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.
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:
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.