Lens Components

The lens shown at left in Figure 3.31 is a typical lens that might be mounted on a Nikon dSLR. Unfortunately, this particular lens doesn’t include all the common features found on the various Nikon lenses available for your camera, so I am including a second lens (shown at right in the figure) that does have more features and components. It’s not a typical lens that a D7000 user might work with, however. This 17-35mm zoom is a pricey “pro” lens that costs about half as much as the entire D3100 camera. Nevertheless, it makes a good example. Components found on this pair of lenses include:

• Filter thread. Most lenses have a thread on the front for attaching filters and other add-ons. Some, like the 18-55 VR kit lens shown, also use this thread for attaching a lens hood (you screw on the filter first, and then attach the hood to the screw thread on the front of the filter). Some lenses, such as the AF-S Nikkor 14-24mm f/2.8G ED lens, have no front filter thread, either because their front elements are too curved to allow mounting a filter and/or because the front element is so large that huge filters would be prohibitively expensive. Some of these front-filter-hostile lenses allow using smaller filters that drop into a slot at the back of the lens.

  Figure 3.31.

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• Lens hood bayonet. Lenses like the 17-35mm zoom shown in the figure use this bayonet to mount the lens hood. Such lenses generally will have a dot on the edge showing how to align the lens hood with the bayonet mount.

• Focus ring. This is the ring you turn when you manually focus the lens, or fine-tune autofocus adjustment. It’s a narrow ring at the very front of the lens (on the 18-55mm kit lens), or a wider ring located somewhere else.

• Focus scale. This is a readout found on many lenses that rotates in unison with the lens’s focus mechanism to show the distance at which the lens has been focused. It’s a useful indicator for double-checking autofocus, roughly evaluating depth-of-field, and for setting manual focus guesstimates. Chapter 11 deals with the mysteries of lenses and their controls in more detail.

• Zoom setting. These markings on the lens show the current focal length selected.

• Zoom ring. Turn this ring to change the zoom setting.

• Autofocus/Manual switch. Allows you to change from automatic focus to manual focus.

• Aperture ring. Some lenses have a ring that allows you to set a specific f/stop manually, rather than use the camera’s internal electronic aperture control. An aperture ring is useful when a lens is mounted on a non-automatic extension ring, bellows, or other accessory that doesn’t couple electronically with the camera. Aperture rings also allow using a lens on an older camera that lacks electronic control. In recent years, Nikon has been replacing lenses that have aperture rings with versions that only allow setting the aperture with camera controls.

• Aperture lock. If you want your D7000 (or other Nikon dSLR) to control the aperture electronically, you must set the lens to its smallest aperture (usually f/22 or f/32) and lock it with this control.

• Focus limit switch. Some lenses have this switch (shown in Figure 3.32), which limits the focus range of the lens, thus potentially reducing focus seeking when shooting distant subjects. The limiter stops the lens from trying to focus at closer distances (in this case, closer than 2.5 meters).

  Figure 3.32. Some lenses have focus limit switches and controls for vibration reduction (VR) features.

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• Vibration reduction switch. Lenses with Nikon’s Vibration Reduction (VR) feature include a switch for turning the stabilization feature on and off, and, in some cases, for changing from normal vibration reduction to a more aggressive “active” VR mode useful for, say, shooting from moving vehicles. More on VR and other lens topics in Chapter 11.

The back end of a lens intended for use on a Nikon camera has other components that you seldom see (except when you swap lenses), shown in Figure 3.33, but still should know about:

• Lens bayonet mount. This is the mounting mechanism that attaches to a matching mount on the camera. Although the lens bayonet is usually metal, some lower-priced lenses use a rugged plastic for this key component.

  Figure 3.33.

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• Automatic diaphragm lever. This lever is moved by a matching lever in the camera to adjust the f/stop from wide open (which makes for the brightest view) to the taking aperture, which is the f/stop that will be used to take the picture. The actual taking aperture is determined by the camera’s metering system (or by you when the D7000 is in Manual mode), and is communicated to the lens through the electronic contacts described next. (An exception is when the aperture ring on the lens itself is unlocked and used to specify the f/stop.) However, the spring-loaded physical levers are what actually push the aperture to the selected f/stop—even with advanced cameras like the D7000 or D3s. The aperture lever is also activated when you press the DOF button.

• Electronic contacts. These metal contacts pass information to matching contacts located in the camera body allowing a firm electrical connection so that exposure, distance, and other information can be exchanged between the camera and lens.

• Lens type signal notch. This is a machined groove in the lens mount, designed to tell older (non-dSLR) cameras that the aperture stops were linear. Today, this information would be conveyed electronically, except that all current lenses already have linear f/stops.

• Indexing cutout. The base of any Nikon lens made after 1977 that has an aperture ring includes a cutout notch that mates with a ring around the lens mount of Nikon’s advanced cameras (D200, D300/D300s, D2x/D2xs/D3/D3s/D3x/D700, and some older pro models). It tells the camera what the maximum aperture is and what f/stop has been set. For a D7000 owner, this means that older manual focus lenses (including pre-1977 lenses that have been converted to this system) can be used for automatic metering with the Aperture-priority exposure mode, and for manual metering in Manual exposure mode.

• Autofocus drive screw slot. (Not shown in the figure.) As you’ll learn in Chapter 11, older autofocus lenses (given the AF designation in Nikon nomenclature) lack an internal autofocus motor. Focus is set using a screw drive built into the camera body of every Nikon autofocus camera (film or digital) except (at the time I write this) the Nikon D40/D40x, D60, D3000, D3100, D5000, and D5100. Lenses given the AF-S designation lack this connection, because autofocus is achieved internally using a tiny motor.