How many lenses do you need for your camera to capture all the beauty of our National Park System? That's a question that can be costly if you're not careful in your selections.

If you own an interchangeable-lens camera (often called an SLR or DSLR) then you have probably been curious about the plethora of lens options that you have. At the very least I am sure you have asked yourself if the lens that came with your camera would be all that you need.

Each lens can be described by two main features: focal length and maximum aperture. We'll talk about each of these presently.

First off, there are two main categories of lenses: zooms and primes. A zoom lens covers a range of focal length while a prime lens has a single focal length. While, historically, prime lenses have been of higher quality than zooms, today's best zoom lenses deliver excellent quality. A lens' focal length is always expressed in millimeters with larger numbers indicating an ability to bring more distant objects closer.

When looking at the focal length of a lens, you must take one camera-specific factor into account: sensor size. Most digital SLR cameras have a sensor that is smaller than a traditional 35mm frame. This makes the camera function as if it had a small magnifier in it which usually means that you have to multiply a lens' focal length by 1.5 or 1.6 to determine how that lens will function on your camera. In general, if you paid less than $2,000 for the camera, then it most likely has this multiplier. If your camera is a Canon then use 1.6x and use 1.5x for most other manufacturers.

Traditionally, 50mm is considered a 'normal' lens (remember to take into account your camera's multiplier) meaning that it is sees the world pretty much as you do; providing no magnification. A 100mm lens provides about 2x magnification and a 400mm lens provides about 8x. With a Canon 1.6x camera that 400mm lens functions like a 640mm lens on a film camera while a 10mm lens functions like a 16mm. This means that you can get closer to wildlife but need wider lenses to get an entire panoramic scene.

Aperture is a measure of the size of the hole (aperture) that light passes through on the lens. For reasons of geometry, the smaller the number the larger the hole, thus more light gets through the lens. A lens with an f/2.8 aperture allows in more light than one with a f/5.6 aperture.

Lenses are rated on their maximum aperture at a given focal length but are capable of using smaller apertures (and usually do). A zoom lens will often have a range listed for aperture such as f/3.5-5.6. This means that at its shortest focal length it is capable of f/3.5 and at its longest focal length it is capable of f/5.6. Some lenses are capable of a constant maximum aperture throughout the zoom range and their aperture is listed as a single number such as f/2.8. Generally, a constant maximum aperture lens costs more than a variable maximum aperture lens.

A 70-300mm f/4.5-5.6 lens is capable of f/4.5 at 70mm and f/5.6 at 300mm with in-between focal lengths providing a maximum aperture between f/4.5 and f/5.6. A 24-105mm f/4.0 lens is capable of f/4.0 at any focal length.

Larger aperture (smaller the number) lenses tend to cost more but deliver better low light performance. They will usually focus better in low light and allow you to shoot without a flash in more environments. The largest aperture generally available on telephoto lenses is f/2.8. The largest aperture available on more affordable lenses is usually f/4.0 or so.

Larger aperture settings also provide more background blur and are used extensively for portraits. There are also some interesting creative uses for large aperture settings, but I'll save that for another time.

Essential lens: the walkaround

Your camera may have come with a perfectly good general-purpose 'walkaround' lens. Most do. For a walkaround lens I recommend a lens with a focal length range from about 20-100mm. 20mm or so is wide enough to capture most landscapes and 100mm can get you a little closer to wildlife. For this lens I consider stabilization a must: either in the lens or your camera body. Since this lens will be on your camera most of the time you will want to make sure it is a good quality lens. You may find that for landscapes you prefer a wider lens and most manufacturers offer lenses that start at about 17 or 18mm wide. Except for the most sweeping panoramas, 17mm should be wide enough.

Wildlife lens

Do not approach wildlife. Get a long lens to keep yourself and wildlife safe.

