Lenses. Buying a camera lens; advice.

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	Lenses

Lenses

One of the advantages of a 35mm SLR system is that it provides for interchangeable lenses. One camera body is able to accommodate a wide range of lenses, from a 16mm extra wide-angle lens to a 500mm telephoto lens. (As long as your pocketbook can accommodate them, that is!) But what are the differences between lenses? Which ones do you need?

Below are some important features to consider regarding lenses:

Lens Focal Length

One factor that defines a lens is its focal length. The focal length determines the amount of magnification and the angle of view provided by the lens, and is identified by a measurement such as 50mm or 180mm. Lenses are often classified into three groups of focal lengths: wide-angle, normal, and telephoto.

Wide-angle lenses provide the least amount of magnification and the widest angle of view, making distant objects appear relatively small. Some common wide-angle lenses are 20mm, 24mm, 28mm, and 35mm. These lenses are able to provide a relatively large depth-of-field.

The traditional normal lens has a focal length of 50mm.

A telephoto lens has a long focal length. Some common telephoto lengths are 105mm, 200mm, or 300mm. These lenses offer high magnification and a narrow angle of view. This brings distant subjects up close. Due to the high magnification of these lenses they are especially susceptible to camera shake, so it is important to use them with a tripod.

Lens Speed

Another factor that defines a lens is its speed. Lens speed is determined by its maximum aperture. The larger the maximum aperture, the faster the lens is considered. For example, an f/2.8 lens is faster than an f/5.6 lens because the corresponding shutter speed required at f/2.8 will be two stops faster than at f/5.6. Faster lenses are normally more expensive and heavy and be aware that you may not use the largest aperture setting very frequently since the depth-of-field will be so small. There is no direct advantage to using an f/16 aperture on an f/2.8 lens as compared to using an f/16 aperture on an f/5.6 lens. However, since a lens opens up to its maximum aperture when not in use, the viewfinder display on a fast lens will be brighter. This makes composing and focusing a subject a bit easier.

Primary or Zoom Lens

A lens is either a fixed focal length lens, often called a primary lens, or a zoom lens. A primary lens offers one focal length, such as 35mm. Zoom lenses provide a variable focal length, such as 35-70mm. Zoom lenses are becoming exceedingly popular due to their ease of use and the fact that it is normally cheaper to own one zoom lens than multiple primary lenses covering the same range.

Many inexpensive zoom lenses offer a variable aperture. For example, a 70-210mm f/4-f/5.6 lens has a maximum aperture of f/4 at the 70mm setting but a maximum aperture of f/5.6 at the 210mm setting. This effect is also evident at all focal lengths and aperture settings. For example, f/8 may provide the proper exposure at 100mm, but will result in a slight underexposure at 180mm. Always re-meter the subject when changing focal lengths with a variable aperture zoom lens.

Each photographer has different preferences and requirements regarding focal lengths. It may be a good idea to start with one lens in the normal focal length range. This range is dominated by zoom lenses. If you are unsure of your needs, start with one zoom lens, perhaps with a 35-70mm range, and discover what your needs and wishes are after using that for a period of time. Extra wide-angle lenses and strong telephoto lenses are more difficult to use correctly and strong telephoto lenses are typically quite expensive, so be certain of your needs before acquiring those.

Manual Focus or Automatic Focus

A lens is either a manual focus or automatic focus (AF) lens. Automatic focus lenses normally have the option to also be used in manual focus mode. Somewhat surprisingly, manual focus lenses are generally about the same price as automatic focus lenses. If you plan to purchase an AF lens and frequently use it in manual focus mode, be sure its manual focusing ring is adequately sized and easy to use.

Brand of Lens

The brand of lens you need is dependent on the brand of camera you own. Each brand of camera has a different type of lens mount. For example, a Canon lens will not fit on a Nikon camera. You need to buy lenses made by either your camera’s manufacturer or by a third-party lens manufacturer, which typically makes versions of their lenses for all popular camera brands.

Optical Quality

Determining which lens to buy is greatly complicated by the issue of optical quality. For example, you could purchase an inexpensive 28-300mm third-party zoom lens to cover a large range of focal lengths. But how important is optical quality to you? And exactly what level of quality does that 28-300mm lens provide? These are questions that could trigger a long and contentious discussion among photographers.

Lenses with high quality optics typically come with high prices. You should do some research before deciding which lens is best for you and your budget. However, I have found lenses to be the most frustrating type of photographic equipment to research because so much contradictory information exists. It is difficult to objectively evaluate a lens. While you should normally stay away from poor lenses, a great photograph can easily be produced with an adequate, inexpensive lens. An expensive lens is useless without proper technique. The optical difference between a high quality lens and an adequate lens is often relatively small, important primarily to someone with especially demanding requirements. For example, if you want to produce an 11"x14" print from any type of photograph taken at any aperture setting with amazing clarity, you likely will need an expensive lens. I don’t mean to dismiss the importance of high quality lenses, but if you are just starting I would not get too caught up in acquiring the absolute best lenses. Proceed cautiously and slowly. Add to your lens collection only when you have a specific need for a certain lens and only after doing enough research to be reasonably confident about the quality it will provide. It is too easy to develop a mindset that you need the most expensive lenses to take great photographs.

Filter Size

Another factor to consider is the filter size of the lens. If you acquire three lenses with different filter sizes of 52mm, 58mm, and 62mm, you will either need different filters for each lens or some type of adapter. This will add to the overall expense and the amount of equipment you need to carry and maintain.

Close Focusing Distance

The close focusing distance refers to the minimum distance from the lens that a subject must be to be brought into focus. For example, with a 24mm primary lens you may be able to focus on a subject one foot (0.3 meters) away. With a 24-200 zoom lens the close focusing distance may be three feet (0.9 meters) away. Look at the lens specifications to determine this.

Miscellaneous Factors

Other important factors to consider include:

weight of the lens; heavier lenses require a sturdier camera and tripod

length of the lens

durability of the lens

the markings on the lens (for aperture settings, focus distance, etc.)

the size and ease of use of the manual focusing ring and aperture ring; some automatic lenses provide poor focusing and aperture rings

whether the front element rotates when focusing or zooming the lens, which will affect the use of some filters (especially a polarizing filter)

zoom lenses either rotate or push/pull when adjusting the focal length; either is fine but you may have a preference

Subject: Waterfall in autumn

Lens: Nikkor 35-70mm (set at 35mm)
Aperture: f/16
Shutter Speed: 1/2 second
Film: Kodak Ektachrome 100 VS