An Introduction to Aperture

The last few weeks I wrote about the first two components of the exposure triangle (ISO and Shutter Speed).  This week I will be writing about the final component - Aperture. 

So what is the Aperture’s function?  Well it’s basically the opening inside your lens and its purpose is to regulate the amount of light that enters your camera’s sensors.  Each lens will have a maximum and minimum aperture that it can open up to.  Your camera lens will indicate your maximum aperture right next to your lenses focal length (i.e., 55mm f/1.4).  If you look at your lens, you will notice that the minimum aperture is not listed.  You would need to find this information out from your camera’s manual.  Aperture is measured in f-stops. Listed below is a picture of a sample of f-stop sizes from the Wikipedia website.

Source:  http://en.wikipedia.org/wiki/F-number

 

So do you notice anything funny about the numbers above?  Well the one thing that confused me in the beginning was the correlation between the size of the opening and the f-stop number.  Notice that the largest opening is indicated by f/1.4 and the smallest opening is an f/8.  You would think that the larger number would equal the larger opening; however, it is the exact opposite.  So important items to note are:

1.       Smaller number = larger opening

2.       Larger number = smaller opening

3.     In low light situations you would want to use a larger opening in order to let in  more light (i.e., 1.4, 2.8 or 3.5 depending on your lens)

4.     In highly lit areas such as outdoors you should be able to shoot with a smaller opening but this could change if you want to be artistic with your photos which leads me into my next discussion.

Depth of Field

Understanding the depth of field is a very important because this is how you can control what parts of the photo should be sharp and what parts of the photo should be out of focus/blurry.  Many photographers adjust their aperture for depth of field in order to get those nice blurry backgrounds also known as “bokeh”.  Unfortunately, your camera is not going to be able to know exactly what people to keep in focus on its own.  For example, you may be taking a group photo and you would like everyone in focus but what if you are at an amusement park and there are people everywhere.  Do you want those people in the background in focus for your photo?  How can the camera determine that?  Well by adjusting your aperture you can be in control. 

Below are some important things to note about Depth of Field.

1.      The people/objects located in the depth of field will be sharp

2.      The people/objects outside of the depth of field will be blurry and out of focus.

3.      The larger the opening (smaller number) the smaller the depth of field

4.      The smaller the opening (larger number) the larger the depth of field

In other words, if you want a blurry background you should use a larger opening/smaller depth of field.  If you are taking a family group photo and want everyone in focus you would use a smaller opening/larger depth of field.  So when deciding on your Aperture setting you need to think about the following:

1.    What people/objects do I want crisp and in focus?  For example, if I were shooting a group shot, I would use an f-stop of 5.6 or higher.

2.    Do I want a bokeh “blurry” background?  For example, shooting a close-up, I would most likely use a 2.8 f/stop.  Blurry backgrounds come in handy when you have an unpleasant background such as a parking lot.

Here are some pictures that I took to display the difference in Apertures.

The following photo was taken with a smaller aperture (larger number f/5.6) – notice that everything in the photo is sharp including the photo on the mantle.



The photo below of my sister-n-laws dog was taken in front of her garage, so I used a 2.8 aperture in order to blur the background.

I blurred the background on the group photo in order keep the cars in the parking lot out of focus.

So what’s your preference?  Do you like those blurry backgrounds or do you prefer all the details?   I would love to hear your comments.