Importance of Lenses

Lenses are extremely important and play a huge rule in photography. They attribute to as much as 80% of the quality of an image. Lenses are often referred to as "glass".  

Lenses are high-precision instruments. Choosing the right lens for the right type of composition is useful if not necessary. Lenses exhibit certain key characteristics. Learning those characteristics can help choose the right lens for the right job.

Lens Characteristics

• Focal Length. Lenses are marked with a single or a range of focal lengths. Focal lengths typically range from 16 through 200 (but can be lower or higher)
• Aperture. Lenses are marked with an f-stop range typically from f/2.8 through f/22 (but can be lower or higher)
• Stabilization. Lenses may or may not have image stabilization built into them. 
• Diameter. Lenses have a physical diameter. This has nothing to do with the focal length or aperture. It is typically useful only when you have to buy lens accessories such as lens caps, lens hoods or filters. 
• Size. Lenses vary greatly in size from a few inches to over a foot or more. 
• Weight. Lenses can have varying weights from light to extremely heavy. Very good lenses tend to be very heavy and very expensive (though exceptions exist). 
• Focus Distance. The distance from your camera sensor that objects must be in order for the lens to see them. 
• Focusing Speed. Good quality lenses can focus faster. Specially important in low-light situations. 
• "Fastness". Bit of a misnomer but people refer to lenses as "fast" if they support low apertures (less than f/4) because you can use them with higher shutter speeds. 
• Weather Sealing. Lenses may or may not be sealed for weather. Sealed lenses can generally be used in light rain. 

Types of Lenses

• Normal Lens: A lens that has a focal length roughly equal to the diagonal length of the sensor. So, on a full frame sensor that is 50mm. On a cropped sensor that is about 32mm or 35mm which is a standard size.
• Wide Angle Lens: A lens that has a focal length less than a normal lens or < 35 mm. 
• Telephoto Lens: Focal Length >35 mm.
• Zoom Lens. Allows multiple focal lengths on same lens. Zoom 
• Prime Lens. Only one fixed focal length

Lens Selection

• Telephoto lenses
  • Telephoto lenses flattens or reduces distances
  • They can have very shallow DOF (depth-of-field) and can create pleasing 'bokeh' effect
  • Good for taking Portraits
  • Work best in brighter light or with a flash
  • They are good for enlarging far-off objects
• Wide-angle
  • Great for landscape and architecture shots
  • Useful in cramped spaces
  • Not good for portraits, avoid using for that
  • Good for low-light situations
• Zoom Lenses
  • Allows more composition options on a single lens
  • They are great as a general 'walk around lens'
  • They comprise of multiple glass elements
  • Quality is a generally a bit compromised
  • Generally heavy and costly
• Prime Lenses
  • Generally very "fast" so support wide apertures such as 1.2f, 1.4f and 2f
  • They typically have a single lens element optimized for a single focal length
  • They offer great quality in small sizes and lower weights and lower prices
• Macro Lenses
  • A lens that produces an image on the sensor that is 1-to-1 to the object you are shooting
  • Designed to focus within 6 -7 inches from your camera sensor
  • They are great for flowers, insects and for conceptual shots and small objects

What makes lenses expensive?

Lenses are expensive and with lenses price and quality are directly proportional. Here are some factors that make lenses expensive. 

• Inherent glass quality. Clearer the glass, the less it distorts the light - the harder it is to make and hence the more expensive it is
• Aperture or how fast a lens is. Lenses opening wider (smaller f stops) will generally be better and more expensive
• Constant Aperture (generally zooms with multiple focal lengths will offer maximum apertures that are different for the range. 18-55, 3.5-4.5f: meaning at 18mm you can set the f stop max to 3.5 and at 55mm you can set the f stop to 4.5 max)
• Zoom range. The more zoom range you have the more expensive lenses will tend to be. 

Lens buying tips

• The one you got with your DSLR is probably not great
• Get a 50mm prime lens. It is probably the best tool to learn photography and experiment with
• Get a good zoom lens with IS (image stabilization) as your walk around lens specially for travel
• Read lens reviews on Amazon and other websites - great lenses are not hard to find.