So you bought yourself a SLR camera. What now? You obviously need more lenses.
To find out which lenses to suit your specific use is not always easy. There are several abbreviations and specifications you need to find out, and things are not better by the fact that different manufacturers use completely different abbreviations for exactly the same properties.
Below I take a review of the important features you can find on a lens, and how the different manufacturers label them.
Please note that some specs may be slightly simplified to make the article shorter and more readable. For example, the EC designation marked on Canon lenses indicates that it has an autofocus (Electronic Focus), but also indicates which frame the lens uses.
Aperture
Maximum aperture is something which is stated on all lenses. It tells you how much light the lens can get through to the sensor at its best. Much light means you can keep shooting in darker conditions without the image blurring due to camera shake. Aperture is provided as an aperture number, such as f2.8 (or sometimes 1:2.8). The smaller aperture number, the more light to the camera. Theoretically, the absolute best aperture you can get an objective equal to 1, but in practice the brightest lenses offer a maximum aperture of around 1.2. As usual, the consumer will be satisfied with an aperture number of between 2.4 and 3.2. The higher the aperture number, the cheaper is the lens. Telephoto Lenses often have larger aperture numbers.
On zoom lenses, there will usually be stated 2 aperture numbers (for example, f2.8 - f5.6). The smallest aperture number indicates that the amount of light you get the wide angle, while the largest say how much light you get through to the maximum telephoto.
Focal Length
The first thing to consider when choosing your new lens is the focal length you want. The focal length is given in millimeters, and specifies whether the lens is a wide angle or telephoto. Both have their advantages and disadvantages. With a telephoto you'll naturally get closer to subjects far away. Telephoto lenses are also preferred for portraiture as it protects the facial proportions better than a wide angle, and it is much easier to get a blurred background since telephoto lenses have less depth of field than wide angle. Telephoto lenses have usually also lower brightness than the wide-angle, and are more vulnerable to blurriness during the shoot if there is some camera shake. Telephoto lenses are usually physically larger than the wide angle.
Wide-angle on the other hand is fine for nature photography when you can capture more of the landscape. They're usually good both in brightness and depth of field, and are usually physically smaller and lighter than telephoto lenses. On the negative side the wide angle is not ideal for photographing people, at least not in a pure portrait context. A wide angle gives an impression of greater distance between what is close and what is distant, and it can thus quickly look like that model has a bigger nose and sunken eyes more than she / he really has. There are also more likely to get the so-called distortion with a wide angle, i.e., the straight lines begin to bend into the edges of the image.
The cross between a wide angle and a telephoto is called a normal lens. This is a lens that renders the environment as we see with our own eyes (in relation to distance and magnification). In the 135 format, a normal lens is 50 mm. Everything with a smaller focal length is called a wide angle, while larger focal lengths are called telephoto.
On regular compact cameras with 3x zoom, the focal length is usually extend from 35 mm to 105 mm (according to the 135 format). It is important to remember that the focal length is connected with the size of the image sensor to use it with, allowing the focal length of a lens to change depending on which camera it is used on. To avoid too much confusion, it is common to explain the focal length of that which is equivalent to the 135 format, or the so-called full-frame Digital SLR cameras.
Fixed or Zoom
For most, the most appropriate would be a zoom lens. Then you get several focal lengths in the same lens and therefore let you get away with fewer lenses to meet your needs. Zoom lenses have always two focal lengths specified, for example 18-55 mm, which shows how much zoom range the lens has. If you want this translated into compact camera language, you can just divider the largest number by the smallest, which in the 18-55 mm case gives a zoom of about 3x.
A fixed lens on the other hand, has some advantages. They are smaller and lighter, and usually have better brightness than zoom lenses. It is also easier to correct for various lens error on a fixed lens than a zoom, and thus it is more likely to improve image quality on a fixed lens than a zoom (although this will vary somewhat based on price and producer).
Some consider it more artistically correct to use a fixed lens, and that it is a bit like cheating to use the zoom, but strictly speaking we do not have to worry about it.
Crop Factor
The various camera manufacturers often use different sizes of image sensors in their SLR cameras. This can be confusing in relation to the size of tele or wide angle a lens actually has. The most common trick is to convert the focal length of what it would have been on the 135 format, or the full frame. To make the conversion you need the crop factor. For example, on Canon's SLR cameras without a full frame sensor, the crop factor is 1.6. This means that you must multiply the focal length with 1.6 to determine what it would have been on the 135 format. 18-55 mm will be approximately equal to 29-88 mm.
Nikon - 1,5
Canon - 1,6
Pentax - 1,5
Sony - 1,5
Image Stabilization
Although you'll find optical image stabilization in more and more SLR camera bodies, major manufacturers continue to swear to stabilization in the lens. This is done by moving the lens elements in the lens, which gets the projected image to move the image sensor and thus eliminating camera shake. Manufacturers such as Olympus, Pentax and Sony all use image stabilization in the camera body, so you will not find lenses with stabilization from these suppliers. Below you can see the abbreviations other manufacturers use to specify that their lenses have built-in image stabilization.
Nikon - VR
Canon - IS
Pentax - Image stabilization in the cameras
Sony - Image stabilization in the cameras
Sigma - OS
Tamron - VC
Color Refractive Correction
Photography focuses entirely on the light, and the headache for lens makers is that the light has some strange abilities. One of these is that the different colors of light does bend differently when they pass a lens. This can lead to color shifts, particularly towards the edges in an image. To counteract this, manufacturers are using what they call a low dispersion glass.
Nikon - ED
Pentax - ED
Sigma - APO
Tamron - LD
Distortion
Distortion is a different lens error, where straight lines toward the edges of the image is bent either inward or outward. Most lens manufacturers take this into account during construction and correct it in the best possible way, but it can still occur that you come across specifications, indicating that the lens has correction for exactly this.
Pentax - AL
Sigma - ASP
Tamron - AD
Perspective / Focus Shift
Some lenses for professional use, has the ability to correct perspective. For example, when shooting a high building you may fix the camera slightly upward, and the building will look thinner on top than the bottom. Lens perspective shift can thus rectify this. These lenses also have the option to change the focus plane so that you can improve or worsen the depth of field. As a common consumer it is very unlikely that you'll need some of those lenses.
Nikon - PC
Canon - TS
For Non-Full-Size Image Sensors
After SLR cameras took the step into the digital world, something had to be done with the lenses. First and foremost, because the digital image sensor had a much smaller area than a traditional negative / dias. Since the image surface is smaller the lenses can be made smaller and lighter, but at the same time these lenses cannot be used with traditional film cameras or digital SLRs with a full frame image sensor.
Nikon - DX
Canon - EF-S
Pentax - DA
Sony - DT
Sigma - DC
Tamron - DI-II
For Full-Size Digital Image Sensors
The manufacturers also make lenses for full frame image sensors, of course. These can also be used on regular film SLRs.
Nikon - Lenses are not marked with DX
Canon - EF
Pentax - FA
Sigma - DG
Tamron - DI
Macro
Macro is a feature many will recognize from compact cameras. It is simply the ability to get very close to your subject and be able to take picture of the little things (insects, flowers, etc.).
Nikon - Micro
Canon - Macro
Sigma - Macro
Tamron - Macro
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