As technology continues to advance DSLR camera bodies have a shorter useful life as, on average, most photo enthusiast and professionals upgrade their camera bodies every two years. Lenses on the other hand, if properly maintained, having a lifespan approximately 20 years, have more longevity. How does this translates to you the consumer? As long as you maintain your loyalty to a specific camera brand your lenses can be used with all compatible camera bodies. Your optics are ultimately most important, the better quality the lens, the better quality your images. With this in mind, it would be wise for you to invest in the best quality lens you can afford.

Selecting the right lens is important. Start by considering the type of photography you like to create.  Sports/Action, Landscapes, Portraits, Small Product. There are basically two types of lenses, tele-zoom and fixed/prime.

Tele-zoom/telephoto lenses are commonly used to provide you a wide range of focal-lengths. Example being a 16-300mm lens, which may have a range of f 3.5 at 16mm and f 5.6 at 300mm. The pro to using a tele-zoom lens is it will allow you to carry one lens with you instead of having to pack a myriad of lenses. The con is they generally are slower and do not allow a lot of light in causing you to shoot with slower speeds. They do make faster tele-zoom lenses, however, they generally designed with the professional in mind and are more expensive.

Fixed focal length lenses have only one focal length are more commonly referred to as prime lenses. The pro is they are faster lenses (1.4, 1.8, 2.4, 2.8). The con of a prime lens is that it is limited to one focal length (18mm, 24mm, 50mm, 60mm, 85mm, etc) and are generally more expensive.

Which lens is for me?  If you like to shoot sports and/or create images under darker, not so bright situations, you will want to select the fastest lens you can afford. Fast lenses offer a wider aperture opening. If you prefer to shoot landscapes and macro/close-up images of flowers or small products you will want a lenses that offer smaller aperture openings requiring the use of more light which create overall sharper images. Most portraits are created using longer focal lengths ranging from 85 to 200mm and f-stops ranging from f4.5 to f8

What do lenses control?  Most people think they control how much light is let into their camera, and they’d only be partially correct.  The lens you use actually control two things, Depth of Field and Background perspective.

What is Depth of Field? While in fact the amount of light the lens opening, Aperture, allows to pass through the lens to either the film or sensor plane.  It’s a combination of three factors that determine the depth of field of an image: The focal length of your lens, the f-stop (aperture) you select, and, the distance between your lens and the subject you are photographing. Depth of Field is the actual distance or zone of what is actually in focus.

For instance, if you were to use a Canon EOS  T5i body and an 85mm lens at f5.6 and are 10 feet from your subject everything from 9.58 feet to 10.5 feet will be in focus.

Focus at the subject distance, 10 ft at f5.6
	0.88 ft
9.58 ft		10.5 ft

By simply changing your aperture setting to f11 you will increase your depth of field almost 3/4 of a foot, so everything from 9.19 feet to 11 feet will now be in focus.

Focus at the subject distance,10 ft at f11
	1.78 ft
9.19 ft		11 ft

Now if you keep your aperture set at f11 and step back 5 feet further away to 15 feet from your subject you will nearly double the depth of field. The result is everything from 13.2 feet to 17.3 feet will now be in focus.

Focus at the subject distance, 15 ft at f11
	4.08 ft
13.2 ft		17.3 ft

Think of the aperture as you do your iris. Wider aperture openings allow more light in which allow you to create images with a faster shutter speed, while smaller openings make things sharper (its why you squint when you want to see something sharper) and require a slower shutter speed. Depth of field changes as you change your aperture.  Notwithstanding the above, you have shallow depth of field (less is in focus) with a wider the lens opening, while a smaller aperture setting will yield a greater depth of field (more is in focus). A less complex way to remember how to control depth of field using your aperture settings is, the lower your f-number, the smaller your depth of field. Likewise, the higher your f-number, the greater your depth of field.

Background perspective changes as your focal lengths changes. The wider angle (focal length) your lens the more of the background you are going to see. Conversely the longer the focal length the less of the background you are going to see.  The effect of using a longer lens with a greater focal length is commonly referred to as compressing your background. Note the diagram below demonstrates camera points with specific focal lengths. The images are framed so the edges will touch your subjects shoulders which result in noticeable differences in the view-able background.

Larmon offers Canon, Nikon and Tamron lenses in the store. Stop by for a visit to check them out and speak with one of our experts. Larmon also offers Sigma and Sony lenses online at larmonphoto.com.   Larmon U offers private one-on-one mentoring. Call Larmon at 215-887-1248 or click here to register for private mentoring if you are interested in learning more about lenses and how to control depth of field with you camera and existing lenses.