Aperture: How It Affects Your Photography & Why You Should Care

Aperture diaphragm, Canon 70-200 mm f2.8 lens.  (Copyright 2010 / Andrew Boyd)

Aperture diaphragm, Canon 70-200 mm f2.8 lens. (Copyright 2010 / Andrew Boyd)

[Note: I'm bringing this post 'back to the front' because it's on my list of essential-that-you-know-this stuff for beginning shooters. Originally published in March of 2010, the information about aperture and depth of field is all still up-to-date and relevant. --/DiscerningPhotog]

Aperture: Now there’s a real ‘Photography’ word! Do you understand what ‘aperture’ refers to and how it affects your photography? Here I’ll explain exactly what it is and why you should care.

Simply stated, “aperture” is the hole in your lens that allows light to pass through to your CCD (charge coupled device) during an actual digital camera exposure. The size of the hole has a big impact upon your photos.

So what does this mean for your shooting?

Let’s start with how aperture works in your lens/camera setup.

If you’ve ever taken a lens off of a DSLR, held it up to a light and looked through it, the ‘default’ position that the lens will be in is at the largest, maximum aperture(sometimes even larger than the maximum aperture). If you’re looking through a 200mm f4 lens, for instance, then the wide-open hole will correlate with the ‘f4’ position on the camera. This f4 position will let the most light in, and also be the position with the shallowest depth of field. This just means that except for your point of focus, most of the other elements within your composition will tend to be out of focus. (‘Bokeh’ photography is all about this type of shallow depth of field shooting.)

Higher f-stop numbers correspond to smaller aperture holes: f2.8 or f4 will be a relatively large aperture (hole), while f11 or f16 will be a much smaller hole.

With a modern DSLR, you can see this by stopping your lens down to f8 or f11, then peering through the front element and pushing in the depth-of-field preview button. You’ll see the wide-open aperture hole suddenly contract down to a much smaller octagonal shape.

Try different f-stop numbers and you’ll quickly get a sense of how this works.

How does this affect your images? As you stop the lens down, say to f8 or f11, the hole gets smaller, and more things in front and behind your point of focus will appear sharp in your photograph. So large apertures = shallow depth of field; small apertures equal larger depth of field in your photograph. This can be a good thing or a bad thing, depending upon the photo you’re trying to shoot. The trick is learning to be in control of this phenomenon.

To really start to see how this can work, I suggest you operate your camera in a fully manual mode. As you change the aperture, making it larger or smaller, you’ll need to make a corresponding change to the shutter speed you’re using, since these two adjustments are dynamic and always work together. For instance, if your exposure is 1/125 sec @ f 8 and you want a shallower depth of field, you’ll need to open up the aperture, say to f2.8 or f4. Since you’re now letting all of that extra light into the exposure, you’ll need to increase the shutter speed to compensate and keep the overall exposure correct. I’ll address the creative and critical importance of shutter speed in another post, but for now, just use your camera meter to make the correct adjustment when changing the aperture.

Image at left is shot at f2.8, the image at right at f14. (Copyright 2010 / Andrew Boyd)

Image at left is shot at f2.8, the image at right at f14. (Copyright 2010 / Andrew Boyd)

I have some examples here that illustrate how important this can be. In this first set of photographs, the image on the left was shot at 200mm with an aperture of 2.8. The background is thrown completely out of focus, allowing your eyes to immediately go straight to the faces and butterflies. In the second image, the focal length is still 200mm, but now the aperture is f14.  Suddenly all of the distracting detail in the background comes more into focus, in effect competing for your attention with the important foreground detail. So in this case, all of that depth of field would be a mistake, ruining an otherwise decent image.

In the second set of images, the opposite is the case.  In the driftwood still life, more depth of field is a good thing.

Driftwood still life. Top photo is shot with my Canon 50mm Macro @f2.5, the bottom photo @f11. The extra depth of field greatly improves this composition. (Copyright 2010 / Andrew Boyd)

Driftwood still life. Top photo is shot with my Canon 50mm Macro @f2.5, the bottom photo @f11. The extra depth of field greatly improves this composition. (Copyright 2010 / Andrew Boyd)

It helps to know that every time you move your aperture a full f-stop number, you are doubling or halving the amount of light the exposure will use. On older camera lenses, this was easy because the f-stops were the clicks on the lens barrel:

F1.4/f2.0/f2.8/f4/f5.6/f8/f11/f16/f22 was a normal sequence of f-stop numbers. So changing from f8 to f5.6 doubled the size of the aperture, allowing twice as much light in.

This is trickier with modern digital cameras, since most of them provide third-stop increments and there are no more clicks on a lens barrel: between f5.6 and f8, you’ll also have options for f6.3 and f7.1, for instance. Don’t worry about the actual, weird numbers, just know that these are third-stop increments on the f-stop continuum.

