If you own a digital SLR, you know there are a lot of lenses on the market, and most of them are definitely outside most people's price range. Purchasing the wrong one can be a costly mistake. While no lens will ever do everything you want it to do for you, you can get yourself a small kit with a few lenses to cover all of the important bases. Where you go from there is up to you and where you want to take yourself as a photographer.
Cover the basics first
Almost all photographers should at least cover the 18mm to 200mm zoom range (what's that? See my article about lens and mm). This is enough of a range to give you most wide-angle and telephoto shots without going overboard on either. Whether you are on the Nikon or Canon system (or any other brand that sells detachable lenses), you should be able to purchase a good 18mm to 55mm and a 55mm to 200mm zoom lens, both with a maximum aperture of F4. These two combined should cost you less than US$400, which is well worth it for covering the basics.
Some people purchase the 18mm to 200mm F4 zoom lens instead of buying both separately. This idea makes sense if you can afford it. Not only is it a pain to change lenses every time you want to make the switch from wide-angle to telephoto and vice versa, changing your lens too often can plague your image sensor with dust and other debris that will have a negative effect on how your photos look.
How to avoid buying more lens than you need
Once you have the basics taken care of, and you still want to get a new lens, take your time and think of a very specific photo you would like to take that you cannot take with your current lens. Advanced macro photography, for example, requires you to use lenses with double magnification to get up close and personal. Only when you have tried several times in vain to get a certain kind of shot with your current setup should you consider upgrading to a lens that might make the photo you envision possible.
Get a lens with a bigger aperture
Some people want to take a lot of indoor photos without having to use a flash. They also want to take photos with such a limited depth of field that it effectively blurs out the background in the shot. If this sounds like you, then you might want to consider getting a lens with a bigger aperture.
The basic lens zoom lens for most digital SLR cameras only gets an aperture as 'big' as F4. With aperture settings, remember that the smaller the number, the wider the aperture and thus the more light you let into the camera. At F4, you can blur out some of the background, but you definitely won't get good low light performance. That's why many people upgrade their F4 zoom lenses. They want the same zoom range with a bigger aperture like F2.8 or F1.4
Unfortunately, it costs a lot more to buy a zoom lens with those aperture numbers. This is because the manufacturers have to make the lens wide throughout the entire zoom range. As soon as you go lower than F4 on zoom lens, you will probably be spending at least US$1000. Nice lens if you can pay for it, but do you really need it?
Probably not, because there are alternatives like a 'prime' lens. A prime lens has a fixed focal length like 18mm, 14mm, etc, and it almost always gives you a bigger aperture range. One of my first prime lenses was a 50mm F1.4 prime lens that I used to take indoor pictures at parties. I couldn't zoom it or anything like that, but it was awesome because I didn't have to use a flash.
Get a lens outside of the ordinary focal range
Depending of what you like to photograph, you might want a lens outside of the basic 18mm to 200mm focal range. Surf photographers often purchase 500mm fixed focal length lenses that get F4, and they're usually good enough to capture the kinds of pictures that make it into surf magazines. You can also go the other way around and purchase a fixed focal length wide-angle lens like a 10mm fisheye. This will help you achieve a unique closeup perspective without spending a ton of money on a zoom.
I highly advise you to take your time when it comes to purchasing new lenses. Start off with the basics and expand your lens collection only to capture new images you can't take with your current lens. Remember, camera salesmen will always try to push a ton of new features on you, but you won't need most of them. Be conservative and enjoy what you have.
If you have a lens you just love to pieces, I want to hear about it. Let me know why you love it, and I might do a feature article on yours (and my) favorite gear.
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