Zoom Into Focal Length

The term “focal length” is one of those photography terms that never really made sense to me.  Wikipedia defines focal length as:

The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. A system with a shorter focal length has greater optical power than one with a long focal length; that is, it bends the rays more sharply, bringing them to a focus in a shorter distance.

Now that we got that out of the way, what does it mean to a camera operator?  It is a measure of magnification and angle of view.  It is often thought of as number that represents how much we zoom in or zoom out.

I found this diagram on the internet which does a great job of showing the range of wide angle through telephoto lenses and the associated focal lengths.  Most digital SLR cameras come with a lens that will zoom between around 30 mm and135 mm gives some wide angle capability through a moderate amount of telephoto.

Focal Length and Telling the Story

Beyond the simple description of focal length and the ability to zoom in and zoom out.  There are a few more subtle details that make a huge difference.  Using the famous barn on Mormon Row near Grand Teton National Park.  Here are some examples:

This wide angle view gives a broad view of the scene.  It brings many objects into the picture but doesn’t focus on any one object.  Wide angle shots increase the apparent space between objects in the foreground and in the background.  This is a nice picture that gives a big-picture view of the environment.

Wide angle shots can be cropped to give the appearance of a panoramic.  As long as the image is not going to be enlarged too much, this can be a great option.

Increasing the focal length as shown below opens the opportunity to make individual objects more prominent.  The barn and the mountains share the focus of this picture and their relationship is a major theme of the picture.  It is easy for the viewer to start connecting with the barn and begin to imagine life back in the day.  There is plenty left to the imagination and this image tends to trigger that imagination.

In stark contrast to the wide angle view, the telephoto shot shown below dials in on the barn.  This intimacy goes all the way down to the texture and vibrance in the wood.  The corral fence becomes a part of interest and the mountains appear much larger with respect to the barn.  Additionally, the distance between the barn and the mountains appear much more compressed than the wide angle view.

Zooming in further continues to narrow the field of view.  Had this picture been taken at around 300 mm, only a portion of the barn would be captured in the frame and the mountains would barely be recognizable (as is indicated inside the red box)

Even though the pictures above were taken from the same spot, the different focal lengths significantly change the feel to the point that they are three completely different shots with three completely different personalities.

Taking pictures using large focal lengths tends to compress objects in range.  The first picture of the guard stations makes it appear that these stations are positioned very close to each other.  The second picture puts the actual spacing in perspective.

Using large focal lengths to capture wildlife is often a necessity since you often can’t, or shouldn’t, get any closer.  In addition to the increased magnification, the narrow field of view can create a greater sense of intimacy that can’t be achieved with a smaller focal length.  This works with taking pictures of people as well.  We often tend to want to take pictures of people from about 10 feet away, the standard point-and-shoot shot.  Backing up and zooming in can produce some great shots with very candid facial expressions, particularly if they weren’t aware you were snapping the shot.

Focal Length and Depth of Focus

In addition to f-stop affecting depth of focus, focal length plays a significant role in depth of focus.  The greater the focal length, the less the depth of focus.  Stated another way, the more you zoom in, the less objects in the background will be in focus.  As noted below, the image of the flower on the right taken at a focal length of 300 mm cannot maintain the entire flower in focus, the background is completely blurred out.

The ability to zoom in at the higher focal length creates some neat opportunities, particularly in wildlife photography.  One challenge that comes along at the higher focal lengths is the limited angle of view causing the slightest lens or subject movement when the picture is taken to be much more exaggerated.  Sturdy tripods and fast shutter speeds help reduce this undesired byproduct of greater magnification.

This post highlights a couple examples of how focal length affects the outcome of an image.  Focal length is easy to experiment with in the field.  Take several shots at varying focal lengths and see what comes out!

Enjoy!!

Disclaimer.  The goal of this site is to encourage others to get outdoors and experience what life has to offer.  Since photography is a central theme of this site, I thought it might be helpful to include a few tips and ideas for understanding the basics of photography.  Most of what I offer in the photo tips section is based off experience I have gained over many years of enjoying photography and experimenting with different camera settings.  This trial-and-error approach to learning photography has certainly been supplemented with tidbits of techniques gained from a variety of photography-based magazines and talking to other photographers.  While I would love to give credit to the sources, I didn’t keep the magazines and can’t remember what I learned from who.  Having said that, these tips are pretty basic and would be considered common knowledge by photographers.