DSLR Basics: Shutter Speed, Aperture, and ISO

So you’ve decided you wanted to get into photography? My guess is that you either already have a DSLR, borrowed one from a friend, or you are seriously considering getting one. Once you have one in your hands, you’re probably wondering, how do you use this thing to take good photos? What does P/A/S/M mean? How do I take a photo where the background is blurry? And what are all of these buttons for?

Sometimes there are a lot of questions, and other times there are just blank stares when someone asks me to show them how to use their camera. I think the basics of how a camera works is a good starting point. This way you can begin to understand how some of the photos you have seen are taken, and how you can start taking photos like those too.

To photograph is ‘to write with light’. ‘Photo-‘ meaning light, and ‘-graph’ meaning to write. Your camera is a tool in which you capture the light in a controlled way, and you control the light by using shutter speed, aperture, and ISO.

Shutter Speed

Shutter Speed is how long your camera stays open for when you press the shutter button.   When looking at your settings, it is usually the number that is a fraction on your camera because you are typically shooting in fractions of a second. On some cameras, they may just show whole numbers (as seen below on my FujiFilm), but all of the numbers should be interpreted as fractions.

A general rule of thumb is to keep your shutter speed faster than 1/60th of a second if you are not using a tripod. This is because most people are not going to be able to hold the camera completely still for longer than 1/60th of a second, and there will like be motion blur. There is some wiggle room here. I can usually get away with holding the camera at 1/30th of a second, but not every photo is guaranteed to be sharp.

A short shutter speed is a fast shutter speed and will result in photos that ‘freeze’ your subject in motion as seen in the image below. Usually, a shutter speed of 1/100 of a second will freeze a person walking, but you would probably want to use a faster speed for animals, waves, or people who are running or jumping.

Waves shot with a shutter speed of 1/3200th of a second

A long shutter speed will show motion blur and is commonly used to show light in motion or an object over time. Some common examples of long exposure shots include star trails, cars at night, and waterfalls.

Light painting/motion blur shot at 1/80th of a second


Aperture is how wide your lens is open while taking a photo. The wider your lens is open the smaller your depth of field will be. This results in a blurry background. If you have a very small aperture, then your photo will have a large depth of field, which results in a sharp picture overall.

Aperture is a little bit confusing because the numbering is a bit counter intuitive to the wording. The wider the aperture is, the smaller the number is. The smaller the aperture is, the larger the number is. The aperture is usually indicated with by a number with an ‘f’ in front of it. The image below, on the left, is using a wide aperture. It is set at f2.8 so everything outside of the small depth of field is blurry. In the image on the right, a smaller aperture was used, f8.0. Although the camera is in focus on the camels head, almost the whole image appears to be sharp and in focus.

Aperture is different than focusing and the focal point. That said, the closer you are to your focal point, the more of an effect the depth of field will appear to have. (Think macro photography, like of flowers and such). Just try to remember, when it comes to aperture, small number = blurry background, and large number = sharp background.


ISO is probably the thing you will use the least out of these three controls. Although it is useful to know as you grow more familiar with taking photos, and especially when you are trying to stick to a specific aperture or shutter speed for artistic effect. ISO stands for International Standards Organization if you were wondering. All you need to know is that ISO controls the camera’s sensitivity to light. The smaller the number, the less sensitive to light the camera is, and the larger the number, the more sensitive the camera is to light.

So a good rule of thumb, that I learned in photo class, is to use 100 ISO for bright, sunny days, and to use 400 ISO for gloomy, overcast days. That was back when I was using film though. Most DSLR’s advertise as having huge ISO capabilities now such as 20,000 or more. Even with this huge range, you won’t usually need to go over 1600 ISO, unless you are shooting at night or in a very low light setting. And there is a catch to these higher ISO speeds.

The higher the ISO you use, the more ‘noise’ you will get. Noise, in the film photography world, is known as grain. Sometimes this is a desired look, especially with film photography. However, with digital, it can get ugly. Especially when you are shooting in low light conditions. Here are some photos that show how digital noise compares to film grain.

(likely) ISO 400 film, shot of Holga film camera, zoomed in so grain can be seen better


ISO 1600, shot on Sony a99, zoomed in so noise can be seen better

Another thing to note is that some DSLR’s handle noise better than others. The biggest factor for how a camera handles noise is the sensor size.  I won’t get into this too much right now, but the bigger the sensor you have in your camera, the better the camera is at handling and reducing noise. Generally, your entry level DSLR isn’t going to be the best at handling noise. You can also reduce some digital noise by using a photo editing software like Lightroom or Photoshop, but this tends to make the photo a bit ‘soft’ or fuzzy (as you can see above). So if you can, I would recommend using an ISO below 1600 just to play it safe.

