as 800 or above, digital noise becomes visible on the image. (Click here to read about the dangers of expandable ISO.) Digital noise is a grainy look on an image and is never desirable. Different cameras deal with digital noise better than others, but most entry-level cameras should not be raised above ISO 400 unless the aperture and shutter speed cannot offer an acceptable alternative. In short, ISO is a last-resort bit of magic for more light.

Shooting Modes

The aperture, shutter, and ISO buttons on a DSLR camera
Select the shooting mode by using this dial on the top of your DSLR

Your camera has many shooting modes. On all DSLRs, you can choose a shooting mode by twisting the dial on top of the camera. You’ll see several icons to describe different situations in which the camera can adjust to choose the settings for you. For example, if you choose an icon for a portrait, the camera will choose a low aperture value so you can get a creamy background. These semi-automatic modes are okay for those who aren’t interested in photography, but if you want professional results, you will need to move into the creative shooting modes 100% of the time.
DSLRs have four creative shooting modes: Program mode (P), Shutter Priority (Tv or S), Aperture Priority (Av or A), and Manual Mode (M).

Program mode (P)  is never used by professional photographers. It is similar to the fully-automatic “idiot mode,” but allows a couple creative choices.

Shutter Priority (S or TV)  has some use if depth of field is not as important to an image as getting a moving object to be sharp without any motion blur. Choosing this mode means that you will choose the shutter speed and the ISO and the camera will choose a matching aperture value to properly expose the image. Some people might choose this for sports photography, where the important thing is the shutter speed and the aperture is not as important.

Aperture Priority (A or AV) is the mode that professional photographers use 90% of the time. Aperture priority mode allows the photographer to choose the aperture and the ISO, but lets the camera find the corresponding shutter speed to achieve a correct exposure. The reason that this is the best mode for all-around photography is that the photographer can pay attention to depth-of-field without being distracted by shutter speed when it isn't as important.

Manual Mode (M)  is very useful in some specialized situations where the other exposure modes cannot accurately capture the photographer’s vision. As a landscape and HDR photographer, I'm in manual mode most of the time, but I would rarely use it to shoot portraits or sports.

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33 thoughts on “Shutter speed, aperture, and ISO”

  1. Your explanations are some of the easiest I have read, but I am about to lose my mind!!! I have a Nikon D3100 and get AWESOME portraits (school pics, senior pics). I am having a HORRIBLE issue with family/group shots though!! I have played and played and PLAYED with the darn settings on this camera and I just CANNOT get EVERYONE in a group to be IN FOCUS. I have read tons of other postings on other sites about other people having the same issue with this specific camera. Have you experienced this issue or is my brain just totally fried and I’m still doing something completely wrong?! (Which I would’t doubt – I have three kids – four if you include my husband . . ) ANY help you give at all on this would be GREATLY appreciated (and may prevent me from being carried away by the men in white coats! 🙂 Thanks!

    1. Hi Lori, what lens are you using? on a cropped censor camera like yours I would suggest a 24 or 28mm lens, using a minimum f7.1 apeture, image size set to large/fine and composing the shot for deliberate cropping. Hope this of some help.

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  3. The F-Stops and shutter speeds ALWAYS confused me, until now!!! THANK YOU SO MUCH FOR EXPLAINING THIS TO ME IN LAYMAN’S TERMS!!!!!!!! You don’t know how excited I am to start using the A/AV mode on my DSLR. lol! I usually shoot with 35mm film and use a light meter…and JUST purchased a Nikon D3200 2 days ago! Thank you thank you thank you!

  4. I am a complete newbie and have bought my DSLR for photographing primarily hedgehogs. Everyone (to the point of being sick of hearing it) tells me photos are better not using flash but the hedgehogs are always blurred if I don’t so I keep going back to using flash but I want to learn. Is it possible to photograph a fast moving object in low light or shall I just keep using flash and ignore them?

    1. @elle_vee:disqus it is very possible to get better shots in low light. You have seen that you need to have your shutter speed high in order to keep those rascals sharp, so that means you have to change the other two parts of the exposure triangle – ISO and/or Aperture. Taking the ISO up high adds noise, but sometimes that can be very manageable. Taking the Aperture down in number to something like 2.8, 1.8, or 1.4 can really add a lot of light, but the lenses capable of doing that are more expensive and your depth of field (the area in the shot that is in focus) becomes much narrower. It is a balancing act to figure out how you set all three variables that make up the exposure of a shot that you have to manage based on what you are trying to do.

      In this case, I don’t think flash is the best choice if you want the animal to stick around. I am guessing they take off pretty fast when the flash goes off, so I would think you would want to try to get the shot without a flash in this case. If you have some room to open up the Aperture (lower the number) then I would try that. If you can’t do that, try taking the ISO up and see what you think of the shot. Ultimately you may discover that the lighting conditions are beyond the gear you currently have and you would have to either add more light (flash) or have to get gear that is more capable of working in this specific situation like a faster lens.

      Hopefully that helps. Good luck!

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  6. Thanks for this, a party on Saturday night and a new DSLR – and have never used one before. I am going for AV, and will try F6-8 range (based on 22 includes background and 3.5 blurs background), and lower to create some blurring. ISO will be in the 100/200 area depending on the available lighting. I have a flash, and I feel some what more confident just to have a go, especially as the AV will work out what the shutter speed needs to be. I have learnt all this from your insights, so again, thanks.

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