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Introduction to Lenses  
One of the biggest appeals of a DSLR is the ability to interchange the lens to one that fits your needs. With so many lenses available, how do you know which lenses are the right ones for you? Here’s a simple guide to understanding lenses!
Focal length
Lenes are always described in terms of their focal length, in units of millimeters (mm). There are many kinds of lenses in the market, but they can be generally grouped by their focal lengths. The focal length of a lens determines the angle of coverage – the smaller the number, the wider the coverage.
Maximum Aperture
The maximum aperture of a lens indicates how much light is transmitted when the aperture is open fully. A lens with a max aperture of f/1.4 allows 2-stops (or double the amount) of light through than a lens with a max aperture of f/2.8 lens. Lenses with max. aperture of f/1.4 or larger are highly prized by photojournalists who seek them out for low-light photography without resorting to flash. The minimal depth of field also endear such lenses to artists and portrait photographers.

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Ultra-wide angle lenses (10mm to 22mm)
Ultra-wide angle lenses cover a very wide area with its focal length, and they are great for taking photos in tight environment (ever tried taking a group photo in a small restaurant?) Ultra-wide angle lenses are also popular amongst landscape photographers who love the sweeping look it provide for landscapes.

While it seems tempting to buy the widest lens possible (yes I made that mistake as a rookie too), ultra-wide angle lenses are
not the easiest lenses to use. They cover a huge expense of area, so you must be cautious about the contents within the picture, or you might just include undesirable elements (such as your feet perhaps!). Ultra-wide photos are also difficult to compose, because you have to pay attention to the vast amount of foreground as well (and include in something interesting).

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Short telephoto lenses (85mm to 135mm)
Wide-angle lenses cover a wide area with less distortion than ultra-wide angle lenses. Until recently, 24mm is considered to be a very wide-angle lens. Photojournalists love wide-angle lenses for their coverage as well as depth-of-field, especially for environmental portraits where you need to show both the subject and the environment.

When using a wide-angle lens, watch out for placing subjects too close to the edge of the photo, as the distortion at the edges are usually unflattering to the subjects!

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Normal lenses (50mm)
If you’d bought a camera in the 60s or 70s, it’d most probably have shipped with a 50mm lens. The 50mm lens provide a natural-looking perspective to the scene, closely approximating what the eye sees, and that is why it has been called the “normal lens”. A 50mm lens is usually very sharp as well, with its simple construction that has been perfected over the decades.
A normal lens also has the advantage in the maximum aperture; most normal lenses have a maximum aperture of f/1.8 at least, which is one to two stops brighter than other lenses. This means that you’re getting two to three times more light going into the lens, which makes the normal lens a popular choice for shooting in available light!

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Wide-angle lenses (24mm to 35mm)
Short telephoto lenses lend a flattering perspective to portraits by slightly compressing the facial features so everything looks more proportionate. Lenses with focal length from 85mm to 135mm are popular as “portrait lenses”, photographers who want something slightly longer to accompany their wide-angle lenses. The maximum aperture for short telephoto lenses is also quite bright, ranging from f/1.8 to f/2, which makes them ideal for throwing the background out of focus to garner attention on the subject instead.

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Telephoto lenses (180mm to 300mm)
Telephoto lenses help magnify distant action, and they’re popular with photographers shooting sports or action, or photographers who just want to capture moments at a distance. Telephoto lenses require good holding techniques to prevent blur, as unsteady handholding movements are also magnified along with the one to two stops brighter than other lenses. This means that you’re getting two to three times more light going into the lens, which makes the normal lens a popular choice for shooting in available light!

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Super telephoto lenses (400mm to 1200mm)
For some subjects such as sports or wildlife, it is impossible to approach them from a close distance. Photographers will select a super telephoto lens to deal with such scenarios, shooting from a safe or permissible vantage point. If you see sports or wildlife photographers shooting with huge long lenses, those are the super telephoto lenses.

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Specialty lenses – Macro lenses
Macro lenses are lenses which focus very close to achieve a highly magnified view of the subject. While lenses usually focus down to 80cm or 50cm (depending on the focal length of the lens), macro lenses can focus to very close distances such as 20cm, giving you the ability to go in close and fill the viewfinder with the subject. Macro photography is a very interesting field of photography, and serious macro photographers will usually invest in a macro lens. They are substantially more expensive compared to a non-macro lens of a similar focal length, and they come in focal lengths of 50mm, 100mm or 200mm.

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Specialty lenses – Tilt & Shift lenses
Tilt and shift lenses are really specialized tools used for very specific purposes. Basically these lenses have built-in capability to tilt the front of the lens to control the plane of focus, as well as shift capability to control the framing within the image circle.

Sounds confusing? Don’t worry – all you need to know that professional photographers use these expensive tilt-and-shift lenses for architecture photography (to keep the buildings looking
parallel and upright) and product photography (to ensure good depth-of-field without stopping down too extensively). Some photographers use the tilt capability to restrict the focal plane for creative images like the one shown here.

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Zoom versus prime lenses
Prime lenses are lenses with only one focal length, while zoom lengths allow you to change the focal length within a range. Prime lenses usually offer a larger aperture due to their simpler designs that allows more light through (which makes them great for low-light photography). Prime lenses also contain much less glass, and they are much more compact and lighter than zoom lenses.
Zoom lenses offer the convenience of having multiple focal lengths in one lens, and you do not have to keep changing lenses to get different focal lengths. But the price to pay is a significantly larger size and heavier weight than a prime lens.

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Image Stabilizers
Image stabilizers are small gyroscopes within the lens that counter the swaying movements of handholding, and let you shoot with lower shutter speeds and yet get sharp images. They’re a technological marvel in photography, and will really save your bacon when you need to nail that shot. Known as Image Stabilizer (IS) in Canon lenses and Vibration Reduction (VR) in Nikon lenses, they perform the same magic in giving you sharp images where you normally wouldn’t be able to handhold steadily. However, image stabilizers will not help freeze subject movements in low shutter speeds.

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Lens description
If you look at your lens, there’s a string of alphanumeric description that tells you all about your lens specifications. Here’s how you can understand the description:

28-135mm f/3.5-5.6

This is a description for a zoom lens. It means that the widest end of the lens covers 28mm, and the longest range of the zoom ends at 135mm. As you zoom from 28mm to 135mm, there is light loss occurring. So the maximum aperture at 28mm is f/3.5 and the max aperture at 135mm is f/5.6. That’s all to it!