Now that I’ve gone basics of shutter speed, ISO, and aperture. I can touch on what P/A/S/M is. These are standard shooting modes on DSLR cameras. Each one allows you more or less control over the shutter speed, ISO, and aperture. These modes are found on the mode dial of your DSLR. Below is an image of what this looks like on my Sony. The Fujifilm X100T does not have this dial because it only shoots in manual mode. Late disclaimer: it technically isn’t a DSLR.

Mode dial on Sony a99

Programmed Auto (P)

In Programmed Auto mode, your camera will automatically select your shutter speed, ISO and aperture for you based off of the lighting conditions. Basically, you won’t have any artistic control over the photo taken, but you should get a well-exposed photo while using this mode.

I generally encourage people to not use program mode. Instead, I would recommend practicing in one of the other modes. However, program mode could be a good way of getting to know what settings are good for what lighting conditions, since your camera will still show what aperture and shutter speed are being used.

Aperture Priority Mode (A)

Aperture priority mode will allow you to select the aperture, and then the camera will select a shutter speed for you so you take a properly exposed photo. You can typically also adjust the ISO in this mode if you would like. Aperture priority is great for when you want to shoot at a specific aperture, but don’t want to manually adjust the shutter speed every time the lighting changes. For example, I might use this when taking portraits, since I like the background to be soft when taking portraits. When taking portraits, you usually want to be able to focus on posing and directing the person, and not necessarily your camera settings.

You do need to be mindful of your shutter speed when using aperture priority mode though. As I said before, if you shutter speed becomes too slow, you will get motion blur either from your subject moving or from camera shake. It is easy to forget that you are using a slow shutter speed. Sometimes, the motion blur is so little that you don’t even see it until you review the photos on your computer. I know, I’ve done it myself, and it is a bummer. So remember to check your shutter speed!

Shutter Priority Mode (S)

Shutter priority mode is exactly like aperture priority mode, except that you select the shutter speed and then the camera chooses the best aperture for the lighting conditions. I personally don’t use this mode often, as I prefer specific apertures to specific shutter speeds.

This mode is really useful if you are taking action photos. For example, sports, wildlife, and other things that move fast… I would say in shutter priority mode, more so than aperture priority mode, you do not want to be fussing with your camera settings when you are trying to capture a specific moment. If you are trying to take a picture of a bird, you aren’t going to have time to manually expose your photo before the bird is gone, and then you have to wait another 20 minutes for the bird to come back. In addition, you don’t want to risk motion blur of such a fast moving object, so in this case, you want your main focus to be control over the shutter speed.

Manual Mode (M)

Manual mode is the free-for-all mode. Full control but a lot of room for mistakes. I almost exclusively shoot in manual mode. I guess that is because I did three years of film photography before going digital, and I’m used to having to adjust everything on the fly.

When using manual mode, you have to manually adjust the aperture, shutter speed, and ISO for a properly exposed photo. Every camera will have a light meter of some sort to let you know that the photo is properly exposed. You can also use the histogram.The photos below show the light meter on my Sony a99. The first image shows that the photo is going to be underexposed by putting the arrow on the left side of the middle line. The middle, bold line, is where your ideal exposure is. You can also tell that the photo is going to be under exposed because there is a negative number to the right of the graph.

The photos below show the light meter on my Sony a99. The first image shows that the photo is going to be underexposed by putting the arrow on the left side of the middle line. The middle, bold line, is where your ideal exposure is. You can also tell that the photo is going to be under exposed because there is a negative number to the right of the graph. -1.7 means that the photo would be -1.7 EV steps underexposed. (An EV step is just a measurement of the exposure).

camera menu showing current settings are going to underexpose photo

The second image shows the camera menu when the image is properly exposed. The arrow is right in the center, and the number to the right indicates that the photo is not over or under exposed by any EV stops.

camera menu showing current settings are going to properly expose photo

This last photo shows that my photo will be overexposed. The arrow is now to the right of the middle line, and the number on the right shows that this image would be 1 EV step overexposed.

camera menu showing current settings are going to overexpose photo

That was a lot of technical info.

The main benefit to shooting in manual mode is that you don’t have to shoot a properly exposed photo. Stylistically, that isn’t always what you are going for.

Both overexposed and underexposed photos are really trendy now. I’ve usually seen overexposed photos for portraits, babies, that kind of thing. Really bright photos are inviting, soft, and (usually) give you a feeling of warmth. So it makes sense that you would want your wedding, baby, and family photos to evoke this sort of feeling. I’ve seen underexposed photos more in editorial work, lifestyle photos, and a ton of Instagram accounts. #moodygrams

This is the part that makes photography fun, for me. Experimenting with your camera to create different effects, different styles. Even take it a step further and try different cameras and different lenses to see how they take photos differently. So really, just start taking photos, play with the settings, and you’ll figure it out, even if you don’t understand all of the technical jargon.