What Digital SLR Lens Should I Buy?

If you have recently taken a plunge into the DSLR world and want to get a new lens but not sure which one to choose continue reading. This is a generic guide to various types of lenses and how to choose based on the type of photography. It will take you one step closer towards the right lens for your brand of camera.

Most production consumer lenses are manufactured by Canon, Nikon, Sony, Olympus, Pentax, Panasonic, Sigma, Tamron, Tokina and Zeiss.

Out of these, Sigma, Tamron, Tokina and Zeiss make lenses for different brands while the others only make for their own brands of cameras. One exception is Four Thirds and Micro Four Third formats which are compatible with any brand of the same format of camera.

Once you understand the basics behind choosing the right camera lens for your needs, you can make a short list of focal lengths and apertures and search for them for more research. In the near future we will be making a short list of the best lenses available in the market for each brand of cameras.

While choosing a lens there are 2 major factors to consider.

Focal Length

Focal length of a lens decides how far or how wide can your camera see. The lower the focal length the wider the picture visible to its sensor, the higher the number the further it sees.

Important Note: If you have a DSLR with APS-C sized sensor (23mm) then you need to multiple focal lengths by a factor of 1.6x when using a lens that was originally made for film or full frame (35mm) sensors. This is due to the fact that smaller sensors will cut a portion of the frame from the sides therefore resulting in a narrow field of view.

Here is an interesting article explaining this in full detail.
http://www.bobatkins.com/photography/tutorials/crop_sensor_cameras_and_lenses.html

Many manufacturers now make lenses that are designed for APS-C cameras only. In that case a multiplier of 1.6x is not applicable.

Modern lenses are broadly divided into two separate types. Primes and Zoom Lenses.

Prime Lens

A prime lens has a fixed focal length. It means that you cannot zoom in or out. However since there are fewer glass elements in the construction of the lens, the picture quality is usually much better than an equivalent zoom lens.You should choose a prime lens when you sharpness is of importance or for low light shooting and when you have room to move around to counter the lack of zoom. Prime lenses are generally more compact and lighter than zoom lenses of equal maximum aperture (more on aperture below).

Popular prime lenses come in below focal lengths:

Note: Not all manufacturers make these lenses listed below. It is possible that Prime lenses with some of these focal lengths are not available for your camera model.

Ultra Wide Angle Prime Lens:

Some samples from a 8mm Lens.

8mm Fisheye: This is a ultra-wide angle focal length. Due to the extreme wide angle nature of the lens, the image is distorted in a round fashion.

Some samples from a 14mm Lens.

14mm, 15mm, 20mm: These do not have the fisheye effect but might have slight distortion. All these lenses are great for capturing landscapes or real estate pictures or simply capturing the scene with a dramatic effect.

Wide Angle Prime Lens:

24mm, 28mm, 30mm: On a full frame (35mm) DSLR these will still be considered as wide angle lenses. If same lenses are used on APS-C cameras, then they are not.

Standard Prime Lens:

35mm, 50mm, 85mm: These are great for taking portraits and “normal” shots. These normally come in with the biggest apertures,sometimes up-to f/1.4,which is extremely useful for night time or low light portraits or a blurry background (bokeh) effect.

Telephoto Prime Lens:

100mm, 135mm, 200mm: Ideal for taking portraits from a distance, also for sports or wildlife if not too far and if there is room to move. These lenses also have a large aperture of around f/2.8 therefore great for low light photography.

Super Telephoto Prime Lens:

300mm, 500mm, 600mm or more: When you really want to get close to the subject without being too close, these are the lenses that will help. Due to their large physical size, these are the biggest, heaviest and the most expensive of all lenses. Usually used by professional sports and wildlife photographers.

Zoom Lens

Zoom lenses are more popular than primes because they have a variable focal length therefore can be used in a variety of situations. However due to a larger number of glass elements image quality often suffers in zoom lenses specially if the zoom range is greater. Other side effects of a larger zoom range in a lens include bigger size or smaller apertures or higher costs. Choosing a proper lens is therefore maintaining a balance between zoom range, maximum aperture, image quality and cost.

Here are popular focal length ranges in zoom lenses (might not be available on all brand names)

Ultra Wide Angle Zoom:

10-20mm, 10-22mm, 11-18mm, 16-35mm, 17-35mm: Great for landscape photography. These run upwards of $600 and also have large construction and need a large filter.

Wide Angle Zoom:

17-50, 20-35mm, 18-55mm (these are not too wide on APS-C Sensors) Great for landscape and portraits

Standard Zoom:

28-80mm, 35-70mm, 28-75mm, 28-105mm, 28-135mm : Great for portraits and general purpose photography. These are usually the cheapest zooms due to their low aperture and low build quality.

Telephoto and Super Telephoto Zoom:

70-200mm, 70-300mm, 100-300mm and more: These are generally used for sports, wildlife, astronomy etc. where a longer reach is required.

Aperture

Maximum Aperture in a lens is another major factor to consider while choosing a lens. So what exactly is an aperture of a lens? It is the opening in the lens through which the light goes through. This is normally controlled via a number of shutter blades in a lens. The blades move in and out when the camera sends a signal to the lens and the aperture gets bigger or slower.

