Telephoto prime or zoom?
The pros and cons of fixed vs flexible focal lengths
Prime super-telephoto lenses are favoured by wildlife pros, but you can get the same level of magnification from more affordable zooms. So what’s the difference?
Fixed focal length telephotos range wildly in terms of price and weight. Both aspects are largely determined by the lens’s maximum aperture: a 400mm f/5.6 is small, light and relatively cheap, while a 400mm f/2.8 is big, heavy beast – and expensive. But the f/2.8 aperture will suck in more light for faster shutter speeds and snappier autofocus, as well as giving you more control over depth of field. Prime lenses also tend to have more headroom when it comes to using teleconverters, in terms of both image quality and exposure.
Zooms give more flexibility, but tend to have slower ‘floating’ maximum apertures that get smaller as the focal length increases. That means the shutter speed gets slower as you zoom towards the subject – unless you’ve set Auto ISO which will adapt the exposure accordingly (see over the page). There are (pricey) exceptions, such as Canon’s 200-400mm f/4, pictured here.