Digital Photography 101: Aperture

This is part three of a series of articles I’m writing about digital photography, as I learn more about it. You can find links to the other articles at the bottom of this one.

No, we’re not talking about Aperture, the software application from Apple. We’re talking about the Aperture on your SLR camera in this article.

After I answered some questions for myself about Film Speed, I started wondering: “What’s this f-stop Aperture thing that people keep telling me about?”

So, I sat down last night, and read a bunch of websites, and then took a bunch of photos (all inside) with different lenses to see if I could figure out what Aperture was.

The best way I can explain it is this:

Aperture is the diaphram that sits inside the lens on your camera. The aperture setting is the size of the opening between the outside world and your film or digital sensor that controls how much light passes through the lens to your sensor. It controls light and impacts depth of field.

Aperture is also related to shutter speed, which can also be used to control the amount of light that reaches your sensor, but impacts the amount of blur in your photos, not depth of field.

Together, aperture and shutter speed affect exposure, and the goal is to get the right exposure at the aperture and shutter speed you want to get.

Aperture + Shutter Speed = Exposure.

This is a key point to understand when thinking about photography. All cameras have a shutter, and all lenses have an aperture. They are manipulated to get the proper exposure for your shot, depending on what kind of settings you use.

Let’s talk about those settings.

Lenses can have a fixed aperture, or a variable aperture. I haven’t made any judgements or assumptions about which type is better: fixed or variable, though I’ve heard for professional photos, having a lens that allows you to fix the aperture while shooting is preferrable, so you can control more aspects of the process.

Apertures are usually denoted in f-numbers. f/22, f/16, f/11, f/8.0, f/5.6, f/4.0, f/2.8, f/2.0, etc…

It’s confusing for a beginner, but, if you can remember this, you’re set:

The bigger the f-number, the smaller the aperture.
The smaller the f-number, the bigger the aperture.


image borrowed from Wikipedia

So, a f/2.0 aperture is actually bigger in physical size than an f/2.8 or f/4.0 aperture.

Say it with me: The smaller the number, the bigger the aperture.

So, combined with the shutter speed, the aperture setting of your lens creates the amount of light exposed on the film or sense in your camera. But…

Aperture also adds that important photographic element called “Depth of Field” which is basically how you get a fuzzy background or a sharp background in your photo… you focus the image on an object, then to get the right depth of field, you set the aperture bigger (smaller number) to get fuzzier backgrounds. If you’d like to have sharper images, you need a smaller aperture (bigger number) so that your lens focuses across a larger space. Depth of Field is also very much affected by the focal length of your lens.

I’ll follow this article up with one on shutter speed, exposure and depth of field, and lenses, so stay tune. I’ll also link all of these articles together with added images to complete the whole process as I write them.

Other sites worth reading if you want to learn more about Aperture are:

Other articles in this series:

And you can browse the rest of the Photography + Video category on this site for more links to relevant content.

10 Responses to “Digital Photography 101: Aperture”


  • Great post.

    With most point and shoots, the set aperture is the same situation as the 400 ISO film speed. Most people will want portraits and a large depth of field, so the average camera will be set for that. Unless you get really close the lens, most things will be in focus.

    Anything prosumer and up should have customizable settings, and rightfully so. Composing an image involves all the aspects of the three fourths rule (not always thought, but in a general sense, yes), lighting, shutter speed, and aperture. It’s also like a swing, where each aspect affects the other, and as a photographer you have to compensate for those aspects while shooting.

    The style of a photograph can easily be affected by the shutter and the aperture, but with the aperture you have to adjust the shutter accordingly. So having a large depth of field may not be an option if you subject will be blurred by a slow shutter and camera shake. Most often, the golden rule for the shutter speed is another formula involving the focal length, but I don’t want to spoil possible future installments of the 101 course, so I will refrain. :P

    Anyway, the ideas are relatively simple to understand, but once applied to shooting in situations that require quick decisions, these concepts become more essential than it appears to be. I can remember so many times I wanted a shot a certain way, but because of lighting situations, I ended up with slight blur or not the right depth of field.

  • Hi,
    Well written introduction to aperture (not the Apple Software or for that matter one of the best photography magazines ever published. In my opinion, variable aperture lenses are always the way to go Amatuer or professional. In understanding the relationship between aperture and shutter speed, it is always wise to remember the law of reciprocity that governs nost things photographic from film speed vs. grain in film selection to time vs. temperature in developing to aperture vs. shutter speed in exposure. Also, it is helpful in remembering the counter intuitive
    “smaller f-stop = more light” thing by realizing that the f-stop numbers are actually the bottom half of fractions. the top half having been eliminated from camera ring notation because of space. Therefore, f:2 is actually f:1/2
    and f:4 is actually f:1/4 etc. Pete

  • thank you for explaining everything in laymens terms. i’m just starting back with my nikon fm2 camera and i have forgotten every thing. i guess what i’m trying to find out is what is the rule of thumb about: if you have your aperture on f5.6 , what should you have your shutter speed on,etc. or does it matter? i understand the light and openings but something is not clicking for me. kathy

  • Excellent!

    I feel more confident to play around with manual settings on my camera now

  • Excellent article
    Thank you

  • Very good blog page about aperture. Excellent. Congrats.

  • thaank you for exxplaining everything in laymens terms. i’m just starting back with my nikon fm2 camera and i have forgotten every thing. i guess what i’m trying to find out is what is the rule of thumb about: if youu have your aperture on f5.6 , what should you have your shutter speed on,etc. or does it matter? i understand the light and openings but something is not clicking for me. kathy

  • Very good blog page about aperture. Excellent. Congrats.

  • You just post excellent information about aperture. Keep up good work!

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