ODL101: Aperture

Today, I went on a little photo adventure to demonstrate the next parameter of exposure: aperture.

One thing to note if you’re looking to get into photography, especially street photography, is that people can be mistrustful of cameras. Be prepared to be engaged by people who are curious about what you’re doing. Some will simply be politely ask what you’re up to, while others will come across a little more aggressive. I ran into both kinds on my little photo journey yesterday morning.

Reentry into the Abstract. October 2017. (Canon 60D, EF 100mm f/2.8 Macro USM; ISO 200|100m|f/5.6|1/125)

I set a timer for 10 minutes on my phone, got in my car and just drove. For every red light or stop sign I hit, I flipped a coin. Heads I turned left, tails I turned right. When my timer rang, I ended up next to a day care (or so I thought) in a quiet little neighborhood (or so I thought).

Only a few passers-by asked questions, and I went about my photography business with few interruptions. I was then approached by the director of the school across the street from where I was parked (oops…) and, after a short introduction, we had a wonderful talk about life and the state of the country.

After she left, I went back to work, but, mere moments later, a man (whose home I was parked outside of) rudely asked me to leave. That’s just how it goes sometimes. (You’ll likely get less attention out in more openly public places than I did this morning, but just be aware that confrontation can and will happen!)

So I left… but not before snapping some pictures to help demonstrate today’s lesson.

Barbed Wire. October 2017. (Canon 60D, EF 100mm f/2.8 Macro USM; ISO 100|100m|f/5.6|1/1250)

Aperture is the opening in your camera that allows light to hit your sensor. Shutter speed determines how long the shutter remains open, while aperture determines the rate at which light gets through.

That means, the bigger your aperture, the less time you need for what is called equivalent exposure. The inverse is also true!

Aperture size is denoted as a fraction, and is referred to as an f-stop. You will find this notated as f/4, f/8, f/11,etc.. The f in f-stop refers to focal length, and the fraction is determined by dividing the focal length of the lens by the size of the opening in the lens that lets light through (your aperture is controlled by a diaphragm that opens and closes).

What’s important to note here, is because f-stop is written as a fraction, lower numbers mean a bigger aperture, which, in turn, means more light!

f-stop is therefore a quantitative measure of what is referred to as “lens speed.” Lens with a lower f-stop are considered “fast lenses” because they have large apertures, which allow for faster shutter speeds. Everything is related!

The first concept that we need to understand, in regards to using our aperture sizes to take better pictures, is that of “depth of field.”

Depth of field is the distance measure between the nearest in focus object and farthest in focus object. Having a wide or narrow depth of field is desirable depending on your intent.

The easiest way to understand depth of field is demonstrate it:

bikeDOFdemo_0000_Layer 2
Abandoned Bike DoF Test. October 2017. (Canon 60D, EF 100mm f/2.8 Macro USM; ISO 100|100m|f/13|1/160)
bikeDOFdemo_0001_Layer 1
Abandoned Bike DoF Test. October 2017. (Canon 60D, EF 100mm f/2.8 Macro USM; ISO 100|100m|f/2.8|1/2500)
bikeDOFdemo_0000_Layer 2-Edit.jpg
Abandoned Bike DoF Test, DoF Highlight. October 2017. (Canon 60D, EF 100mm f/2.8 Macro USM; ISO 100|100m|f/13|1/160)
bikeDOFdemo_0001_Layer 1-Edit.jpg
Abandoned Bike DoF Test, DoF Highlight. October 2017. (Canon 60D, EF 100mm f/2.8 Macro USM; ISO 100|100m|f/2.8|1/2500)

The blur caused by out of focus areas is called “bokeh.” Bokeh is a desired artistic effect, and can be used to better isolate your subject.

The quality of bokeh is directly affected by your depth of field. Take a look at the following video to see the difference between f/2.8 and f/13:

Notice how, at a wide aperture (f/2.8), the depth of field is so shallow not even the entire rose is in focus. At this point, the background is blurred enough that it is difficult to make out individual leaves.

Then, watch as the background slowly comes more and more into focus as the aperture narrows. At the end of the video, the aperture is small enough (f/13), that the background is entirely recognizable. With a small enough aperture setting, the entire background would be in focus.

Between shutter speed and aperture, you can control the parameters which will have the most direct impact in your everyday photography.

Remember, smaller apertures mean less light, and bigger apertures mean more light! Both can be balanced out by shutter speed! Use this knowledge, plus your knowledge from the shutter speed lesson to take better pictures!

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