So go out and experiment with this yourself! Find images that benefit from the shallowest depth of field (sports action shots and wildlife are two that come to mind) and shoot them at the widest aperture possible. Now stop your lens way down to say f11 or f16, adjust your shutter speed accordingly, and shoot away. What happened? Were your new images better or worse than the originals? Which version worked? Try the same thing with something that needs lots of depth of field: a landscape, a field of flowers, maybe a still life. Shoot some images both with and without lots of depth of field. Which ones work better?  As you experiment and play around with aperture and depth of field, you’ll start to see how fundamental this is to all of your shooting.

Now get out and make some great images!

Hi, I’m Andrew Boyd, a.k.a. The Discerning Photographer, and I hope this post has been interesting and informative. Please leave me a comment about it, let me know what you’d like to see more of on the site! You can also sign up for email delivery of all future articles or my RSS feed. Thanks!–DiscerningPhotog

Related articles on the web:

Aperture, Shutter Speed & ISO at The Discerning Photographer

Depth of Field tutorial at CambidgeinColour.com

Six Tips for Controlling Depth of Field at Epic Edits

Nothing Could Be Finer at Serious Amateur Photography

Aperture, Shutter Speed and ISO at YourPhotoTips



Posted in: How To

About the Author:

Photographer, videographer and photo editor. Host and creator of The Discerning Photographer web site. Currently a Canon shooter.

17 Comments on "Aperture: How It Affects Your Photography & Why You Should Care"

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  1. Andy Gock says:

    Nice summarized posting there. I thought perhaps we could mention about diffraction limit and sharpness too, as some people could get confused and thinking shooting stopped down to the max will give them maximum sharpness :)

  2. Hmmmm. When I take the lens off of my Nikon DSLRs I will not see the largest opening, but the smallest one. There’s a small pin on it that opens and closes the aperture. Only when the lens is mounted on the camera the aperture opens all the way so that the viewfinder image will be as bright as possible.

    And… just IMHO… it is a whole lot easier to think of the aperture not as “the hole”, but of the fins (“curtains”) around that hole. The larger the curtain (f-stop number), the smaller the hole…

  3. You’re right, most modern lenses AREN’T at their sharpest stopped all the way down; I just didn’t want to get into this issue here in this ‘basics’ post. Thanks for your thoughts!

  4. Huh…shows my Canon roots, I guess. I haven’t shot Nikon in over 5 years and those lenses were still spring-driven for the aperture. My Canons do all of this electronically now and the widest aperture is what you see when you take the lens off.
    Anyway, thanks for your thoghts!

  5. Olamide says:

    I believe a larger aperture (Smaller f-number) gave a shallower depth of field than a smaller aperture.

    In your example with the butterflies however, you state that the image with the shallower DoF (Ieft) is taken at f2.8 while that with more DoF (right) is taken at f1.4 … Typo perhaps?

  6. Look closely…that f14, not f1.4.

    Andrew

  7. Salvador says:

    I work in the Industry Automation area nad I use cameras for BAR CODE reading.
    The camera remains fixed, always at the same distance from the lenses (more or less) and with the same lighting.

    Usually, when I read a tag, like in a medicine box, I don’t worry about aperture.

    But now, I intend to read a bar code that has the same size of the box (5 cm x 1cm).

    After reading your nice article I am not sure wich way would be better to distinguish the object from the background:

    a) to use a small f-stop number (f1.6 or f2) for a shallow depth of field and than the object in focus will be more distinguised from the background.
    OR
    b) to use a big f-stop number (f8 or f16) for more depth and the more focussed background will allow to better distinguish the object from the background.

    What would you suggest?

    Thank you in advance.

  8. Focus on the bar code, keep the f1.6 or f2 and the bar code will be in focus. This will throw the background out of focus too, which should help.

  9. Ashley says:

    I have always been the girl at the family gatherings or parties with a camera in my hands. I worked in a studio for about a year with nothing but my own self taught techniques and ended up with a very nice group of customers. What is your take on a photographer who is self taught rather than one who went to school for it? I started college but it was too costly and I have been called a hack for not finishing school. I am now doing free photo shoots to gain experience and learning all the joys my Canon has to offer. Competition in my town is fierce. I would think some of the best photographers were self taught so I would love you input on yhis matter :) Thanks

  10. Photography is all about the results, not the degree…but the degree can certainly open some doors. It depends upon what sort of photography you want to pursue. Recognize that it’s a tough, tough business, now more so than ever with the changes that the web has wrought…I think more and more people think that ‘anyone’ can be a photographer now, since digital has made everything so much more accessible. But ultimately it will be your images that determine how successful you are, nothing else.

  11. Rishav says:

    Hi Andrew,

    Thanks a lot for this amazing post! :)
    However, I have one question. Why is it that a larger aperture leads to a shallower depth of field? Shouldn’t it be the other way round? If more light enters, the background should be sharper, shouldn’t it?

  12. It’s just the result of how lenses actually work–smaller openings (apertures) will require longer times (shutter speeds) for enough light to hit the sensor to
    make the exposure; at the same time, smaller apertures create more depth of focus–thus greater depth of field.

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