For example, a 50mm lens is considered normal for a 35mm SLR. But on a consumer digital camera with a fingernail-sized image sensor, a 50mm lens becomes a supertelephoto, equivalent to maybe 300mm on a 35mm camera. Put a 50mm lens on a 4x5 view camera, and it's an extreme wide-angle, equivalent to maybe 15mm on a 35mm camera (assuming it casts a large enough image circle to cover the 4x5-inch image area).
Any lens with a focal length shorter than the diagonal measurement of the image frame is considered wide-angle—for 35mm cameras, lenses shorter than 43mm are wide-angles, and for APS-C format D-SLRs, lenses shorter than 28mm are wide-angles. There are currently more than 60 lenses available with focal lengths of 28mm or shorter, giving even D-SLR users true wide-angle capability.
Chart - Representative Wide-Angle Lenses
Wide-Angles With D-SLRs
With the exception of the Canon full frame EOS-1DS Mark II and EOS 5, all of today's popular digital SLRs have image sensors that are smaller than a full 35mm film frame. These smaller image sensors see a smaller portion of the full image produced by the lens than a 35mm film frame (or full-frame image sensor) does, in effect cropping the image into what a somewhat longer lens sees on a 35mm camera. What this means to the wide-angle fan is that you need a shorter focal length at a given angle of view. When used on one of the popular APSC digital SLRs (so-called because their image sensors are about the size of an Advanced Photo System C-format film frame), a 28mm wide-angle lens sees what a 42mm lens on a 35mm SLR would see.
To deal with this factor, camera and lens manufacturers have designed a series of lenses specifically for these smaller sensors. Since these sensors are smaller, the lenses can be smaller, and smaller wide-angle lenses aren't as costly as those that must cover a full 35mm film frame. So you can choose from a whole variety of superwide-angle lenses and wide-angle zooms for very reasonable prices. As an added bonus, these APSC lenses send light to the image sensor more efficiently than lenses designed to cover 35mm film frames do.
Each manufacturer has a special designation for its APS-C lenses: Canon uses EF-S, Nikon and Tokina use DX, Pentax uses DA, Sigma uses DC and Tamron uses Di II. These lenses offer excellent results with the small-sensor D-SLRs, but bear in mind that they can't be used with 35mm or full-frame D-SLRs because their smaller image circles won't cover the whole image frame; they'll vignette.
Fish-eye lenses have an exceptionally wide angle of view, generally 180 degrees. There are two types: circular fish-eyes produce a round image in the rectangular image frame, and full-frame fish-eyes fill the frame, with a 180-degree angle of view measured diagonally (corner to corner). Note that circular fish-eyes produce round images with 35mm and full frame D-SLRs; when used on APS-C D-SLRs, the smaller image sensors crop in on the circular image, filling the frame.
Full-frame fish-eye lenses for full frame SLRs have focal lengths of 15- 16mm. There are also non-fish-eye superwide-angle lenses in this range. The difference is that "regular" superwide—angles are corrected for barrel distortion and in theory render straight lines as straight lines, no matter where they appear in the image frame. Fish-eyes render straight lines that go through the center of the image as straight lines, but bend lines that don't go right through the center outward: they do exhibit barrel distortion.
For 35mm cameras, superwide-angle lenses are those with focal lengths shorter than 24mm; lenses from 24mm to 43mm are just plain old wide-angles. This is an arbitrary classification, though; all are rectilinear (meaning they render straight lines as straight lines, no matter where they appear in the image), and the only difference is the field of view, the shorter ones taking in more of the scene spread before the camera. For APS-C-sensor D-SLRs, the dividing line is 16mm instead of 24mm (multiply the 35mm camera focal length by 0.67 to find the focal length that provides the equivalent field of view on an APS-C D-SLR). For the Olympus Four Thirds System D-SLRs, divide the 35mm camera focal length by two to find the focal length that will provide an equivalent field of view on Four Thirds cameras.
Using Wide-Angle Lenses
There are three main reasons why photographers use wide-angles: to include a vast vista in the image, to get subjects in the frame when space is limited and it's impossible to move the camera farther away, and to produce wide-angle distortion effects by moving very close to a subject.
When photographing wide vistas, remember that TTL metering might not work as it does with longer lenses. If you're shooting with a D-SLR, check the image on the LCD monitor after shooting it to confirm that the exposure is what you had in mind; if shooting film, bracket exposures until you get a feel for how your wide-angle lens works with your camera's metering system(s).
If you tilt a camera up or down, vertical objects at the sides of the image will tilt into the image. And if you don't hold the camera level horizontally, the horizon line will tilt. With longer focallength lenses, you might not notice this, but with their broad fields of view, wideangle lenses emphasize these effects. So keep the camera level (a tripod helps here) unless you specifically want tilted edge objects or horizon lines.
