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Sunday, April 1, 2007

Small-Format Wide-Angle Zooms


You don't need a "full-frame"-sensor D-SLR to do wide-angle photography


The Problem
APS-C Lens Main Advantages
  • Wide-angle capability with APS-C sensor D-SLRs
  • Optimized specifically for APS-C sensors
  • Relatively compact
APS-C Lens Disadvantages
  • Can't be used on 35mm or "full-frame" D-SLRs
  • Diffraction can reduce image quality at the smallest aperture settings
Tip For The Budget-Minded
The really wide-angle zoom lenses for smaller-sensor D-SLRs start around $500.
If you're on a tight budget and want wide-angle capability, check out the "standard" zooms often sold with these cameras. These 18-55mm (or thereabouts) lenses sell for under $200 (closer to $100 if purchased in a kit with the camera body), and that 18mm
focal length is equivalent
to 27mm on a 35mm SLR—definitely wide-angle

A full 35mm film frame measures 36x24mm, an area of 864 square millimeters. An APS-C image sensor measures 23.6x15.8mm (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? Anywide-angle lenses 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 17.3x13.0mm 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.

Focal-Length Equivalency Table
If you want the field of view of this focal length a on a 35mm SLR Use this focal length on a D-SLR with a 1.5x factor Use this focal length on a D-SLR with a 1.6x factor Use this focal length on a D-SLR with a 1.7x factor Use this focal length on a D-SLR with a 2.0x factor
15mm 10mm 9.4mm 8.8mm 7.5mm
18mm 12mm 11.2mm 10.6mm 9mm
20mm 13.4mm 12.5mm 11.8mm 10mm
24mm 16mm 15mm 14mm 12mm
28mm 18mm 17.5mm 16.5mm 14mm
35mm 24mm 22mm 20.6mm 18mm
You can see from this table that you need a focal length of 18mm or shorter to get a really wide-angle effect with a smaller-sensor D-SLR.

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.

WIDE-ANGLE ZOOM LENSES FOR D-SLRS

Lens

Filter
Size (mm)

Elements/ Groups
(special elements)

IF/Rear
Focusing

Format

Min. Focus
(in.)/Magnif.

Diameter
& Length (in.)

Weight
(oz.)

List Price

Fisheye Zooms

Pentax smc-P-DA 10-17mm ƒ/3.5-4.5 ED-IF Fisheye

none

10/8 (ED)

IF

APS-C

5.5/1:2.6

2.7x2.8

11.3

$541

Tokina AT-X 10-17mm ƒ/3.5-4.5 AF DX Fish-Eye

none

10/9 (SD)

n/a

APS-C

5.5/1:2.6

2.8x2.8

12.3

$535

Wide-Angle Zooms

Canon EF-S 10-22mm ƒ/3.5-4.5 USM

77

13/10 (SUD, Asp)

IF

APS-C

9.6/1:4.2

3.3x3.5

13.6

$775

Nikon 12-24mm ƒ/4G ED-IF AF-S DX Zoom-Nikkor

77

11/7 (ED, Asp)

IF

APS-C

11.8/1:8.3

3.2x3.5

17.1

$1,099

Pentax smc-P-DA 12-24mm ƒ/4.0 ED/AL (IF)

77

13/11 (ED, Asp)

IF

APS-C

12/1:8.3

3.3x3.4

15.2

$710

Sigma 10-20mm ƒ/4-5.6 EX DC

77

14/10 (SLD, Asp)

IF

APS-C

9.4/1:6.7

3.3x3.2

16.6

$473

Sony SAL 11-18mm ƒ/4.5-5.6 DT

77

15/12 (ED, Asp)

IF

APS-C

9.6/1:8

3.3x3.2

12.7

$649

Tamron 11-18mm ƒ/4.5-5.6 Di II LD Aspherical (IF)

77

15/12 (LD, Asp)

IF

APS-C

9.8/1:8

3.3x3.1

12.5

$490

Tokina 12-24mm ƒ/4 AT-X AF PRO DX

77

13/11 (SD, Asp)

IF

APS-C

11.8/1:8

3.3x3.5

20.1

$450

For Four Thirds System

Olympus 7-14mm ƒ/4.0 Zuiko Digital

none

18/12 (SED, ED, Asp)

n/a

4/3

9.75/1:9.1

3.4x4.7

27.9

$1,594

Olympus 11-22mm ƒ/2.8-3.5 Zuiko Digital

72

12/10 (Asp)

no

4/3

11.0/1:7.7

2.9x3.6

17.1

$720

Notes
This is a sampling of wide-angle zoom lenses, not necessarily a complete list ED, LD, SD, SED, SLD and SUD are low-dispersion elements; see text APS-C format indicates a lens designed for use with D-SLRs having APS-C-size image sensors; can't be used with full-frame sensors or 35mm SLRs 4/3 format indicates a lens designed for use with Four Thirds System D-SLRs n/a = information not available at press time

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.


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