Canon, Nikon, Sigma and Pentax non-zoom wide lenses go head to head

When does a 15mm lens have a wider field-of-view than a 14mm lens? One answer would rely on the 15mm being used on a full-frame body when the 14mm is confined to APS-C bodies. Alternatively, it might be because the 14mm is a rectilinear lens whereas the 15mm is a ‘fisheye’. Both of those answers appear in this review.

14mm lenses are important because they represent the limiting angle-of-view that can be achieved while keeping distortion to virtually zero. Lenses of this type use steeply curved front elements to create a flat (rectilinear) image field in which straight lines remain straight and there is minimal illumination fall-off towards the edges of the frame.

If the requirement to avoid distortion is relaxed then it immediately becomes possible to bend extreme off-axis rays even further to squeeze them into the picture frame. It is thanks to this relaxation that Sigma’s 15mm full-frame ‘fisheye’ delivers a wider field-of-view than Canon’s and Nikon’s full-frame rectilinear 14mm lenses, which in turn capture a wider field-of-view than Pentax’s rectilinear APS-C 14mm lens.

Cramming more into the frame is only one reason to use an ultra-wide lens: 
such lenses also offer the opportunity to capture extreme perspectives by getting close to the main subject while at the 
same time retaining an expansive background. All four of the lenses on 
test here invite both modes of use and deliver results that can be almost equally good in the right situations.
Nevertheless, it is the differences between these lenses that dominate in 
this test, and users who have particular requirements will quickly realise that their options are much more limited than might appear at first glance.

 

Image analysis





row 1, cell 1 row 1, cell 2 row 2, cell 1 row 2, cell 1
row 1, cell 1 row 1, cell 2 row 2, cell 1 row 2, cell
row 1, cell 1 row 1, cell 2 row 2, cell 1 row 2, cell

 

Nikon’s lens comes top in terms of MTF performance – though its advantage in this respect is relatively small, as the other lenses were close behind. MTF (Modulation Transfer Function) is an industry-standard method for measuring lens performance. A high MTF figure indicates that the lens can resolve more fine detail. The minimum figure for top-quality imaging is 0.25 cycles-per-pixel and the maximum theoretical figure is 0.50 cycles-per-pixel. Any lens that stays above the minimum figure across all (or most) of its aperture range is doing very well. The data for the graphs were obtained using Imatest software (www.imatest.com) and the graphs were created using RJS Office (www.rjsweb.net).  

Conclusion

The fact that three of these lenses are confined to single brands of camera bodies is almost irrelevant when their differences are thrown into the mix. For example, if you can afford nearly £2,000 for a lens, and you don’t use Canon, then buying a Canon body to carry the EF lens may not seem a bad idea. Similarly, the fact that Pentax’s lens offers only APS-C coverage is insignificant as all Pentax DSLRs use that format. Sigma’s lens is out on its own due to deliberate use of curvilinear distortion to achieve an unmatched 180° field-of-view across the entire full-frame field. Nikon’s provision of great retro-compatibility may not be enough compensation for the inability to apply manual changes with the lens in AF mode.

Only Pentax’s lens has an accessory thread that can be used to fit a protective filter on it. Canon’s and Nikon’s lenses have steeply domed front elements that are inadequately protected by their integral lens hoods; Sigma’s lens fares better but is still vulnerable. The only way to fit filters to the Canon, Nikon and Sigma lenses is to slot a specially-cut piece of dyed gelatine into the rear-mounted holder.

Potential buyers will wonder if an ultra-wide zoom might be the best choice. For users of APS-C systems, Sigma’s 10-22mm f/3.5 EX DC HSM is cheaper and scored more highly than these lenses. Pentax users would have to sacrifice one F stop of aperture with the zoom alternative. It is likely that the Canon and Nikon primes survive thanks to specific applications for which zooms are less suitable. For other users, nice though these 14mm lenses are, zooms may make more sense.