Now that you have a new camera and know the basic exposure controls, it is time to get serious about selection of lenses for nature photography. First, understand that brand is not as important as quality and functionality. Generally, it is best to stick to lenses made specifically for your camera body - usually by the camera manufacturer, but not always. Most photographers will tell you that the quality of your glass is more important than the quality of your camera. So what questions must be asked to select the lenses that will help your improve you images the most?
Before you can choose a lens you must consider if you want a lens that will work only for your current camera body or will it work or future camera body upgrades. Most companies make a line of lenses that is designed specifically for smaller, crop sensor cameras. These sensors are smaller than full-frame sensors that are the size of 35mm film (actually about 24x36mm.) All entry-level digital single lens reflex cameras currently use a crop sensor. The crop factor is typically 1.5 on Nikon and 1.6 on Canon cameras (more about crop factor later.) Lenses made especially for the crop-sensor cameras (Canon calls these EF-S lenses) are usually smaller, lighter, and less expensive so they are aimed at the entry-level photographer. While they work well on the smaller cameras (and some are of very high quality), they will not work at all (or even fit on) the high level, full-frame cameras. Other lenses are inter-changeable between crop and full-frame cameras. Canon calls these all around, full-line lenses their EF series. Across the board, the EF lenses are generally of higher quality. Canon also has a special series of EF lenses that are called the L lenses (luxury?) that are identified by a red band around the lens. These are extremely high quality, metal framed lenses, that have improved designs, high quality and exotic glass, and additional weather sealing for professional performance.
The first question in selecting a lens is, what are you going to photograph? If you are shooting exclusively landscapes, your lens selection will be far different than if you are going to shoot birds. Keeping this first question in mind, lets look at some basic issues we all must face when selecting a new lens.
Everything in photography is a trade-off and lenses are no exception. Quality of construction and, most importantly, quality of the glass used is of fundamental importance. There is a huge trade-off because high quality almost always means high cost. Two quality factors easily examined are the exterior construction (plastic versus coated metal) and the lens-to-camera connection (should always be metal, and ideally weather-sealed.) Other factors that must be considered are addressed in the specifications for the lens. Ideally, you want a lens with fast auto-focus and, for longer lenses, image stabilization (or vibration reduction for Nikon lenses.) These features will improve your ability to get well-focused shots with no blur caused by camera shake but also add to the cost of the lens.
The most important feature of all lenses is their "speed" defined by the largest aperture or f-stop. Fast lenses are necessary to freeze motion, shoot in low light, and control the depth of field (DoF.) Fast lenses have a maximum aperture of f/4, f/2.8, or even larger. Since the f-stop is calculated as the quotient between the focal length and maximum diameter of the light path through the lens, it is easy to see that fast lenses (large maximum aperture) are very large lenses, heavy lenses, and expensive lenses. For example, a Canon 400mm L-series f/5.6 lens weighs about 2.75 pounds and costs about $1,300 while its big brother 400mm L-series f/2.8 weighs about 8.5 pounds and costs about $11,500. Maximum aperture is a very big deal!
Another issue to consider is choosing a prime lens versus a zoom. Prime lenses have a fixed focal length and are generally sharper, lighter, and simpler in design. They also tend to be much more expensive because of the quality of construction. Zoom lenses are generally more popular, more complex, and not as sharp. Zoom lenses are also much more convenient for most photographers since they can carry fewer lenses and still frame their shot conveniently from one position. Popularity of zoom lenses makes them sell better and in spite of their more complex design, they tend to be less expensive than their prime counterparts.
Now we come full circle to the first question about photographic subjects and focal length of the lens. The focal length determines the field of view and therefore the 'magnification' of the image. A 'normal' lens gives the approximate view we see with our unaided eyes. The focal length of a normal lens on a full-frame camera is about 50mm (or slightly less.) Lenses with a broader angle of view are called wide-angle lenses and those with a narrower view are called narrow-angle lenses - not really(!), they are called telephoto lenses. Wide-angle lenses are great for landscapes and some close-up work and give the feel that the viewer is immersed in the image. They tend to have great DoF and very close minimal focusing distance. They cause some distortion of the image at close range and are very forgiving in focusing. On the other hand, telephoto lenses are great for wildlife shots and some distance shots. They tend to have a narrower DoF and flatten the perspective of the image thereby removing the viewer from the subject. They tend to cause less distortion and are very sharp but are more critical in their range of focus and minimal focusing distance.
Some zoom lenses cross the line between wide-angle and telephoto. This is very convenient because fewer lenses are needed for a wider range of images but extreme zoom lenses, for technical reasons, tend to be of lower quality and have issues with sharpness and distortion.
In the next posting we will take on the issue of crop factor and its effects on the image and general care and protection of your lenses.