300mm is a good focal length for relatively close wildlife. Elk on the next hill will still be small but will be recognizable as elk. For better reach, you can usually find a lens that reaches out to 400 or even 500mm. However, to go beyond 300mm usually requires a serious investment. You may find lenses advertised as 500mm/1000mm. These lenses are manual focus lenses with a universal mount and a 2x converter. I don't generally recommend these lenses, but with careful focusing and a good tripod you can get decent results from them. 70-300mm is a very common range for this sort of lens.

You can also add a supplementary lens called a teleconverter that gets placed between the camera and lens. The teleconverter will usually provide 1.4x or 2.0x magnification, thus turning your 70-300mm lens into a 140-600mm lens. The downside to teleconverters is that they can degrade image quality and will reduce the amount of light that reaches your autofocus sensor, something that can cause autofocus problems. That said, a good 1.4x teleconverter might be a worthwhile investment if your longest lens is 300mm.

Macro

Macro lenses tend to have some of the best optics available from a manufacturer. While many telephoto lenses may contain the word 'macro' in their name, they generally fall short of what a true macro lens is capable of. All good macro lenses are capable of attaining 1:1 magnification, which means that an object that is 1" appears on the sensor as 1". Some lenses are even capable of greater than 1:1 magnification. These are very specialized lenses and not something found in most photographer's bags.

I highly recommend getting a macro lens if your bag has room for one. You will see the closeup world differently when you have a macro lens on your camera. You will find details that you never knew were there and, I hope, get more out of your park experience.

Ultrawide

Smaller-than-35mm-frame sensors have necessitated a new category of lens: the ultrawide. As mentioned earlier, these 'crop factor' cameras make long lenses longer, but they also make previous-generation wide angle lenses less wide. Thus the ultrawide. These lenses are great for scenic shots, but often do not provide long enough reach to be most people's general purpose lens. The ultrawide lens usually comes in a range from about 10-20mm. If you are comfortable with assembling multiple shots into a seamless panorama then this may not be an essential lens for you, but if you want a single shot that covers up to about one-half of the vista before you then the ultrawide is what you want. One downside with such wide lenses is that they tend to distort vertical lines near you, making trees appear to be growing at an angle. I used an ultrawide lens in Yosemite for most of a day and was thrilled with the results, although I did have to correct some images to straighten the trees.

The megazoom

Many lens makers have started to make a lens that tries to be the one lens for everybody. These lenses usually come in a range of 17 or 18mm to 200 or even 250mm. The first generation of these lenses did not provide the best image quality and often suffered from poor focusing accuracy and speed. These lenses have been updated and many now feature stabilization (for Canon & Nikon bodies). Reports have been better but I would advise reading reviews and trying the lens beforehand if possible. If the f-stop range of a lens goes beyond 5.6 then you will likely have troubles with autofocus in anything but bright daylight.

Other features

Dust/weather sealing is generally only featured on 'pro' lenses, but after getting caught in a dust storm in Utah I will never travel without weather sealed lenses. While the dust did work its way out of my old lens, it spent a few months with a 'crunchy' feeling zoom ring. Not so with my new, sealed lenses. Even after a photographer's tour of Antelope Canyon with its omnipresent airborne dust my sealed lenses are smooth.

Stabilization is now offered on most new lenses (or in-body, depending on your camera manufacturer). For lenses wider than about 100mm or so you may not find stabilization to be necessary, but on telephoto lenses I consider it a must. You will get a much higher percentage of keepers with a long stabilized lens.

In my bag

My main camera bag always has the following four lenses in (often a few more):

*Canon 100mm f/s.8 macro - Perhaps my all-time favorite lens

* Canon 24-105mm f/4.0L IS USM - My general-purpose walkaround lens. Super-sharp and weather sealed.

* Canon 70-300mm f/4.5-5.6 IS USM - My default telephoto lens. Not as sharp as my 100-400mm lens, but much smaller, lighter and less conspicuous

* Canon 50mm f/1.8 - This lens is very sharp and amazingly affordable. I rarely use it but it is very small and I keep hoping to find it useful

Happy shooting!