Posted on by & filed under Photography.

As a photographer I cannot emphasize the importance of having a solid understanding of how Aperture and depth of field are related.

In a previous article (F-Stop is NOT an F-word) I explained the nomenclature commonly used for aperture is f-stop. Aperture and f-stop relate to the size of the lens opening.

As one of the three components of an exposure (shutter speed, lens aperture, ISO) aperture plays a vital role.

The primary use of aperture is to control the depth of field (the distance in front of and behind the subject that is in apparent focus) of a photograph and  in part control the amount of light that is allowed to enter the camera through the lens. Ever see the subject in complete focus against a fuzzy background (bokeh)? The photographer used a large aperature (smaller f stop) to create that creamy background that makes the main subject of a photograph really stand out.

Also from the article (F-Stop is NOT an F-word) we discussed that the bigger the aperture/f-number is the smaller the opening which in turn results in a larger depth of field. If you were to set your lens to its biggest number the lens would be “fully stopped down”. Conversely,  if you were to set your lens to its smallest number the lens would be “wide open”.

Now, having said all that let me  also say the depth of field is not sharpness. What I mean by this is that just because you have a large depth of field doesn’t mean that the subject or subjects will be sharp.

Apparent sharpness can be influenced by factors that have nothing or little to do with depth of field, such as lens quality, dirty sensor or lens element, fog or haze in the environment, even down to camera shake during long exposures.

So if you want good separation of your subject from the back ground, set your aperture to a smaller number. Then, continue to adjust your aperture up or down until you get the desired results.

Below is a diagram showing the comparative size of full f-stop apertures.

©R. Mabry Photography

©R. Mabry Photography

As you can see from the below image series aperture is a powerful tool in your photographic arsenal. These  photos were shot using a Canon EF 70 – 200mm f/2.8L IS USM lens.

©R. Mabry Photography

©R. Mabry Photography

About the Author

Ray Mabry has over twenty years experience in photography. He started in film and used black and white to capture images in architecture, landscape and abstract forms. In 2001 Ray, with his extensive computer technology and digital imagery experience, made a natural and seamless migration to digital. Whether shooting film or digital, Ray loves the freedom of creative expression that photography has to offer.

Ray has a professional photography studio,, runs a blog and also co-organizes a Meetup group called the Sonoma County Photography Group,

Tags: Aperture, background blur, bokeh, Canon lens, Depth of field, Digital Photography, f-stop, Focus, Fully stopped down, fuzzy background in photograph, Wide open,

3 Responses to “Understand How Aperature and Depth of Field Are Related”

  1. Rose

    Hi Ray,

    I was wondering if you wouldn’t mind giving me your opinion about a couple of things? I would like to get more into portrait photography. I have a Canon 70-200mm f/2.8 and that works great when I have lots of space. But, what do you recommend for portraits in smaller spaces? Also, what would you recommend for shooting events in low light situations?

    I hope that your answer points me to Canon’s EF-S 17-55 f/2.8 IS USM But is 55mm a good length? Is there an “off” brand that is just as good but less expensive? I’m partial to Canon products.

    This is what I have in my lineup thus far:

    • Canon 50D body
    • Canon 28-135 f/3.5
    • Canon 70-200 f/2.8
    • Sigma 150-500 f/5-6.3

    And, finally, if I wanted to start out doing in studio (or in home) photography, what lighting would you recommend? I have a softbox right now but haven’t had much time to play with it. I also have a speedlite 430. Is that enough to get started?

    And, my last question, if you don’t mind, what type and size of backdrop system do you recommend? And, what type of material for the backdrop?

    Thank you so much!!


  2. R. Mabry Photography


    A good range for portrait photography is somewhere between 85mm and 105mm and between f3.5 and f5.6 and sometimes f8 depending on the background and the lens. But that is just a rule of thumb. Breaking the rules is where all the fun is.

    From you list of gear it look like you have everything you need for portrait photography. Your lenses are perfect for it. I use my Canon 70-200 f/2.8 for 90% of my portraits. The other 10%, like for large groups, I use my Canon 24-70 f/2.8. Canon has a new 85mm lens that is the best for portraits, but it’s around 2 grand and who can afford that. Your Canon 28-135 is a fantastic portrait lens as well as your Canon 70-200.

    Canon’s EF-S 17-55 f/2.8 IS USM is a wonderful lens but a little on the low side for portraits. But again, breaking the rules is always an options.

    For off brand lenses Sigma or Tamron are your best bets. Sigma being preferred over Tamron (just a personal preference).

    As for lighting, if you are going to use a flash of some kind you will defiantly need to use a soft box, umbrella or some type of diffuser.

    There are so many new materials out there for backdrops. I prefer muslin for my backdrops whenever possible. I have several if you would like to borrow one to play with. I also have different sizes some small and 2 really large ones for draping.

    Feel free to call me if you want to talk about all this. I love talking photography.

    I hope this helps.