Lens Selection

Revision as of 01:56, 6 March 2007

General terms

focal length 

A physical property of any lens, referring to the strength with which the lens bends light; shorter focal lengths indicate a stronger bending of the light. It is most often referred to in terms of millimetres (mm), and "multiplied" for use on digital SLRs, most of which use a sensor that is smaller than 35mm (135 format) film. Common multiplication factors for modern digital SLRs (also referred to as the "crop factor") are 1.5 and 1.6, which when multiplied by the focal length can give a representation of the equivalent lens that would need to be used on a film SLR to achieve the same field of view. The focal length of the lens is independent of the camera to which it is mounted, but the crop factor is a useful metric for people migrating from film to digital to determine what lens would achieve the desired effect compared to their previous experience.

f-number 

The f-number is given in terms of f/# and refers to the physical size of the aperture of the lens as a fraction of its focal length, for standardisation of metering between lenses of differing focal lengths. The maximum f-number number is quoted once for prime lenses, and twice for some zoom lenses (e.g. "f/3.5-4/5",) being the maximum for each end of the zoom range. The lower the number, the greater the amount of light the lens will pass, and the shallower the depth of field.

Copy 

Think of each lens as a copy of an original 'master' lens somewhere deep in the Canon/Nikon/etc. labs. Unfortunately some "copies" are worse than others, so some people may refer to their lens as being a "good copy" or "bad copy".

Prime lens 

A "prime" lens has a fixed focal length, which greatly simplifies their design compared to zoom lenses. This simplification gives advantages such as larger maximum apertures and generally better optical quality for the same cost.

Zoom lens 

a lens with a variable focal length.

Telephoto lens 

Historically a lens which is physically shorter than its focal length, but now a term that is more commonly used to refer to lenses with focal lengths longer than a normal lens.

Wide angle lens 

A lens with a focal length shorter than "normal," that accordingly has a large - or wide - field of view.

"Normal" lens 

A lens with a focal length roughly equivalent to the film frame or sensor's diagonal measurement. These lenses are situated between the wide and telephoto lenses. Historically the normal lens on 35mm film was between 45mm and 55mm (although the diagonal of 35mm film measures 43mm) and the equivalent "normal" lens for use on most common digital SLRs can be in the range of 25-35mm depending on format.

Macro lens 

A lens with a very high magnification factor, achieved by a very close minimum focus distance. Macro lenses typically have magnification factors of greater than 1:2 (the image falling on the sensor/film is half of the actual size of the subject) and most dedicated macro lenses have magnification factors of 1:1 - allowing the subject to be captured on the film/sensor at life size - and are available in a range of (mostly long) focal lengths.

Fisheye lens 

A type of wide angle lens which produces a distorted image, hence the name.

Canon EF mount

The electronic focus mount used on Canon EOS film and digital SLR cameras. This supercedes the older FD-mount used on the older manual focus film SLR cameras. Some excellent and detailed reviews of many lenses from the EF range can be found at The Digital Picture.

Terms

USM 

Ultrasonic Motor - a fast and quiet auto-focus motor using ultrasonic waves (like Nikon's Silent Wave). Ring USM is an enhanced version of USM used on L-series lenses and some others (28-135 IS) with full-time manual focusing for manual focus re-touching meaning no need to physically switching between auto and manual focus modes.

IS 

Image Stabilization. The lense can compensate for small movements of a lens to maintain a sharp image - typically gives a three-stop advantage over non-IS lenses but doesn't make your subjects any more still.

DO 

Diffractive Optics - DO lenses are found with green rings (as opposed to the red ring around the L-series lenses) to set them apart. DO considerably cuts the size and weight of a lens down while maintaining quality. Still not as sharp as a true L lens but in many cases a viable alternative when size or portability are a concern. How DO works you can read at http://diffractive-optics.org/

L 

L-series professional lense in the Canon range. Most L-lenses offer far superior sharpness, contrast and build quality. Some are weather sealed, giving a fully weather sealed system when partnered with an EOS-1 series body. Most of the white lenses seen at sporting events are Canon L-series (white is used as the performance of flurite elements can be affected by heat).

