Which big lenses/small sensor digital SLR to buy?

by Philip Greenspun; revised April 2007

Canon is the strongest competitor in the digital SLR market. Their current (2006) big lenses/small sensor options include the following cameras:

• Canon Digital Rebel XTi, $520 (review); 485g; called "Canon EOS 400D" outside the U.S.; introduced fall 2006
• Canon EOS 30D, $760 (review); 700g; introduced May 2006

These bodies are very similar in performance with sensors that are about the same size and 8-megapixels in resolution. The 30D offers better performance in low light, more responsive operation, and a rear control wheel that makes for faster operation in manual or limited-automation modes. The Digital Rebel is lighter and less bulky.

If you have a substantial investment in Nikon-mount lenses you might wish to stick with the Nikon system when buying a digital SLR. At many points in time Canon makes slightly more advanced bodies, but in virtually every photographic situation you'd end up taking the same picture with either the Canon or Nikon big lenses/small sensor body. Nikon's current (2007) options include the following:

• Nikon D40, 18-55mm kit, $429 (review)
• Nikon D80, $1000 (review); 600g; introduced fall 2006 but based on the D70, which was introduced in early 2004
• Nikon D200, $1289 (review); introduced in March 2006
• Nikon D2Xs, $4300 (review); 1070g; introduced early 2005;

All of Nikon's digital SLR cameras use the same size 16x24mm sensor, which multiplies lens magnification by 1.5. The D2Xs is the heavy professional 12-megapixel model. The D200 is the advanced amateur 10-megapixel model. The D80 is the mid-range 10-megapixel model, much lighter in weight due to its plastic body. The D40 is a delightful light compact 6 MP camera with an intuitive user interface. The D40 is the only SLR camera that shows example photos to illustrate the appropriate use of different settings.

Before you consider buying anything other than Canon or Nikon, remember that a 300/2.8 telephoto lens, the standard tool of sports and wildlife photographers, will cost around $4500 to buy and $50 to rent for a weekend. You can rent lenses for Canon and Nikon, or a backup body, in any larger city.

Get a body and normal lens

Lenses are specified by focal length in millimeters and aperture, a ratio between the diameter of the lens and its length. The longer the lens, the greater the magnification. A 50mm lens gives approximately the same perspective as normal human vision. A 400mm lens gives a view like looking through 8X binoculars and a 20mm lens is a dramatically wide angle lens. Lens apertures or f-stops have the following full steps: 1.4, 2.0, 2.8, 4, 5.6, 8, 11, 16, 22. Each step represents half as much light being admitted to the sensor. "50/1.4" is shorthand for a lens that is 50mm long and has a maximum aperture of f/1.4. Zoom lenses are specified with the focal length range followed by the aperture range, e.g., "24-105/2.8-4" is a lens that goes from a wide 24mm perspective to a telephoto 105mm perspective while the maximum aperture available goes from f/2.8 at the 24mm end to f/4.0 at the 105mm end. A "fast" lens is one with a wide maximum aperture, e.g., f/2.0. A "slow" lens is one with a physically small (though numerically large) maximum aperture, e.g., f/5.6. The slow lens will require a more brightly lit scene in order to deliver adequate illumination to the sensor.

You've bought, or rented, a digital camera.

It is rather unsatisfying to fool around with a camera unless you can form images on the sensor and therefore you need a lens. The cheap zoom lenses that come packaged with a Canon Digital Rebel or Nikon D50 kit are poor tools for building photography skills or making compelling images. The novice photographer who starts with a zoom lens typically uses it in lieu of backing up or stepping forward. An experienced photographer visualizes the scene first, chooses a focal length, then gets into the appropriate position to capture the scene with that focal length. It is much better to get a lens with a fixed focal length, learn to recognize scenes where that lens can be used effectively, and then add additional lenses once that focal length has been mastered. So even if you have the $1000+ to buy a high quality zoom and the muscles to lug it around it is probably a poor choice of first lens.

