First of all, the speed of the lens is determined by the size of the opening, known as the aperture. The larger the opening the faster the lens is considered to be. Typically, lenses marked with F4, F3.5, F2.8, and smaller are considered fast, while lenses marked with a bigger number are slower. I know this may sound odd, but the smaller the number the faster the lens. If you are new to shooting with an SLR camera, you are most likely looking at “zoom” lenses. Most zooms today have a variable aperture. This simply means that at the shortest end, the lens is faster than at the long end. For example, a typical lens a 28-80mm. This lens zooms from 28mm to 80mm, and it is a very good starter lens. This type of a lens will typically have a F3.5 aperture at 28mm (short end), while at 80mm (long end) it will be F4.5, or F5.6, which is considerably slower than the short end. Typically, the faster the lens, the more it will cost, and the heavier it will be. Most casual shooters look for very versatile lenses, and faster lenses certainly offer more flexibility in certain situations.
Now that we briefly discussed the concept of speed, lets figure out whether you really need a fast lens. The first thing that you have to think about is your shooting habits. Everyone is different, and very much unique. Some shoot landscapes, some only people, others night scenes, some shoot under water, and so forth. Typical casual shooter will likely shoot during daytime, and will likely be shooting portraits, landscapes, city scenes (during a vacation perhaps), and other fairly undemanding environments. If you shoot a lot of photos in dim light, like night clubs, restaurants, museums, outdoors after dark, and other dim light situations, a faster lens is definitely a boon. However, you should always keep in mind that most zoom lenses, while faster at the short end, will be slower at the long end. This is very important, because if are going to be shooting at the longer end of the lens, when shopping for a lens, keep this in mind, and you will save yourself some money. Let me explain. Take two lenses, one is a 28-80mm f2.8(short end) / f5.6(long end), and another lens, 28-80mm f3.5 / f 5.6. These two have an identical range, however the first is faster at the short end. This larger aperture does not come free. You may end up paying 2 times as much as the second lens. If you are going to be mostly zooming to the long end of the range, compare and price your lens at that end.
If you are going to be shooting mostly portraits and other static scenery and plan to use flash, or a tripod most of the time, you will not need a very fast lens, because the added speed will likely be of little benefit to you. As such, you will do just fine with a F4.0 or slower. Action shooters often benefit from faster lenses, and if you are planning to capture sports, animals, and other moving subjects, a faster lens may help at times. The single biggest benefit of a faster lens is the freedom it gives you, when the light is limited. If you are an action shooter, and capture a lot of action in dim light, the extra speed will be very helpful, and allow you more hand-held shooting. Always evaluate how much you are going to be shooting in different environments. Action and low light shooters will most benefit from lenses with apertures of F4.0, and larger. If you think low light, and action will be very infrequent, and you are comparing two similar lenses, choose the budget one, which will likely be just a bit slower. Often, a price of a zoom lens with just a slightly smaller aperture at the long end will be hundreds or dollars less than a similarly sized zoom with a slightly larger aperture.
Most modern Digital SLRs can really offset the need for a fast lens through higher ISO settings, something that Film cameras do by using a faster film. With Film cameras, you would need to switch a roll of film to change the ISO speed. If you use a Digital SLR, switching an ISO is easy, and could be done at any time. This is a huge benefit, and reduces a need for the faster lenses. Unless you are planning to make money with your camera gear, fastest lenses will not be cost effective.
Consider borrowing, or renting a fast lens, in the range which will meet your shooting needs, and test it in the different environments in which you will be shooting. If you are not pushing the limits of the lens, chances are, you will be OK with a slower, more budget friendly alternative. Make sure that you know your budget, and how actively you will be involved in photography. If you plan to trade-up your equipment in a few years, keep in mind that technology only gets better, and making a big investment will make more sense if you are going to get a lot of use out of it.
By: Sam Zaydel
About the Author:
Written by Sam Zaydel, Professional Photographer, and part owner of a Black and White All-Digital Photography Lab. Our Lab specializes in custom conversions of digital color to Black and White images. We are a custom service, and approach all image conversions individually to offer best possible results. No automated process comes close to the quality of Black and White conversions we produce. To learn more about how you may benefit from our service, please consider visiting our Digital Black and White Photography Lab.
