Learning your DSLR: What is Aperture?

Last week we talked about ISO and today I want to talk about Aperture also referred to as f-stop.

Aperture is measured in f-stops which is adjusted in order to change the amount of light that reaches the light sensor when you take a photo. The size of the opening will allow more or less light in when the shutter goes off. Your camera will have f-stops that look like f/4.0, f/4.5, f/5.0, f/5.6, f/6.3, f/7.1, etc. The numbers are fractions so when you compare 4.0 which is a bigger number to 7.1 the camera will allow more light to enter at 4.0. Photographers like to play with the f-stop because it also helps determine depth of field.

Changing your Aperture (f-stop)

First, get your user manual and adjust your camera to the setting that allows you to change your Aperture only. This is referred to Aperture Priority. You will want to be sure your camera is on Auto ISO in this setting.

Now you need to assess your surroundings for lighting and what depth of field you need.

A shallow depth of field measured in f-stop such as 2.8 means you have more background blur and with a large depth of field measured in f-stop such as 7.1, more of your image will be in focus. This is important to consider when you are photographing a scene as opposed to one person or object.

See the difference in depth of field just with the flowers being 6 inches away from the floor with image 1 [ISO 160, Aperture f/2.8, Shutter 1/60sec], image2 [ISO 500, Aperture f/5.0, Shutter 1/60sec], and image 3 [ISO 2500, Aperture f/11, Shutter 1/80sec]. Notice how the ISO and Shutter adjusted automatically in order for the camera to correctly expose the image.

Once you understand what your depth of field needs to be, ask yourself, how will that impact the amount of light that will hit the sensor? Set your camera to 7.1 and take your test photo. The camera auto settings for shutter and ISO adjusted based on the standard exposure it is trying to find. Now take the same image with your camera set to 4.0. Compare the shutter and ISO settings to your first image.


ISO and Aperture working together

Let’s put together what we learned so far with ISO and Aperture using your test images. The ISO number would be larger to account for less light with your 7.1 f-stop for your first image compared to your image using 4.0 as your f-stop.

To further explain this relationship, keeping your camera in the Aperture priority setting, change your ISO to a variety of different settings and continue to take the same image while adjusting the settings. For example, in Aperture priority set your camera to 5.0 f-stop and ISO 100 for your test image. Now take the same image with the same f-stop but with ISO 1000. You will see not only how your shutter setting adapted for this but also how important getting all three settings correct is in order to capture the image in the way you intend.

Next week, we talk about shutter speed, which determines how long the shutter will stay open to let in enough light to properly expose your image. Are you seeing a common theme? Lighting is very important to getting your image captured correctly.

Enjoy working with your new DSLR and please go to our Facebook page and share your pictures!