Here is a great article on aperture: http://en.wikipedia.org/wiki/Aperture

The bigger the aperture, more the light reaching the sensor therefore making it possible to take pictures in low light conditions. If the lens has a smaller maximum aperture, then less light will be available therefore you will need to compensate it with keeping a slower shutter speed. This in turn might require you to use a tripod to reduce blur or use a Flash or use a higher ISO sensitivity setting.

Now a days DSLRs can make use of very high sensitivity and give very clean pictures up-to say 1600 ISO, therefore allowing a photographer to use lenses with smaller apertures.

Typically in a commercially available lens Maximum apertures range from F/1.8 to F/5.6. You can stop down to F22 on all these lenses. The lower the number the larger the aperture (opening) is. Therefore while choosing a lens it is important to pay attention to the aperture number on the model number.

Some samples from a Large Aperture of F/1.8.

For e.g. a Canon EF 50mm F/1.8 Lens has a maximum aperture for F/1.8 which makes it great for taking portraits in low light (indoors or at night).

A Tamron 17-50mm F/2.8 Lens has an aperture for F/2.8 which is smaller than a F/1.8 but still good enough for low light.

Once you go above F/2.8 it becomes difficult to take pictures in low light unless you have a tripod or use a Flash or use a high ISO sensitivity.

Aperture also controls the depth of field in a picture. A large aperture of say f/2.8 will give a shallow depth of field. Which means more of the picture in front and in back of the subject in focus will be blurred out. If you need the capability to blur the background of a subject and only keep the subject in focus, you need a lens with a large aperture of F/2.8 or larger.

For landscapes a smaller aperture is needed for more depth of field. Normally one would use a aperture of F/16 or F/22

Some samples from a Smaller Aperture of F/16.

How to Interpret a Lens’s Capability Based On It’s Name?

Lenses are named based on their focal length and its Maximum Aperture.

For e.g. a Canon EF 85mm F/1.8 lens has a focal length of 85mm and a max Aperture of F/1.8

Since it’s name only has one focal length and only 1 aperture value it means that it is a Prime lens (no zoom) with a fixed maximum aperture.

Now lets take another lens for an example

Canon17-40mm F/4 Lens: Notice that this lens has 2 values for focal length. 17mm and 50mm, which means that this lens can zoom from 17mm to 40mm therefore going from Ultra Wide angle (on 35mm sensor) to a standard focal length. Therefore you can use it for both landscapes and portraits. Notice it also has only 1 maximum aperture of F/4 which is not so great for low light photography.

Finally lets take this lens

Canon 15-85mm F/3.5-F5.6 IS lens: This lens has an zoom range of 15mm to 85mm which is again great for landscapes and portraits. However, it also has a variable maximum aperture. At 15mm it will have a max aperture of F/3.5 and as you zoom towards 85mm the aperture will come down to F/5.6 (smaller aperture at 85mm) which will result in loss of light at 85mm. This also means that as you zoom in and out the camera will have to re evaluate the exposure settings. The “IS” in the name stands for Image stabilization which means that the lens can compensate for some blur caused by shaky hands. Only up-to a small extent though. Some manufacturers use OS (Optical Stabilization) or VR (Vibration Reduction) or VC (Vibration Compensation) and so on. It is the same concept.

Other Factors To Consider…

Build quality: If a lens is going to be used outdoors a lot then build quality is important. Some high end lenses have a weather sealing (Canon L Series) keeping water and dust out of the lens.
Auto and Manual Focus: Most modern lenses come with both auto and manual focus. However some of them have a switch for manual focus while some high end lenses allow full time manual focus, which means that you can change the focus manually which still on autofocus setting.
Front Filter size: The larger the filter size the more expensive it is.
Rotating front element: If you want to attach a ND Graduating / Polarizing filter to the front, and if the front rotates while focusing, these filters wont give you the results you want.
Focus Speed and Noise: Lowe end lenses have slower focusing and may not be fully silent. Slow speeds are not good for sports and wildlife where speed is important. Noise is not good while taking pictures of bugs or capturing video etc..

Specialty Lenses

Certain types of photography require specialty lenses. The 3 main types of specialty lenses are

Some samples from a Fisheye lens.

Fisheye Lens:

These are great for capturing a very wide area in a single frame. It also gives a dramatic effect to the subject.

Some samples from a Macro Lens.

Macro Lens:

Macro lenses allow you to get real close to the subject such as bugs, jewelry or coins etc..

Macro lenses usually have a magnification of 1:1 (actual size) or 1:2 or even 1:4. Macro lenses usually have large aperture of F/2.8 and are also great for portraits as they produce a sharp image. Also dedicated macro lenses have fixed focal lengths.

Typical macro focal lengths include

50mm, 60mm : Great for product photos, coins, jewels and small lifeless objects.
90mm, 100mm, 105m: Great for flowers, bugs etc. where getting close to wont affect the ability to take pictures.
135mm, 180mm, 200mm: Great for taking macro shots of bugs etc. from a much larger distance.

Tilt Shift Lens OR Perspective Control Lens:

Some samples from a Tilt Shift Lens.

These lenses are usually used to eliminate the convergence of parallel lines while shooting tall buildings. They can also be used for landscapes and portraits.

Here is more on Tilt Shift Lenses http://en.wikipedia.org/wiki/Perspective_control_lens

To summarize :

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