Photography 101.5 - Aperture

Photography 101.5 – Aperture

Photo 101.5 aperture

Photo: Rainer Ebert used under CC license

The following post is from Australian photographer Neil Creek who is part of the Fine Art Photoblog, and is developing his blog as a resource for the passionate photographer.

Welcome to the fifth lesson in Photography 101 – A Basic Course on the Camera. In this series, we cover all the basics of camera design and use. We talk about the ‘exposure triangle’: shutter speed, aperture and ISO. We talk about focus, depth of field and sharpness, as well as how lenses work, what focal lengths mean and how they put light on the sensor. We also look at the camera itself, how it works, what all the options mean and how they affect your photos.

This week’s lesson is Aperture.

Here’s What We’ve Covered Previously in this series:

Lesson 1: Light and the Pinhole Camera
Lesson 2: Lenses and Focus
Lesson 3: Lenses, Light and Magnification
Lesson 4: Exposure and Stops

In previous lessons we have talked about the basic theory of how a camera works, including some basic optics, and introduced the idea of exposure and how we control it with the exposure triangle. In this lesson we will be drawing upon what we have learned to understand the first point on the exposure triangle – aperture – and how it works to create your photo.


Aperture animation

Fig 1.5.1 The iris opens and closes to change the aperture.
Based on (source-

The word aperture simply means “an opening” ( In the case of photography, the aperture is created by an adjustable iris that can be opened or closed to control how much light enters the camera. This iris is made of a series of thin metal blades that move together to create a roughly circular opening of variable size. In most DSLR cameras, the iris is built into the lens itself. It is the opening in this iris that is actually the aperture.

When adjusting the size of the aperture, we describe “opening” the aperture up and “stopping” it down. That simply refers to making the hole wider or narrower. A photographer may say they are “shooting wide”, meaning they have opened the aperture a lot, or they may say they are “stopped way down”, meaning the aperture has been closed a lot.

f ratio revisited

In Lesson 3, we discussed the f ratio, and described that as the focal length of the lens divided by its diameter. This is the focal ratio. For a single lens, the f ratio is always the same. However, with our adjustable aperture, we can do a very neat trick. The aperture acts on the lens as if it is cutting away the part of the lens which is covered. So as we stop down the aperture, we effectively make the lens smaller, and thus change the f ratio of the lens. As such, the size of the aperture is described by the f ratio that it creates. A wide aperture may be f2.8, a narrow aperture may be f22.

As we discussed in lesson four, we measure the change in exposure with stops – a doubling or halving of the light, and fractions of stops. As such, the same measure applies to aperture. To double the light getting through a lens, we need to double the area of that lens which is uncovered. The area of a circle is determined by the formula πr2, so a doubling of the area increases the diameter by approximately 1.41. From this figure we get the sequence of f ratios:

The f ratio sequence in stops.
1 – 1.4 – 2 – 2.8 – 4 – 5.6 – 8 – 11 – 16 – 22 – 32

Depth of Field

A narrower aperture has a much greater depth of field.

Fig 1.5.2 A narrower aperture has a much greater depth of field.

If we look again at the exposure triangle diagram in lesson 4, you’ll see that the aperture influences the depth of field. The depth of field is the region of the photo which is in focus when the image is captured. It is a range of distance from the camera where objects look to be in focus. Aperture influences the depth of field by widening or narrowing this range, thus bringing more or less of the photo into focus, based on its distance from the camera.

Recalling what we learned back in lesson 1, the larger the hole that the light passes through a pinhole camera, the blurrier the image will be. When a lens is added to the camera, the image can be brought into focus, no matter the size of the hole, however, objects just either side of the focus point will be affected. If the hole, or aperture, is large, only objects very close to the focus point will be in focus. If the aperture is small, then the depth of the focus field is much wider, and more remote objects will be in focus.

Depth of Field can be pretty complex when you look deeply into it (such as: hyperfocal distance, airy discs and diffraction), but for an introductory course, the most important thing to remember is that a wide aperture (low value) means a shallow depth of field with less in focus and a narrow aperture (large value) means a broad depth of field with more in focus. We may return to discuss the more complicated issues in a future course.


Pastel bee
Creative use of DOF isolates subject from background.
Photo: annia316 used under CC license
While My Guitar Gently Weeps
The highlights on the strings clearly shows the changing DOF.
Photo: Paul J. S. used under CC license

Reflections on the Artic Sea
A narrow aperture gives a very wide depth of field.
Photo: wili_hybrid used under CC license
Lupins by the Lake
These images show focus from the closest objects to the horizon.
Photo: Neil creek all rights reserved.


  • Find a scene with interesting stuff at many distances from you. Photograph the scene with different apertures (keeping the photo exposed correctly by changing shutter speed), and see the difference in the depth of field.
  • Find a small subject that stands against a background a few meters away, like a flower. Try adjusting the aperture to isolate the subject from the background with depth of field.
  • Find a view. Try and photograph a vista with something in the foreground, such as a rock at a lookout. Try and adjust the aperture to keep the whole photo in focus.


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Neil Creek is a professional photographer from Melbourne, Australia. He has been shooting with a DSLR since 2004, and blogging about his experiences since 2006. Neil has authored five ebooks and a video training course, all designed to help others improve their photography. View Neil's folio at his home page. Learn about his publications here.

