Choosing a Prime Lens


      Most people buy an interchangeable-lens camera with at least one zoom lens ““ and for many people one or two kit lenses is all they’ll need. That said, serious photographers also understand that zoom lenses are essentially compromises. They aren’t as fast as prime lenses and their optical performance is seldom as good.


      SMC Pentax-DA 50mm f/1.8 Lens  

      Prime lenses provide the best image quality and wider maximum apertures than zoom lenses, particularly at longer focal lengths.   However, prime lenses are usually quite a bit heavier than typical zoom lenses and most of them are more expensive so you need to think carefully about the improvements they will make to your photography before investing in one or more of these lenses.

      It makes sense to have zoom lenses in your kit because you would find it expensive to cover a normal range of focal lengths without including at least one zoom lens.   In addition, your camera bag would need to be a lot larger and more substantial and would become much heavier to carry.

      But there is a good argument to consider at least one prime lens, particularly when you are interested in a particular photographic genre. In this feature we’ll consider the main reasons for investing in a prime lens outline a few subject types where it will be worthwhile.

      Will you notice the difference?

      This question should be foremost whenever you consider purchasing any new piece of equipment. If you won’t be able to see any difference between shots taken with your existing camera and lens set and those taken with a new body or lens, there’s no real point in upgrading.

      However, there are a couple of areas on which a fast prime lens will make a noticeable difference to your photography:

      1. The viewfinder image will be brighter, making it easier to focus manually and/or ensure autofocused subjects are sharp. This can make a huge difference when shooting in low light levels.
      2. There will be more scope for shooting with a very shallow depth of field. The wider the maximum aperture of the lens the greater the degree of blurring in areas that are out-of-focus. Prime lenses also tend to have softer and more natural-looking bokeh than zoom lenses.
      3. Aberrations are generally fewer in prime lenses because it’s easier to design the optical system to eliminate them. Consequently, you will probably see some differences in image sharpness (particularly edge-to-edge sharpness) and contrast when making A3 or larger prints.

      There are three main subject types where buying prime lenses is easily justified: macro, portraiture and architectural photography. Wildlife photographers can also benefit from shooting with fast prime lenses, largely because it’s easier to focus on flighty subjects when the viewfinder image is bright. In addition, a case can be made for using prime lenses for architectural photography and some kinds of landscape photography, although it’s not quite as compelling for the latter.

      Prime Lenses for Macro

      True macro photography refers only to ‘life-size’ reproduction ““ which means a 1:1 reproduction (magnification) ratio ““ or slightly larger. It’s almost impossible to obtain such reproduction ratios with zoom lenses, the best of which will seldom go larger than half life size.

      All macro lenses should provide very sharp images so the best way to decide on a lens is on the basis of working distance (the distance between the front of the lens and the subject when the lens is at its closest focus). In general, the longer the focal length of the lens, the greater the working distance it provides.

      Most lens manufacturers don’t publish working distances but it’s easy enough to calculate the working distance. Simply subtract the length of the lens and the distance between the rear element of the lens and sensor (around 44mm for most DSLRs) from the published closest focusing distance for the lens.

      For static (non-moving) subjects, such as flowers or coins, a relatively short focal length will be fine. For subjects that are easily ‘spooked’, such as insects and small animals, the longer the working distance the more likely you are to get a usable shot.

      With shorter focal lengths the lens may throw a shadow over the subject and it can be difficult to photograph subjects among grass or leaves. On the plus side,   shorter focal lengths often add a sense of depth to the shot, whereas longer lenses tend to flatten the view.



      Sigma’s 105mm macro lens is available with mounts for all major DSLR brands and provides a useful working distance of 121mm.

      Prime Lenses for Portraiture

      Photographers usually choose prime lenses for portraiture for the following reasons:  

      1. The focal length selected provides a comfortable   working distance between the camera and the subject.
      2. The lens provides a natural-looking perspective at the selected shooting distance.
      3. The aperture is wide enough to provide plenty of depth-of-field control and attractive bokeh.

      Although short zooms, such as 70-200mm, cover the most popular range of focal lengths, you’ll pay a lot for a fast f/2.8 maximum aperture and the lens will be large and bulky. Once you’ve determined the style of portraiture you prefer, a prime lens will provide better performance.

      Most portrait photographers prefer a working distance of three to five meters between their camera and the subject. It’s close enough to support good communication without making the subject feel crowded and/or dominated.

      Consequently, the classic focal length range for portrait lenses on camera with a 36 x 24mm sensor is from around 80mm to 135mm. For cameras with APS-C sized sensors, it is 50mm to around 85mm and for Four Thirds system sensors it’s 40mm to 65mm.

      Shorter focal lengths can be used for portraits in which the subject fills less than a quarter of the frame (as in ‘environmental’ portraits). Longer lenses tend to ‘flatten’ the subject and, although they’re great for candid shots and street photograph, in a studio situation you need plenty of space to use them. However, they can produce interesting results and usually have attractive bokeh.

      Interestingly, you can also use macro lenses for portraiture, because they are fast and sharp and provide a good working distance for ‘head shots’.   And if the subject isn’t framed as you like it,   ‘zooming with your feet’ can bring you closer or further away from the subject in just a few steps.



