Choosing the Lens or Amount of Zoom
A zoom lens lets you select how much of the setup to capture without moving the camera.
A polarizing filter will cut
reflections if the subject isn't metallic. Circular polarizing filters are required on autofocus
cameras. Sometimes polarizing filters are put on the studio lights.
A lens hood lets you block
light from the lens. Stray light can cause lens flare and lower image contrast.
Lens converters are available for many cameras that increase or decrease the focal length of the built-in zoom lens.
When using a camera that accepts interchangeable lenses you need a macro lens for close-up photography.
An extension tube fits between the camera and lens on a camera with interchangeable lenses.
Although a few digital cameras have interchangeable lenses, most come equipped with a built-in zoom lens that lets you choose any focal length within the range the lens is designed for. Lens focal lengths are based on the physical characteristics of the lens and the size of the film or image sensor. As image sensors get smaller, a given focal length lens magnifies more. Since there are a number of differently sized image sensors used in digital cameras, different focal lengths are needed to give the same image coverage on different cameras. Because of the confusion this causes, most digital camera companies give the actual focal length of their lenses and then an equivalent focal length were the lenses to be adapted to a 35mm camera. For example, a camera's lens may be described as 8.9mm to 71.2mm (equivalent to 35mm to 280mm on a 35mm camera).
When you change focal lengths, by zooming a lens or changing lenses, important effects are immediately obvious in the lens' angle of view, its magnifying power, its minimum focus distance, and its maximum shooting distance.
- Angle of view refers to how much of a setup the lens covers. Shorter focal length lenses have a wide-angle view that captures a wide expanse of a setup. As focal length increases, the field of view narrows and you can isolate smaller portions of the setup without moving closer.
- Magnification is related to the lens' angle of view. A short focal length lens
includes a wide sweep of the scene, so any object in the setup is reduced to fit into the image. A longer focal length gives a much narrower angle of view, so objects in a setup appear larger in the image.
- Minimum focus distance usually varies with focal length, especially with zoom lenses. The more you zoom out to decrease the lens' focal length, the closer you can get to the subject. If you can't focus, you may be too close for the lens or its current zoom setting.
- Maximum shooting distance refers to how far back you can get from a subject while still filling the image frame. Since getting too close can cause distortion (page 62), this can often be important.
On digital cameras, zoom often comes in two varieties-optical and digital. Optical zoom is performed by the lens and actually changes the amount of the scene falling on the image sensor. Every pixel in the image contains unique data so the final photo is sharp and clear. Digital zoom uses software and sleight of hand to take a small part of the image falling on the sensor and enlarging it to fill the sensor. It does this by adding new pixels to the image using sophisticated "guesswork" called interpolation. The interpolated image doesn't have as many unique pixels as one taken with an optical zoom so is inferior. In fact, you don't even need this zoom feature because you can get exactly the same effect, but with better results, by cropping a normal image in a photo-editing program and then enlarging it by resampling.
When photographing small objects such as coins or jewels, your lens' focal length and minimum focusing distance determines how large an object will be in the photograph. If you're photographing a small coin, you probably don't want it to appear as a tiny coin surrounded by a large background.
More likely you'd like a photo showing a large coin surrounded by a small background. For many setups, just zooming your lens in on the subject will suffice. However, macro mode or a macro lens allows you to get a lot closer to the subject, making it, or details of it, much larger in the final image. If you can't get close enough to an object to fill the image area, you can always crop out the unwanted areas later. However, the more you crop, the smaller the image will become.
When taking macro close-ups, if your camera's viewfinder doesn't show you the view through the lens, use the monitor to compose the image. If you don't, since the viewfinder is offset from the lens, the area seen in the viewfinder will differ from the area included in the image. Anything you expect to be in the center of the frame, won't be.
To get even closer to a subject, you can use other optical devices.
- Extension tubes fit between a removable lens and the camera body and allow the lens to focus much closer than normal, giving increased magnification. The larger the amount of extension, the greater the increase in magnification.
- Close-up lenses fit over the main lens and let you get closer to the subject. They magnify the subject without affecting aperture settings. These lenses come in a variety of enlarging powers (+1, +2, +3, and so on) and can be used individually or in various combinations. When using them in combinations, mount the higher power lenses closer to the camera lens.
With extension tubes, a pin smaller than a dime can be captured almost full-frame.