Canon Lens Range

Zoom

• EF-S 10-22mm f/3.5-4.5 USM

A high quality and moderately expensive ultra-wide angle lens designed for some 1.6x crop digital SLRs (EF-S SLRs - 20D, 30D, 300D, 350D and 400D.)

• EF 17-40mm f/4L USM

A moderately expensive wide angle zoom, though representing more of a normal zoom on 1.6x crop digital SLRs. Optical quality is good, and build quality is excellent.

• EF-S 18-55mm f/3.5-5.6

Kit lens for EF-S SLRs. Optical and build quality are low, but it is very cheap and makes a good starting lens.

• EF-S 17-85mm f/4-5.6 IS USM

A moderately expensive general purpose lens designed for EF-S SLRs. Has IS, USM and better build quality, although optically it is not a big step up from the EF-S 18-55mm.

• EF 24-70mm f/2.8L

An expensive, high quality normal zoom lens originally designed for film cameras. The pinnacle of the Canon EF zoom line up in terms of sharpness and maximum aperture, at the cost of weight and size. when used on 1.6x crop digital SLRs, its wide end is no longer very wide.

• EF-S 17-55mm f/2.8 IS USM

An expensive, high quality normal zoom lens for EF-S SLRs. Optically one of the best zoom lenses available for those digital SLRs, however it combines an L-grade price with consumer-grade build quality.

• EF 28-135mm f/3.5-5.6 IS USM

Offers a wide range of focal lengths in a reasonably small package, and includes USM and Canon's first generation Image Stabiliser. Optical and build quality are reasonable, and it represents good value when used on 1.6x crop digital SLRs, although its wide end becomes more of a normal on these cameras, and becomes more of a telephoto zoom lens.

Primes

• EF 50mm f/1.8

A sharp, cheap lens with a very large aperture. Best bang for buck in the Canon range.

• EF 50mm f/1.4

• EF 50mm f/1.0L (discontinued)

• EF 50mm f/2.5 Macro

• EF-S 60mm f/2.8 Macro

• EF 135mm f/2.8L

• EF 200mm f/1.8L (discontinued)

Sigma Lens Range

Sigma is a third party lens manufacturer and builds lens with SIGMA, CANON EF, NIKON (D), MINOLTA, PENTAX mounts.

Terms

OS 

Optical Stabilizer. A built-in mechanism that compensates for small camera movements to keep sharp images when shooting hand held.

HSM 

Hyper-Sonic Motor. The AF is powered by an fast and quiet motor driven by ultra sonic waves. Similar to Canon's USM

EX 

EX Lens. This lens has been EX-finished to denote superior build and optical quality.

IF 

Inner Focus. This lens moves the inner lens group or groups without changing the lens' physical length.

ASP. 

Aspherical Lens.

APO 

APO Lens. This lens is made with special low-dispersion (SLD) glass and is designed to minimize color aberration.

DG 

DG Lens. This lens has a large aperture with wide angles and short minimal focusing ranges.

DC 

DC Lens. This lens' image circle matches the smaller size of the image sensor of most digital SLR cameras. Equivalent to the EF-S range in Canon Lenses.

Zoom

• 18-50mm f/2.8 EX

Great sharpness

• 24-70mm f/2.8 EX DG Macro

Good focal range, aperture, price (about $500) and decent sharpness at the cost of size (uses 82mm filters) and weight.

• 100-300 f/4 EX HSM

Extremely fast focusing and very sharp wide open. Sharpness drops a marginal amount past 220mm. Heavy lens, requires mono/tri pod for the best results

• 10-20 f/4-5.6 EX DC HSM

Very good lens. Sharp wide open throughout the range. Distortions are fairly well controlled above 15mm. Some copies are reported to have uneven sharpness (left side is sharper than right)

• 105 f/2.8 EX Macro

Sharp, sharp and even more sharp. Slow focusing due to no HSM, but MF is easy to use. Dual Clutch system can be fiddle. Very nice metal hood.