The elongated, distorted effect produced by moving in very close with a wide-angle lens is actually an accurate rendering of perspective for that shooting distance. The effect looks odd because we don't normally view subjects from such close range, but it's real. Perspective— the relative sizes of objects in a photo and the apparent distances between them—depends on the shooting distance. Move closer, and everything in the scene becomes larger, but nearer subjects "grow" faster than more distant ones, while the apparent distance between them increases: wide-angle distortion.
Conversely, if you move farther away, everything in the scene will get smaller, nearer subjects will shrink more rapidly relative to farther ones, and the apparent distance between them will decrease: the telephoto compression effect. This occurs regardless of the focal length of the lens on the camera— move far back with your wide—angle lens, then enlarge the central portion of the image on-screen or in a cropped print, and you'll get telephoto compression with your wideangle lens.
The expansion effect is most noticeable when wide-angle lenses are used because we generally move close to the subject when shooting with a wide-angle lens. And because of its wider angle of view, the wide-angle lens lets us movein closer than with a longer lens and still get the whole subject in the frame. Conversely, the compression effect is most noticeable when long lenses are used because we generally shoot from relatively far away when we use long lenses.
Like lenses, flash units have specific angles of coverage. If you're using flash with a wide-angle lens, check the specs to make sure the flash unit will cover what the lens sees—the area that will appear in the photo. Otherwise, you'll get a photo with a properly exposed central area and too-dark edges. Also, remember that illumination from direct flash falls off as the square of the distance: a subject twice as far from the camera as the properly exposed main one will be underexposed by two stops. The closer you move to a subject with the wide—angle lens and flash, the greater the exposure difference there will be between the main subject and background ones.
Depth Of Field
All other things being equal, wideangle lenses provide more depth of field than longer ones. That means that at the same focused distance and ƒ-number, a shorter lens will provide much more depth of field than a longer one. As noted, however, we generally move closer when shooting with a wide-angle lens, so all things aren't equal. At a given reproduction ratio (magnification) and ƒ-number, depth of field is the same for any focal length, assuming the lenses are all used on the same-format camera.
Stopping the lens down increases depth of field; in fact, the aperture is our most frequently used means of controlling depth of field. With a short lens, stopping the lens down results in very tiny apertures: While a 100mm lens at ƒ/22 has an aperture diameter of 4.5mm, a 10mm APS-C lens at ƒ/22 has an aperture diameter of just 0.45mm—less than 1/50 of an inch.
Such tiny apertures provide tremendous depth of field, but they also do something else: diffract the light waves (bend the waves around the edges of the tiny diaphragm opening) severely, which reduces fine detail. Diffraction is why those tiny lenses in consumer digital cameras rarely stop down beyond ƒ/8. It's also why you should stop a wide-angle lens all the way down only when maximum depth of field is essential to a shot; don't arbitrarily shoot everything at the lens' minimum aperture figuring that will produce the sharpest image: it won't.
|Fish Eye Alternative|
|If you're fascinated by fish-eyes
but don't want to invest hundreds of dollars in such a specialized-use lens, try a fish-eye converter, an attachment that screws into threads on the front of the camera lens and turns it into a quasi-fisheye. Adorama offers two Pro Optic Fisheye Auxiliary Lenses, a 0.42X version that produces circular images when attached to a 28mm camera lens and a full-frame fisheye effect on lenses of 40mm or longer, and a 0.25X version that produces a 180-degree angle of view when attached to a 50mm camera lens. The images aren't as sharp as those of a true fish-eye lens, especially at the edges, but the cost is minimal and the effect is interesting. Contact: Adorama, (800) 223-2500, www.adorama.com
See how it works with your wide—angle lens. Mount the camera on a tripod, focus carefully on a subject five feet away and shoot images at all the lens' apertures (adjusting the shutter speed accordingly to maintain correct exposure, of course). Then carefully focus on a subject 10 feet away and repeat the sequence. Examine the resulting slides, negatives or prints with a loupe or at 100% on screen for digital images. This will give you a good idea of how your lens performs at different apertures (and how clean your D-SLR's image sensor is; stopping a wide-angle lens all the way down brings any dust spots on the sensor into sharper focus, making them much more evident in photos).
Because the subject is generally smaller and there's more depth of field, it's harder to tell when the viewfinder image is at its sharpest when focusing a wide-angle lens manually. When autofocusing, make sure the active AF target is over the subject you want focused—it's easier to "miss" with a wide-angle's wider angle of view. It doesn't hurt to check the minimum focusing distance when comparing lenses because a longer minimum focusing distance limits your ability to maximize the wide-angle "distortion" effect—you can't move as close to the subject.
Minimum focusing distance refers to the distance from the subject to the focal plane (film plane or image sensor) when the lens is focused as close as it can focus. Minimum object distance is the distance from the subject to the front of the lens when the lens is focused as close as it can focus. Obviously, minimum object distance will be shorter than minimum focusing distance, something to keep in mind when comparing lens specs.