Two Stand-Out EF-S Lenses from Canon

If you’re a photographer using a Canon Digital Rebel camera, or one of the prosumer models like the EOS 20D to 50D, you’ll find your wide angle options limited.

This is because of the crop factor that results from using a sensor that’s smaller than 35mm film. These smaller sensors, called APS-C format, are only 22.5 x 15mm in size, whereas a frame of 35mm film is 36 x 24mm in size.

The crop factor in practise is similar to using a longer lens, or 1.6x tele converter, on your Canon digital SLR (unless it’s a full-frame camera like the EOS 1Ds or 5D series).

That’s a distinct advantage when using telephoto lenses as you’re effectively enlarging the image in your viewfinder, adding reach to your lens. So a 200mm lens on your 40D is similar to using a 320mm lens on a full-frame body.

But for wide angle shots, the opposite is true. A relatively wide lens like a 24mm, when fitted to your Rebel XSi, is now like using 38mm lens.

To cater for its customers using EOS digital SLRs with APS-C format sensors, Canon has introduced a range of EF-S lenses designed specifically for use with these cameras.

Most of these lenses, like the EF-S 18-55mm f/3.5-5.6 IS “kit” lens, are reasonably capable, but of flimsy build quality. There are no L-series lenses within the EF-S range.

Fortunately Canon has introduced two EF-S lenses that do stand out from the crowd.

The Canon EF-S 17-55mm f/2.8 IS USM is a standard zoom, with equivalent focal length of approximately 27-88mm. Its stand out feature is the constant f/2.8 maximum aperture throughout the zoom range. This, together with superior image quality, excellent image stabilization and fast auto focus, make it a favorite of portrait and wedding photographers, and any others who need to shoot in low light.

It’s the most expensive of the EF-S lenses and is also big and heavy, but highly rated by users.

The Canon EF-S 10-22mm f/3.5-4.5 USM is remarkable because it’s a true ultra wide lens for Canon Rebel and 20D-50D users. On these cameras its equivalent focal length is 16-35mm, definitely qualifying as ultra wide at the 16mm end.

This lens is also highly rated by users, with some comparing the image quality to that of a Canon L lens, while also praising its sharpness and excellent color rendition.

For those who can afford them, these two EF-S lenses certainly add a new dimension of creative possibilities for photographers using Canon Rebels, any of the EOS 20D to 50D bodies, or the new 7D.

See Canon Lens Reports for more information and user ratings.

Cheetah Picture Using Canon L-Series Lens

This picture of a young cheetah was taken in Botswana, using a Canon EOS 400D (Digital Rebel XTi)) camera plus Canon EF 100-400mm f/4.5-5.6L IS USM telephoto zoom lens at 320mm focal length. The shutter speed was 1/50 and aperture f/5.6, using aperture priority mode.

The Canon EF 100-400mm tele zoom is a useful lens for wildlife and sports photography because of its wide zoom range and image stabilizer. The main drawback of the lens is the fairly slow f/5.6 maximum aperture when used at the longer focal lengths. There has also been some criticism of the pull-push zoom mechanism, but most photographers who use the lens quickly adapt to this and don’t find it a hindrance.

This is one of Canon’s L-series lenses, easily identified by the red ring around the lens barrel. The “L” designation is generally taken to mean “luxury”, as these lenses are aimed at professional photographers who demand superior image and build quality and are prepared to pay premium prices.

To satisfy these demands, L lenses are made with special optical materials, including fluorite elements and UD (ultra-low dispersion) glass. They are also more ruggedly built than normal lenses, with extra weather sealing to keep out dust and moisture. To read a more in-depth article, see Canon L Lenses.

Canon Digital SLR Crop Factor

Canon digital single lens reflex cameras do not all come with the same size digital sensor or chip.

On Canon full-frame digital SLRs such as the Canon 1Ds and 5D models, the sensor is the same size as a film negative - 36mm x 24mm.

On the Canon 1D models, the sensor is slightly smaller, measuring 28.5mm x 19mm (referred to as an APS-H sensor), while on the Canon Digital Rebels and 30D, 40D, and 50Ds, the sensor is even smaller, measuring 22.5mm x 15mm (referred to as an APS-C sensor).

Normally, with lenses designed for 35mm film cameras and digital SLR cameras, the image projected by the lens fully covers the area of the negative or full-frame sensor. However, when you substitute the sensor with one that’s smaller in area, part of the image flows over the edges of this smaller sensor. It’s like showing slides or an old home movie on a screen that’s too small, so the picture “overflows” the screen.

This can be seen in the example below, where the black lines represent a full-frame sensor, the blue lines an APS-H sensor, and the red lines an APS-C sensor:

The practical implications for photographers are far-reaching, as the image received by the smaller sensors is apparently now magnified - it fits on the full-frame sensor, but is too big for the smaller ones. The effect is similar to using a teleconverter - or post-processing by cropping the image in an image editor. This is great for photographers using long lenses, as their teles now have more reach, but it’s not so great if you shoot wide angle, as your wide angle lens is now more like a standard lens.

This effect on the image caused by smaller sensors is known as the “crop factor” or “focal length conversion factor” - for more information, see this article about the Canon Digital SLR Crop Factor.

For general information about Canon lenses, see these articles:
Canon Telephoto Lenses
Canon Zoom Lenses
Canon Wide Angle Lens