Prime

• 50m f/2.8 - Macro EX DG

Very sharp lens at a reduced cost. Uses 55mm filter and has a really short focus range of 18.5 cms. Commes with a sun hood.

Nikon F mount

Nikon's F-mount film bodies (eg, F70. F6) and digital SLR bodies (D100, D1X, D2H, D70, D50 etc) take Nikon (or otherwise known as Nikkor) F-mount lenses. The flexibility of the F-mount is such that you can still aquire manual focus lenses which are still compatible with the newer AF bodies and digital SLRs. If you choose to use a manual focus lens on an AF body, you'll lose important features such as metrix metering and other automation.

Terms

G 

Electronically controlled aperture (other Nikkor lenses will have an aperture ring allowing physical, manual aperture control useful for the older bodies)

DX 

Digital SLR compatible only. Similar to EF-S in Canon land but yet different, as it will work with any DX-format (APS-C 1.5x crop factor) SLR, which includes the entire range of digital Nikon SLRs from the D40 right up to the D2X. While they will still work with a non-DX format camera, Nikon does not recommend it.

ED 

Stands for Extra Low Dispersion Glass. It is basically a glass coating that doesn't disperse light as it enters the lens as normal glass does.

D 

Lens equipped with a "chip" which allows the camera body to assess the distance of the object being photographed and expose for that object correctly.

IF 

Internal focusing - CPU controlled focusing performed by a CPU in the lens itself as opposed to gearing to the lens mount of the camera. The result is a far superior focusing speed.

AF 

Auto-focus.

AF-S 

Silent-wave auto-focus. Similar to Canon's USM.

VR 

Vibration Reduction. Image Stabiliser technology allowing a photographer to shoot three-stops lower than without VR.

Pentax K mount

Pentax have used the K mount on all of their 35mm film SLRs and Digital SLRs since the introduction of the mount in 1975. The K mount on the DSLRs is compatible with all Pentax K mount lenses and many third Party lenses.

Terms

K 

Is the first generation K mount lens, Manual Focus, Manual Exposure.

M 

Second generation of K mount lens, smaller then their K counterparts, manual focus manual exposure

A 

First Auto exposure lenses from Pentax, manual focus.

F 

First generation Auto Focus, Auto exposure lens

FA 

Second generation Auto Focus, Auto Exposure lens, On board chip contains lens MTF data for Hyper Program compatible bodies

FA-J 

Similar to FA lenses but don’t have an aperture ring.

DA 

Digital Lenses, no aperture ring, some have reduced images circle some don’t, Digital coatings and optimised construction.

D-FA 

Digital Lenses, aperture ring, covers a 35mm frame. Digital coatings and optimised construction.

* (star) lens 

Pentax’s equivalent to Canon’s L, lenses of exception quality. (A, F, FA)

DA* 

Pentax’s High spec Digital lenses, Exceptional quality, weather sealed, SDM (Super Sonic Direct drive motors)

Limited 

A prime lens of unparalleled image quality and construction, hand made to the highest quality.

AL 

A lens that uses one or more aspherical elements to help improve wide angle performance and sharpness.

ED 

A lens that uses extra-low dispersion glass elements reduces Chromatic aborations.

IF 

A lens that uses an internal focusing mechanism.

Fixed Rear Element Extension (FREE) 

A lens whose last element group remains fixed during focusing.

SMC 

Pentax’s Lens coating technology.

Quick Shift 

Allows Manual adjustment of AF after AF lock has been achieved.

PZ 

Power Zoom, and Electronic zoom function on KAF-2 mount FA lenses, only functional on Z series FSLRs and K10D digital body.

Information courtesy of Bojidar Dimitrov's Pentax K-Mount Equipment Page http://www.bdimitrov.de/kmp/