How to Evaluate a Digital Camera Lens
When purchasing a digital camera lens there are three questions that have to be answered:
1. What brand of camera is it for?
2. What are you taking pictures of?
3. When will the lens be used?
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Instructions
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1
Find out what brand of camera you have. Lenses for brand X cameras will not work with brand Y cameras without adapters, and using adapters often seriously hinders lens abilities.
Whether buying brand name lenses such as Canon or third-party lenses from manufacturers such as Sigma or Tamron, make sure that whatever lens brand you're considering, it says clearly that it's for your brand of camera.
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2
Determine what kind of pictures you will want to take. Taking pictures of landscapes or sports requires different lenses. The keyword here is focal length. Focal length represents how much magnification your photo will have. If you'd like to see for yourself, visit the Canon focal length demonstrator, under the resources area.
A "wide-angle" lens typically will have a focal length of 40mm or less. These lenses are for scenic views or architecture, but lousy for wildlife or sports.
A "telephoto" lens will have a focal length of 120mm and up. Telephotos are great for getting close to the action, but are not very effective for family portraits or landscapes.
For those not needing professional results, there are versatile lenses that can go between wide-angle and zoom. As an example, see the Nikon lens in the resources area.
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3
Figure out when the lens will be be used. Taking pictures in low light requires lenses with a wide aperture, which is measured in "f/stop." For low light, look for an f/stop of 2.8 or lower. Think of the aperture as a hole that allows light into the camera. The bigger the hole, the more light gets in. When shooting in low light, you need a bigger hole or your photos come out blurry or dark.
The important thing to remember is that the SMALLER the aperture number, the LARGER the hole. So f/2 (1/2) actually is larger than f/4 (1/4). Just remember: smaller number, bigger hole, more light.
Look at the Sigma lens under resources and look for the aperture: f/2.8. (Notice that it also states "for Canon.")
The downside to a large aperture is that a larger hole requires more lens glass, which increases costs.
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Tips & Warnings
When looking for a wide-angle lens be careful not to mistakenly purchase a "fish-eye," which achieves an extreme wide-angle by producing a distorted image. These lenses require a higher level of skill to operate.
A "zoom" lens does not indicate a high level of magnification. A zoom lens has the ability to adjust the focal length. A 16-35mm lens is a wide-angle zoom lens.
