Lens choice

From Nikonians Wiki

A photographer chooses a lens to produce a particular optical result. However, the factors which lead to a lens being suitable are not only optical, but also physical, mechanical, electronic and financial.

Nikon sets out the key characteristics of most lenses in its nomenclature, eg 70-200 f2.8 VR AF-S ED

Optical characteristics

The key optical characteristics are

• Focal length, or, for a zoom, range of focal lengths, eg, 70-200
• Maximum aperture, eg, f2.8. A lens with a wide maximum aperture is known as a fast lens, while a lens with a narrower maximum aperture is known as a slow lens.
• aberration
• acutance
• format, either general for all 35mm photography, or DX, meaning exclusively for DX type sensors, not for FX sensors or film.
• boke is a result of a lens mechanical characteristic, being the type of iris diaphragm, but is often considered as an optical characteristic of the entire lens system

ED specifies that the lens is fitted with Extra-low dispersion glass

N specifies that the lens is fitted with nano-coated glass

• rectilinear or fisheye. Most lenses are rectilinear, but a lens specified as fisheye has not been corrected for curvature, and is therefore able to produce extremely wide angles with a distinctive linear distortion
• lenses with CRC (Close Range Correction System) are corrected for use at close distances, such as micro. However, some very wide lenses, such as the 10.5 DX fisheye also have CRC, as well as a few medium range telephoto lenses.
• catadioptric lenses, designed using a mirror are also known as reflex lenses.

Physical characteristics

Physical characteristics are principally size and weight, but also include

• mount — not all Nikon F-mount cameras can be physically fitted with all Nikon F-mount lenses
• controls — Nikon G type lenses do not have physical aperture rings, and therefore can only be used on cameras which set the aperture electronically
• presence of a tripod collar — highly useful for long lenses where mounting the lens on the tripod rather than mounting the camera improves centre of mass and reduces strain on the lens mount
• ergonomics — some users prefer push-pull "one touch" zoom lenses, while most prefer to have two rings for focus and zoom
• type of lens hood. Lens hoods are extremely important for protecting the lens and the image

Mechanical characteristics

• Autofocus lenses are either screw-type or silent wave, specified as AF-S. Silent wave lenses have motors fitted in the lens, and allow the user to turn the focusing ring without switching to manual focus. They are also faster. The Nikon D40 and Nikon D40X can only autofocus with AF-S lenses.
• The iris diaphragm type sets the boke. Some types of diaphragm on older lenses are particularly susceptible to oil on the blades.
• micro capability, in dedicated micro lenses specified as 'micro' in the lens name, which refers to an optical-mechanical design capable of focusing at close distances, and therefore able to reach 1:1 magnification
• movements, such as tilt and shift, are generally designated as PC for perspective correction, or tilt/shift for a fuller set of movements
• defocus control, specified as DC, allows the photographer to selectively defocus the front and/or the rear of the image, to achieve optimal boke
• internal focus or IF lenses do not rotate the front element as they focus, which is important if using optical filters
• prime lenses are fixed focal length, whereas zoom lenses have complex mechanisms for moving the optical elements to change the focal length. Zoom lenses are either constant aperture or variable aperture. Professional lenses are constant aperture, which means their maximum aperture remains the same through the zoom range. This makes for a physically larger lens. Variable aperture lenses are typically one stop or EV slower at their longest focal length than at their shortest.

Electronic characteristics

• Automatic indexing, AI and later lenses including all AF lenses transmit aperture information to the camera, although not all dSLR cameras are able to make full use of all the information that AIS sends
• AI-S lens, for Automatic index - shutter, provide additional information.
• AF (Autofocus) lenses are autofocus lenses, which work together with the autofocus electronics in the camera
• AF-D lens additionally transmits distance information to the camera, for 3D Color Matrix Metering
• AF-S lens is an autofocus lens with silent wave motors. See above.
• VR lenses, for vibration reduction, contain a voice coil which responds to shake and works to minimise it

Financial characteristics

The total cost of ownership of a lens is the purchase price, less the resale value, plus maintenance costs, and, crucially, the cost of not having the lens while it is being maintained, or the cost of the hire of a lens while away. Nikon Professional lenses are eligible for a fast-track Nikon service in many countries. Nikon publishes lists of its professional lenses, but, generally speaking, all constant aperture zoom lenses, all wide aperture prime lenses, and all specialist lenses such as DC (Defocus Control), PC and fisheye are considered to be 'professional'. NPS, or Nikon Professional Services, offers its members a fast-track repair on all equipment, as well as (in some cases) rental or loan of replacement equipment. NPS membership is available to professional photographers possessing a certain amount of professional equipment, typically two pro bodies and three pro lenses, although this may vary from country to country.

• This page was last modified on 27 June 2010, at 06:59.
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