Working with Lenses

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If Canon has one advantage over many of the other vendors of digital SLRs (other than making great, affordable cameras), it's the mind-bending assortment of high quality lenses available to enhance the capabilities of cameras like the Canon EOS 40D. Thousands of current and older lenses introduced by Canon and third-party vendors since 1987 can be used to give you a wider view, bring distant subjects closer, let you focus closer, shoot under lower light conditions, or provide a more detailed, sharper image for critical work. Other than the sensor itself, the lens you choose for your dSLR is the most important component in determining image quality and perspective of your images.

This chapter explains how to select the best lenses for the kinds of photography you want to do.

But First, a Word from Our Sensor

One pervasive consideration that will trip us up in this chapter (and throughout this book) is the omnipresent lens crop factor. If the sensor is smaller than the standard 35mm film frame (24mm X 36mm), then any given lens will produce a field of view that's cropped from that full frame. To express the "real" field of view in 35mm terms, you must multiply a lens's focal length by the crop factor, which in the case of the EOS 40D is 1.6X. Canon also sells dSLRs with 1.3X and 1X (full-frame) sensors, which provide the fields of view shown in Figure 6.1. At this writing, Canon's camera line includes the Canon EOS-1Ds Mark III and Canon EOS 5D, which both provide a full-frame, 1X crop (or non-crop) of the image, compared to a film camera. The Canon EOS-1D Mark III offers a 1.3X crop, while the Canon EOS 40D and the Digital Rebel models use a 1.6X crop of the full-frame sensor area.

Canon offers digital SLRs with full-frame (1X) crops, as well as 1.3X and 1.6X crops.

If you're accustomed to using full-frame film cameras, you might find it helpful to use the crop factor "multiplier" to translate a lens's real focal length into the full-frame equivalent, even though nothing is actually being multiplied. Throughout most of this book I've been using actual focal lengths and not equivalents, except when referring to specific wide-angle or telephoto focal length ranges and their fields of view.

Your First Lens

Some Canon dSLRs are almost always purchased with a lens. The Digital Rebel and Digital Rebel XT/XTi, for example, are often bought as entry-level cameras, frequently by first-time SLR or dSLR owners who find the Canon EF-S 18-55mm f/3.5-5.6 autofocus lens an irresistible bargain at about $100 over the cost of the camera body alone. Other Canon models, including the EOS 1D, EOS 1Ds, and EOS 5D, are generally purchased without a lens by veteran Canon photographers who already have a complement of optics to use with their cameras.

The Canon EOS 40D falls somewhere in between. I bought mine as a body-only, because I already had a collection of lenses. But you might have purchased your 40D with a lens, because it's an excellent first Canon camera for photographers experienced with another camera line, or for ambitious beginners. That makes an economical "kit" lens very attractive. However, you'll also find many purchasers who, like me, fall into one of the following categories: Those who are upgrading from the Digital Rebel models or an EOS 10D/20D/30D; from a Canon film camera; or who are buying the 40D as a second camera body to complement their Canon EOS 1D, or even as an adjunct to their full-frame IDs or 5D cameras. These owners, too, generally have lenses they can use with their new 40D.

So, depending on which category you fall into, you'll need to make a decision about what kit lens to buy, or decide what other kind of lenses you need to fill out your complement of Canon optics. This section will cover "first lens" concerns, while later in the chapter we'll look at "add-on lens" considerations.

When deciding on a first lens, there are several factors you'll want to consider:

■ Cost. You might have stretched your budget a bit to purchase your EOS 40D, so you might want to keep the cost of your first lens fairly low. Fortunately, there are excellent lenses available that will add from $100 to $300 to the price of your camera if purchased at the same time.

■ Zoom range. If you have only one lens, you'll want a fairly long zoom range to provide as much flexibility as possible. Fortunately, the two most popular basic lenses for the 40D have 3X to 5X zoom ranges, extending from moderate wide-angle/normal out to medium telephoto. Either are fine for everyday shooting, portraits, and some types of sports.

■ Adequate maximum aperture. You'll want an f/stop of at least f/3.5 to f/4 for shooting under fairly low light conditions. The thing to watch for is the maximum aperture when the lens is zoomed to its telephoto end. You may end up with no better than an f/5.6 maximum aperture. That's not great, but you can often live with it.

■ Image quality. Your starter lens should have good image quality, because that's one of the primary factors that will be used to judge your photos. Even at a low price, the several different lenses sold with the 40D as a kit include extra-low dispersion glass and aspherical elements that minimize distortion and chromatic aberration; they are sharp enough for most applications. If you read the user evaluations in the online photography forums, you know that owners of the kit lenses have been very pleased with its image quality.

■ Size matters. A good walking-around lens is compact in size and light in weight.

■ Fast/close focusing. Your first lens should have a speedy autofocus system (which is where the ultrasonic motor/USM found in all but the bargain basement lenses is an advantage). Close focusing (to 12 inches or closer) will let you use your basic lens for some types of macro photography.

You can find comparisons of the lenses discussed in the next section, as well as third-party lenses from Sigma, Tokina, Tamron, and other vendors, in online groups and websites. I'll provide my recommendations, but more information is always helpful.

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