Small-Format Wide-Angle Zooms

The widely used APS-C-sized image sensor has helped make excellent D-SLRs affordable, but long carried a drawback for wide-angle photographers: a narrowed angle of view. Fortunately, camera and independent lens manufacturers now offer very short focal-length zoom lenses for these cameras, designed to eliminate this problem.

A full 35mm film frame measures 36x24mm, an area of 864 square millimeters. An APS-C image sensor measures 23.6×15.8mm (or thereabouts, depending on the camera), an area of just 373 square millimeters. The much smaller APS-C sensor, “sees” a lot less of the image projected at the image plane than a full 35mm film frame (or a “full-frame” digital image sensor) sees. The result? Any given lens used on a D-SLR with a smaller sensor frames as a lens that’s about 1.5x its focal length does on a 35mm camera: a 28mm wide-angle lens effectively becomes a 42mm not-so-wide one when attached to the D-SLR.

Put another way, with an APS-C-sensor D-SLR, you need a focal length 33% shorter to get the same field of view that a given lens yields when attached to a 35mm SLR. If you want the angle of view a 24mm lens provides on a 35mm SLR, you need a 16mm lens on the D-SLR.

The Solution

Camera manufacturers Canon, Nikon, Olympus, Pentax, Sigma and Sony all offer very short focal-length zoom lenses for their small-sensor D-SLRs. Fujifilm and Samsung don’t make lenses for D-SLRs, but their D-SLRs accept Nikon lenses and Pentax lenses, respectively.

Four Thirds System D-SLRs use even smaller 17.3×13.0mm image sensors, with a 2x focal-length factor. Olympus provides two very short focal-length zooms for Four Thirds System cameras, which include all Olympus D-SLRs, plus the Leica Digilux 3 and Panasonic Lumix DMC-L1.

But wait, there’s more. Independent lens makers Sigma, Tamron and Tokina produce very short focal-length zooms in mounts for many of these cameras, and Sigma’s also will fit Sigma D-SLRs. Thus, users of all current D-SLR models can do true wide-angle photography, regardless of the size of their camera’s image sensor.

A Bonus

These very short focal-length zooms offer benefits beyond providing true wide-angle shooting capability with smaller-sensor cameras. They also were designed specifically for the APS-C-sized image sensor (Four Thirds System lenses were designed specifically to work with the Four Thirds System image sensor). Since they don’t have to cover as large an area at the image plane, these lenses can be more compact than those designed to provide the same angle of view for a full 35mm film frame.

There are a few drawbacks, however. APS-C lenses can be used only on APS-C cameras—if you use them on a full-frame D-SLR or a 35mm SLR, they’ll vignette because they weren’t designed to cover such a large image area; and in some cases, they can’t physically be mounted on full-frame cameras. And because of their very short focal lengths, diffraction can adversely affect image sharpness at small apertures—ƒ/22 on a 10mm lens is just 0.45mm (1/56-inch) in diameter. Of course, the shorter focal lengths yield more depth of field, so there’s seldom a need to stop all the way down to ƒ/22.

So which are the APS-C lenses? The accompanying Wide-Angle Zoom Lenses For D-SLRs chart lists the current ones. You also can identify APS-C lenses by the code each manufacturer uses for those lenses that were designed specifically for use with the smaller-sensor D-SLRs: DA (Pentax), DC (Sigma), Di II (Tamron), DT (Sony), DX (Nikon and Tokina) and EF-S (Canon). Lenses with these designators can’t be used with film cameras or full-frame-sensor D-SLRs because vignetting would occur.

For Those Who Think
Really Wide…

Besides the nine rectilinear (“regular”) wide-angle zooms, two fisheye zooms are on the market. The Pentax smc-P-DA 10-17mm can be used with Pentax and Samsung D-SLRs; the Tokina AT-X 10-17mm DX is available in mounts for Canon, Nikon and Sony APS-format D-SLRs. These zooms provide an angle of view of 180 degrees (measured diagonally, at the 10mm setting) when used on these cameras, complete with the hallmark fish-eye barrel distortion: straight lines that don’t go right through the center of the image will be bowed out toward the frame edges.

Alphabet Soup

Lens manufacturers use a lot of different letter combinations in their lens names besides the aforementioned ones designating the APS-C-sensor optics. Here are some of significance to wide-angle photographers.

LD—Low-dispersion elements minimize chromatic aberrations and thus improve sharpness and color. They also reduce the need for additional elements, keeping lens size and weight down. Different manufacturers use different letters for their variants on the LD concept: ED, SD, SLD and S-UD are examples. All offer the same effect of sharper images with lighter lenses.

