Camera Samurai

I was talking to my friend Johanna today about photography and f-stops. I think I was keeping her from her work but she didn’t seem to mind too much, at least for a few minutes. Johanna is a great photographer who is still learning photography theory, as we all are, and said she has a hard time with f-stops.

Truth be told, I think everyone has a hard time with f-stops until they hear the theory for the fiftieth time and do some practice runs, experimenting with the camera settings. I will include an exercise at the bottom of this post, in case you want to play with your camera and experiment a little.

So here’s how f-stops work. The f-stop on your lens is the ratio of the focal length to the aperture. Get it? Good. Okay, seriously – let’s look at it another way.

f-stop = focal length (mm) / aperture (mm)

Remember: the aperture is the actual hole through which light passes, whose size you control by using the f-stop ring.

Okay, that’s cool and all, but what do the f-stop numbers really mean?
You got me there. Maybe I was being too technical. The small number f-stop means you have a big aperture and thus more light coming through. A big f-stop number means a smaller hole and less light coming through.

So f-stop and aperture size have an inverse relationship. Let’s plug in some real numbers and see what we get.

Note that the focal length stays the same. That’s because you have to keep one element constant to perform this calculation and even with zoom lenses you can only shoot at one zoom setting at a time. You can see that as the f-stop number gets bigger, the aperture gets smaller and vice-versa.

Okay – so what does all this mean?
The f-stop refers to how much light you are letting in. This will affect your shutter speed by allowing you to shorten or lengthen exposure time, depending on how much light is getting in. Back in the day we had to calculate this by hand. Really we did it in our heads because we were dealing with fractions of a second and those of us who are lucky do not have fractions of fingers to count on. Now we have fancy computer-controlled cameras that do all the hard work for us. Thank goodness for that!

Other effects of f-stops
The f-stop also controls your depth of field. Depth of field refers to how much stuff is in focus in front of and behind the primary subject you focus on. A small number f-stop allows more to be in focus and a small number f-stop makes less stuff in focus. Look at these examples. The first one was shot at f22 and the second at f5.6.

The picture shot at f22 shows many more fence posts in focus than the f5.6 picture does.

Assignment
Play with your camera! Do something like I did in the above photos. Take photos of a series or group of objects. Focus on the same element each time and change your f-stop so you can get different effects and get a feel for how f-stop affects the depth of field in your pictures. Experiment! Learn! Have fun!

Post your results in the Camera Samurai Flickr Group.

Technorati Tags: photography, f-stop, experiment, ratio, focal length, aperture, inverse relationship, depth of field

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