The $100-200 lightweight zoom lenses that come bundled with digital SLR bodies have some additional limitations. Being a good photographer starts with the ability to recognize a scene that looks attractive under its current lighting conditions. You need a lens with a wide enough maximum aperture, typically f/2.0 or f/1.4, to capture that scene even when the lighting is fairly dim, as it will be indoors or near the end of the day. An inexpensive zoom lenses will have a maximum aperture of between f/4.0 and f/5.6. At an aperture of f/5.6 you will need 8 times as much light to take a picture as you do at an aperture of f/2.0. Thus the cheap zoom will force you to use the on-camera flash, which casts an ugly flat light and in any case will render the scene completely different than it looked to your naked eye. Flash can be useful, especially with multiple strobes in the studio or as a fill-in light to reduce contrast outdoors, but mastering flash photography is a separate challenge.

The final problem with a cheap zoom lens is image quality. There is no free lunch in this world and when an optical engineer cuts cost and weight the sharpness and contrast are reduced. In fact, you might get a better quality photo with a point-and-shoot digicam than with a heavy expensive digital SLR with a cheap light zoom lens attached.

What you want for a starter digital camera lens is a high-quality "prime" lens with a fixed focal length. You want a "normal" perspective so that the relative sizes of objects in the image will be roughly what you experience with your normal vision. For a 35mm film camera or a full-frame digital SLR (Canon EOS-1Ds; Canon EOS-5D), the normal focal length is 50mm. For a Canon Digital Rebel or similar "big lenses/small sensor" camera the normal perspective is afforded by a 35mm lens. For a Four Thirds camera such as the Olympus E1, the normal lens is 25mm.

In the Canon system there are two kinds of autofocus motors available in the various lenses. The best kind of autofocus motor is ultrasonic, denoted by the "USM" designation on a lens. With USM the pure autofocus will be faster and it is also easier to let the camera do most of the focus work but manually change the point of focus if desired. For the EOS-1Ds or EOS-5D, I recommend the Canon 50/1.4 because it has the USM motor, unlike the cheaper Canon 50/1.8.

For the Canon small sensor DSLRs, e.g., the EOS 30D and Digital Rebel XTi, the Canon 35/2 lens is an economical lightweight choice, but sadly it lacks a USM motor. Canon makes a very fine 35/1.4L USM that lets you work in light only half as bright as the 35/2 (the "L" designation means that it is part of Canon's expensive lineup of lenses and will have superb optical performance and mechanical construction). This lens costs more than $1000, however, and, at 580 grams, is heavy. Generally speaking, "third party" lenses such as those made by Sigma, Tamron, and Tokina, are not worth considering compared to Canon-brand lenses. The remarkably cheap wide-range third-party zooms deliver terrible image quality. The high quality third-party prime lenses or fast zooms aren't much less expensive than high quality Canon- or Nikon-brand lenses. Sigma's 30/1.4 digital-only lens is an exception. Because it does not cast an image large enough to cover a 24x36mm film frame, the lens is much lighter (422g) than the Canon 35/1.4 and less than half the price (check it on Amazon now). It has an ultrasonic motor, denoted "HSM" by Sigma, and has delivered superb optical performance in magazine tests.

With Nikon, your choices are simple. Nikon doesn't make any full-frame digital SLRs, and they only make one 35mm prime autofocus lens, a 35/2. The Sigma 30mm f/1.4 EX DC for Nikon, $395 is probably a better choice due to its extra f-stop of light gathering capability and ultrasonic motor.

Olympus makes very few prime lenses and none with a 25mm "normal" perspective. Olympus does offer a choice of three zooms, however. The best image quality and fastest aperture is a 14-35/2.0. The "reasonably good" mid-range zoom is the 14-54/2.8-3.5. The cheapest Olympus zoom for the Four Thirds system is the 14-45/3.5-5.6, only suitable for sunny days due to its small maximum apertures.

As noted previously, expensive digital camera bodies are often sold in kits with cheap slow zoom lenses that sell separately for a maximum of $100. If the kit is the same price as the body alone, by all means get the kit and put the included lens aside until you are letting a clumsy child experiment with your camera system. But also shop for a high quality lens of some sort.

Distilled shopping advice:

• cheapest possible system: Nikon D40, 18-55mm kit, $429 (review)
• basic family camera system: Canon Digital Rebel XTi and Sigma 30/1.4 lens (buy it from amazon.com: body; lens)
• transitioning film photographer: Canon EOS-30D and Sigma 30/1.4 lens (buy it from amazon.com: body; lens)
• technophile: Canon EOS-5D and Canon 50/1.4 lens (buy it from amazon.com: body; lens)

Taken from http://photo.net