IF—Internal focusing offers several advantages. First, the front element doesn’t rotate during focusing, so orientation-sensitive lens attachments like polarizers and graduated filters stay put as you focus. Second, the physical length of the lens doesn’t change during focusing because only internal elements are moved. Thus, balance is better (this is of more concern with long lenses than wide-angles, but still nice). Finally, because smaller internal elements are moved instead of larger front ones, autofocusing can be quicker and more accurate. Rear focusing (RF) offers similar advantages

Asph—Aspherical elements reduce spherical aberrations and distortion, which means sharper images from center to edges and straighter straight lines at the edges of the image.

Small-Format Wide-Angle Zooms

Canon
Canon offers the EF-S 10-22mm ƒ/3.5-4.5 USM zoom for its APS-C D-SLRs. These include the EOS 20D and 30D, and all EOS Digital Rebel models (original, XT and XTi). Note that Canon’s EF-S lenses can’t be mounted on the discontinued EOS 10D, even though that camera has an APS-C sensor.

Because Canon’s APS-C sensors are slightly smaller than most, the focal-length factor is 1.6x instead of 1.5x. Thus, the EF-S 10-22mm lens frames like a 16-35mm zoom on a 35mm SLR—a superwide angle indeed.

Canon users also can choose among four wide zooms from independent lens makers: Sigma’s 10-20mm ƒ/4-5.6 EX DC, Tamron’s 11-18mm ƒ/4.5-5.6 Di II LD Aspherical (IF) and Tokina’s 12-24mm ƒ/4 AT-X AF PRO DX, plus Tokina’s 10-17mm ƒ/3.5-4.5 AT-X AF DX Fish-Eye zoom. The latter provides a 180-degree field of view (measured diagonally, at the 10mm setting), along with the expected fish-eye barrel distortion (i.e., straight lines that don’t go right through the middle of the image are curved toward the edges of the frame). Sigma also offers a 12-24mm ƒ/4.5-5.6 EX DG superwide zoom that can be used with digital and 35mm SLRs; its image circle covers a full 24x36mm image area.

Nikon
Nikon’s APS-C-format wide-angle zoom is the 12-24mm ƒ/4G ED-IF AF-S DX Zoom-Nikkor, which frames like an 18-36mm on a 35mm camera due to the 1.5x focal-length conversion factor of all Nikon D-SLR image sensors.

Nikon users also can choose among the same independent-lens makers’ wide zooms offered to Canon users—see the Canon section.
 

Fujifilm doesn’t make D-SLR lenses, but its FinePix S3 Pro and S5 Pro cameras accept Nikon-mount lenses, with the same 1.5x focal-length multiplier.

Olympus, Leica and Panasonic
All Four Thirds System cameras accept all Four Thirds System lenses. Currently, there are two really wide zooms for the format: Olympus’ 7-14mm ƒ/4.0 and 11-22mm ƒ/2.8-3.5 Zuiko Digital optics. Since the Four Thirds System image sensor is smaller than APS-C sensors, the focal-length conversion factor is 2x. Thus, the 7-14mm frames like a 14-28mm on a 35mm SLR, the 11-22 like a 22-44mm. Four Thirds System cameras currently include Olympus’s E-1, E-330 and E-500, Leica’s Digilux 3 and Panasonic’s Lumix DMC-L1.

Pentax and Samsung
Pentax offers both the smc-P-DA 10-17mm ƒ/3.5-4.5 ED-IF full-frame fish-eye zoom and smc-P-DA 12-24mm ƒ/4.0 ED AL (IF) wide zoom for its D-SLRs. Both lenses can be used with all Pentax D-SLRs, and because of the sensors’ 1.5x focal-length factor, frame like 15-26mm and 18-36mm zooms on a 35mm SLR.

Pentax D-SLRs also will accept the Pentax-mount version of Sigma’s 10-20mm ƒ/4-5.6 EX DC zoom and full-frame 12-24mm ƒ/4.5-5.6 EX DG zoom. Samsung’s D-SLRs take Pentax lenses, with the same 1.5x focal-length factor.

Sigma
Sigma’s 10-20mm ƒ/4-5.6 EX DC zoom comes in a mount for Sigma D-SLRs as well as Canon, Nikon and Pentax. Sigma’s D-SLRs (the SD9 and SD10 have been discontinued, but the new SD14 is due soon) have a 1.7x focal-length factor, so the 10-20mm frames like a 17-34mm on a 35mm SLR.

Sony
Sony offers the SAL 11-18mm ƒ/4.5-5.6 DT zoom, which was designed specifically for its DSLR-A100. The focal-length factor is 1.5x, meaning the lens frames like a 16.5-27mm on a 35mm SLR.

Sony D-SLRs accept Konica Minolta’s Maxxum-mount lenses, but none of those was designed specifically for APS-C image sensors. However, Sigma and Tamron produce Sony-mount versions of their 10-20mm and 11-18mm APS-C-format zooms, respectively, and these can be used on the A100 camera. Sigma’s full-frame 12-24mm ƒ/4.5-5.6 EX DG zoom also can be used.