Photo Tips: Understanding f-stop to control depth of field


In photography, if you want to blur the background and lead your viewer’s eyes to the subject you must understand how to use the f-stop. The f-stop controls depth of field, how much of the photo is in focus. Although composition is always the most important feature of a photograph, depth of field is right up there. Composition is relatively simple. Understanding the f-stop, however, is a different story.

My explanation of the loony f-stop number

f-stop is the number assigned to the aperture opening of your lens, but the reasoning behind the number seems confusing to most. You might think that the bigger the number – say f/22 – the more light is let in, but no, they have to make you think a bit. The shutter speed works in a more reasonable fashion: The larger the number the faster the speed. However, the f-stop is opposite: The larger the number the smaller the opening.

Think of it like this: When you squint to see something better, you block out some light to focus on a smaller area.

f-stop photo tips
Flower at Marimurtra gardens

So the larger the number, the more more depth of field, so more of the picture will be in focus. Notice the picture above, shot at f/6.5: The background is blurred and the flower is in focus. Using smaller f-stop numbers will focus attention on the subject. In photographing people, nature and other subjects you want less depth of field.

In contrast, notice the difference in this picture:

f-stop photo tips
Beautiful stone steps lead to other areas of the garden

The f-stop is set to f/10 and focus is a third of the way up the stairs. This allowed the stonework to stay crisp and sharp throughout the photo.

Remember: Greater number=more of the picture is in focus. Lower number=less in focus.

Tip of the week:

  • When taking pictures during travels, take several of the same subject and play with the f-stop. This will capture a variety of depths of field and will give you a variety of images to choose from when you get home.

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Written by Dan

Professional photographer specializing in street, food and travel shots at As We Saw It travel blog. “Photography is unique in that it captures light in all forms, and since the Bible says YHVH (God) is light, photography captures Him in many forms.”

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