Many people get a new Canon DSLR and find the images lacking something. Since these units can accept different lenses, the question becomes what is the best lens to buy. The answer, unfortunately, is not as simple as the question. It really depends on what types of photos you intend to take.

Walk Around Shooting
Many people want a general purpose lens that will take good pictures in all conditions. This is known as a walk around unit. These units should be fairly light and optically quite good. It is the owner's decision whether to go with a zoom or fixed focal length. The zoom choices should cover the range from about 17mm and up. A fixed focal length should be in the 30mm to 50mm range.

Zoom Advantages
Allows a range of magnification selections
Reduces the need to switch lenses
Commonly found in the used market

Zoom Disadvantages
Typically heavier than fixed focal length devices
Aperture may change at different focal lengths
Could be expensive, especially for fast optics

Fixed Focal Length Advantages
Optical distortion is typically minimal
Lighter construction
Inexpensive units available

Fixed Focal Length Disadvantages
Cannot magnify images in the field
Photographer may need to move around to capture better shots

LandscapeCredit: javrsmith

Walk Around Model

Canon EF 28-135mm f/3.5-5.6 IS USM Standard Zoom Lens for Canon SLR Cameras
Amazon Price: $479.00 $321.40 Buy Now
(price as of Jul 5, 2015)
This unit is good for most uses. Available at a reasonable price. Very popular with owners. Note that it results in a narrower field of view for cropped cameras such as the Canon T5i.

Macro Photography

MacroCredit: javrsmith

If you intend to take photographs of very small items, or detail shots of things like coins, you should consider a macro lens. These specialized devices allow you to get very close to an object. The entire field can be well focused. Various focal lengths are available which let you choose your particular zoom level. Zoom types of macro lenses are also available. Some units, like the Canon 100mm macro, are capable of shooting portraits as well. This increases the versatility of these devices.

Macro Unit

Canon EF 50mm f/2.5 Compact Macro Lens
Amazon Price: $299.00 Too low to display Buy Now
(price as of Jul 5, 2015)
Very popular device at a reasonable price.

Landscape Photography

LandscapeCredit: javrsmith

For landscape photography, the choice is between wide angle fixed lenses, or zooms that include a wide angle at the lower end. If this type of imaging is your primary goal, you can opt for a device that provides a lower range, say 10mm to 20mm. Again, there are advantages and disadvantages to zoom and fixed lenses.

Landscape Zoom Advantages
Photographer can magnify the image to highlight specific details
Various focal lengths are available in popular sizes
Fairly common in the used market

Landscape Zoom Disadvantages
Heavier construction, typically
Expensive, especially for fast optics
Slow optics limit use of these devices inside homes

Landscape Fixed Focal Length Advantages
Lighter weight units
Better optical performance, typically
Cost can be lower

Landscape Fixed Focal Length Disadvantages
Inability to magnify image
Photographer may need to move the camera to get better images
Less common in the used market

Landscape Lens

Canon EF 17-40mm f/4L USM Ultra Wide Angle Zoom Lens for Canon SLR Cameras
Amazon Price: $799.00 Too low to display Buy Now
(price as of Jul 5, 2015)
Very popular unit. Note that cropped sensor owners, (Canon T5i), have additional choices that are wider.

Portrait Photography

If portraits are the intended use, fast optics are much better. Choose one with a focal ratio as low as possible, perhaps f2.8 or lower. While many of these units can be expensive, for faster optics, there are less expensive choices as well. The famous Canon Nifty Fifty is a 50mm fixed unit at f1.8. It allows many creative effects to be captured in portraits. Chiefly, this device produces good brokeh. This is the term for portraits that highlight the subject with good focus while blurring the background. The overall effect is to draw attention to the main subject, minimizing the impact of the background.

Portrait Zoom Advantages
Zoom lenses can take images of landscapes or portraits
Some have macro capability allowing close focus on small items
Common units
Available in the used market

Portrait Zoom Disadvantages
Better optics can be expensive
Heavier devices
Some may produce sharper images at certain focal lengths, worse at others

Portrait Fixed Focal Length Advantages
Lighter unit
Good, fast optics are less expensive
Some models have macro capability

Portrait Fixed Focal Length Disadvantages
May be scarce in the used market
Less flexible due to lack of magnification

Nifty Fifty

Canon EF 50mm f/1.8 II Camera Lens
Amazon Price: $125.00 $110.00 Buy Now
(price as of Jul 5, 2015)
Practically a must buy for virtually every Canon owner.

Cropped Sensors

Certain Canon models, like the EOS Rebel T5i, are built with a smaller photographic sensor. Full frame units, like the Canon 5D, have a larger sensor which is comparable to the classic 35mm film size. Cropped sensors have the effect of magnifying the focal length by a factor of 1.6 times. That means that 10mm lenses are actually 16mm on a T5i. Similarly, a 50mm unit acts like an 80mm unit. This is a design feature that cannot be changed. It results in a narrower field of view, or higher magnification. As such, images are less wide than they would be otherwise.

Adjusting to Cropped Sensors
Great photos are taken with cropped sensor cameras all the time. The key is to shoot images with the proper balance of gear and conditions. When purchasing a lens, keep the crop factor in mind. If a wide angle is desired for landscape photography, consider buying a unit that is wider. Those with 10mm focal lengths produce a very wide image, even on a Canon T5i. At this focal length, distortion is usually minimized.

Notice that many ultra wide angle units may be available as "fisheye" models. This type will provide the widest shots but with a great deal of distortion at the edges. Photographers then have to choose to accept the distortion, crop out the middle portion of the image, or use software to lessen the distortion.

Nighttime Photography

Shooting at night is possible with virtually any type of gear. Obviously there is a lack of available light. Faster optics may be advisable. Alternatively, using a tripod will allow longer exposures to capture more light. A remote shutter release is highly advised for all tripod photography. This device allows the shot to be taken without disturbing the camera. The result is an image which is in better focus. Notice that images of stars may not produce great results without even more specialized gear. As the Earth rotates, stars appear to move. This will impact your image by producing trails of light, or less focused stars, during longer exposures. To counter the apparent movement of the stars, tracking gear, such as that used with telescopes, is necessary. Alternatively, a telescope adapter will allow the camera to take better star images.