Some Older Comments

  • Alicia June 26, 2011 12:13 pm

    I can tell you are an awesome teacher! Thanks!

  • David August 23, 2009 02:30 am

    I know that this is well past when you wrote these articles, but I have a homework submission :)

    I really enjoy playing around with depth of field, and am learning how to transfer my idea of what i want into what I get.

    I had been out trying my hand at some macro photography, when I was heading home and decided to get a quick picture of a sunflower I saw. Being to lazy to change out my macro lens for another, I just stepped back a little ways, and came out with my current favorite photo of all of them I've taken.

  • sanjay pratap August 21, 2009 08:04 pm

    remarkable,very informative and best example i have ever seen on such a complex topic.
    Thanks a ton Niel

  • Barbie April 10, 2009 11:37 pm

    I love this site.......the articles regarding aperture have been FANTASTIC!!! Thank you!!! I shoot everything from macro with extension tubes to "landscapes" at the beach. I never had schooling and before my Canon 300D I didn't know what to shoot with but a 110. As I have "grown" I felt like some one gave me a bag of flour, sugar, salt, eggs, milk and vanilla and then said "ok, go make a cake" I had all the ingredients but had no clue as to how much of each to make the flavor of cake I had imagined.

    I love the triangle concept........mine is more of a square.....ISO, aperture, shutter speed and light setting. I almost never shoot with auto white balance anymore.

    Your sight is so user friendly and answers so many the pic examples too.....visuals are a good teachng tool.

    Thumbs up people!!!

  • starrpoint February 18, 2009 02:28 am

    This is a great explaination in plain language.
    I do wish you had a print setting so I could read it over and over.until I completely understand it.

  • Paul A. Orosco February 17, 2009 12:00 pm

    Thank you for some excellent basic simple tips. They are really helpful to me.


    From: Paul in Okmulgee, Oklahoma

  • Sunmag February 16, 2009 03:47 am

    Thats a quite a lot of Information on DOF, i tried this and understood what DOF is, need to try more and experiment on this...

  • joel February 14, 2009 12:01 pm

    they made me a pink snowflake?! hmmm...

  • joel February 14, 2009 12:01 pm


    Those are great articles. Thank you very much.

  • Samantha February 14, 2009 06:08 am

    I enjoyed the article, I helps alot. It is mind blowing sometimes but I still trying to grasp the concept of how everything works together to get different effects.
    Thanks for the info!!

  • joyce February 13, 2009 09:18 pm

    Thanks a lot for the very clear explanations.
    Would it be possible to obtain a printable version?

  • Vikki February 13, 2009 02:00 pm

    I just got my camera two weeks ago.... been reading books, and am going to a beginner workshop in L.A. this weekend, but these lessons have really given me a jump start!
    Thank you so much for sharing your knowledge!!!
    The examples and homework are great.

  • Chuck C February 13, 2009 11:05 am

    Since retiring, I have come to LOVE photography. These wonderful articles keep me busy working to understand how to get what I want in photographs.

  • soma February 13, 2009 04:31 am

    I never leave a comment, but this article is so good I had to let go of my inertia.

  • Chuck February 13, 2009 03:34 am

    Wow. This is a great article. I got my son a DSLR for Christmas and he has been eating these articles up, as have I.

  • Perry February 13, 2009 02:52 am

    What a great lesson! I had finally figured out shutter speed and aperture and their relationship recently. Took me a while, but finally got it. Always good to have it reinforced, though!

    Can't wait for the summer to take my dSLR and all my new knowledge to Glacier National Park

  • Richard Schulz February 13, 2009 02:46 am

    OK, I've known about aperture and depth of field since I was fifteen but what were those other things you mentioned? Hyperwhat? I have found that by doing these tutorials it keeps me going back to basics and not taking my shooting for granted. It makes me think. Thank you.

  • LisaNewton February 13, 2009 02:18 am

    Wow, what a great lesson. I wish I'd seen this yesterday before I took my long distance shots from the top of the mountain. Now, I'll have to do another hike to see the difference in the photos.

    Love, love, love the various graphics you used to demonstrate your points, Neil.

  • donna February 13, 2009 01:59 am

    this is fabulous - and i'm going back to read from lesson 1 !

  • rohitj February 13, 2009 01:27 am

    The photo (by wili hybrid) shown for narrow aperture is actually taken at f/9. Do you think its still narrow aperture?

  • Aimee February 13, 2009 01:25 am

    This is great, loved the examples! What's the best aperture to get a scene like the lower ones.. how much difference does f8 compared to f22 make?

  • Lee Milthorpe February 13, 2009 01:10 am

    Totally agree with Ed, this is so in depth but easy to understand, even as a beginner!

    Great article Neil!

  • tyler February 13, 2009 01:03 am

    This is concise, and the samples are good. Well done.

  • Erin February 13, 2009 12:43 am

    The images in this post are so helpful. I've just been reading Understanding Exposure by Bryan Peterson. This article plus that book have increased by knowledge by 100 times in the past two days!

  • Ed O'Keeffe February 13, 2009 12:24 am

    This is one of the best explanations of cameras aperture and depth of field - thanks for sharing your knowledge with us.