      Tamron’s 60mm macro is one of a number of macro lenses that can double as portrait lenses. Fitted to a camera with an APS-C sized sensor, it provides an effective focal length of around 90mm, which is ideal for head-and-shoulders shots.

      Recommended Portrait Lenses

      The following lenses can be used on DSLRs with 36 x 24mm sensors and smaller APS-C sized sensors. They are competitively priced and good performers for portraiture.

      Canon EF 85mm f/1.8 USM: Excellent value for money at $719 (RRP) and usable with all Canon DSLRs. Focal length is equivalent to 135mm on cameras with APS-C sized sensors.

      Nikon AF Nikkor 85mm f/1.8D: Priced at less than $600 this compact, lightweight lens provides a focal length equivalent to 127.5mm on cameras with APS-C sized sensors.
       Sigma 85mm f/1.4 EX DG HSM: A slightly more expensive (but faster) lens with mounts for all major DSLR brands. For cameras with APS-C sensors, a dedicated hood adapter, which expands the length of the lens hood is supplied.

      Zeiss Planar T* 85mm f/1.4:  A fast, high-quality lens available with mounts to suit Nikon F bayonet (ZF), Canon EF bayonet (ZE) and Pentax K bayonet (ZK) lens mounts. Usable with ‘full-frame’ and APS-C DSLR cameras

      Macro lenses that can be used for portraiture include:
       Canon EF-S 60mm f/2.8 Macro USM: A dynamic, compact, fast-focusing lens  that provides attractive bokeh for portraiture.

      Nikon AF Micro-Nikkor 60mm f/2.8D: Another macro lens that doubles as a compact portrait lens.  

      Sigma Macro 70mm f/2.8 EX DG: Available with mounts for all major DSLR brands, this lens provides an effective focal length of around 105mm on cameras with APS-C sensors.

       Tamron SP AF 90mm f/2.8 Di Macro: A new version of a popular macro lens that is popular with portrait photographers.  Available with mounts for all major DSLR brands.

      Prime Lenses for Wildlife Photography

      Although some wildlife photographers can make do with zoom lenses, if you’re really serious about photographing   birds or animals in the wild, a long telephoto lens is a must. But you must be prepared to invest serious money if you want a fast lens with a focal length greater than 300mm.

      Most lenses in this category are professional-quality lenses, which means they are built to be rugged and weatherproof. They are also VERY heavy and usually come with their own carrying cases.

      Having a bright viewfinder image is vital when you’re working in challenging conditions, particularly where light levels may be low and subjects are flighty. The faster   the lens the easier it is to focus.

      Factor in the additional cost of a sturdy monopod or tripod if you’re considering one of these lenses. Even lenses with optical stabilisation built-in can use some assistance in many situations.

      Canon’s ‘super telephoto’ prime lens range is targeted at sports and wildlife photographers and covers focal lengths from 200mm to 800mm. Nikon’s range goes from 200mm to 600mm, while Pentax has 200mm and 300mm primes and Sony has a 300mm f/2.8 prime. Olympus offers a 300mm f/2.8 Super Telephoto lens that is also compatible with Panasonic’s G-series cameras as well as a 150mm f/2 telephoto lens.

      Among the third-party lens manufacturers, Sigma offers 300mm, 500mm and 800mm lenses with mounts for the leading DSLR brands. Tamron’s longest prime lens is its 300mm f/2.8 LD [IF] lens.  


      Angled view of the EF 200-400mm f/4L IS USM Extender 1.4X lens. (Source: Canon.)

      Prime Lenses for Other Applications

      Architectural photography is another genre where specialist prime lenses can provide a quantifiable advantage. Regardless of whether the subject is interiors or exteriors, a tilt/shift (or perspective correction) lens will enable you to minimise   the distortions that occur when photographing buildings with wide-angle lenses.  



       Nikon’s 45mm tilt/shift lens showing the adjustments available for changing the alignment of the lens plane to the image plane.

      Tilt/shift lenses have adjustment screws that can change the alignment of the lens plane to the image plane (’tilt’) and move the lens elements parallel to the image plane (‘shift). The tilt control is used to control the plane of focus for a number of purposes:

      1. to enable objects at different distances from the camera to be sharply focused;
      2. to deliver a very narrow plane of focus (‘selective focusing’), leaving objects in front of and behind it very unsharp;

      The shift control is used  to keep the image plane and focus parallel to the subject and can be applied:

      1. when photographing a tall building to keep sides of the building parallel with the edges of the frame;
      2. in interior photography to avoid having the camera and photographer reflected in a mirror or by a reflective surface.

      One useful characteristic of tilt/shift lenses is their flatness of field, which also makes them good copying lenses. They can also be used to minimise parallax errors when shooting panorama sequences and composites using several rows of overlapping shots.

      Canon and Nikon each include a couple of tilt/shift lenses in their ranges. details can be found on each manufacturer’s website.

      Landscape purists often settle on a prime lens as their main lens for the genre. The most popular focal length is 35mm on a 36 x 24mm sensor or 24mm for a camera with an APS-C sensor. This focal length will provide a wide enough angle of view to encompass a typical scene without adding noticeable distortion.

      This is an excerpt from Photo Review Issue 48.

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