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Design

The 50mm F1.4 is a member of Sigma's premium 'EX' lens line, and build quality feels genuinely excellent, at least on a par with any of the other 50mm F1.4s currently available. The lens mount is metal, and the body apparently constructed of high-quality plastics, with Sigma's familiar textured EX finish. The body design is unique in this class, and similar to Sigma's 30mm F1.4; the optical assembly is entirely enclosed within the outer lens barrel which includes the filter ring, and moves backwards and forwards as a unit by about 8mm for focusing. This means that the front element is quite deeply recessed at longer focus distances, offering a degree of shielding from stray light even when the hood is not mounted.

On the camera

There's no getting away from the fact that the Sigma is simply huge for a 50mm F1.4, even managing to look large on the chunky Canon EOS 5D body (above left), and positively dwarfing smaller cameras such as the EOS 450D (above right). Despite this it handles well, with the focusing ring well-positioned towards the front of the barrel, and falling naturally to hand.

Autofocus

This lens uses Sigma's 'HyperSonic Motor' (HSM) variant of ultrasonic focusing for fast, accurate and near-silent operation. The good news is that this will be provided for users of all lens mounts, and (for the first time on a 50mm lens) offers AF with Nikon's D40(x)/D60 bodies. Unfortunately it also means that users of older Pentax DSLRs which don't support SDM lenses will lose out, and only be able to focus manually; in other words, the lens is effectively of KAF-3 mount specification.

In real life use, our Canon-mount sample performed well, with AF positive and reasonably fast under all but the most difficult conditions, using a variety of bodies from the 450D to the 5D (although as always, it must be noted that focus speed and accuracy is dependent upon a number of variables, including the camera body used, subject contrast, and light levels). However focusing was noticeably slower than Canon's own EF 50mm F1.4 USM and EF 50mm F1.8 II lenses, so this is still an area in which Sigma can improve. Focus accuracy was generally impressive, although with a certain tendency towards slight front-focus at close distances and F1.4, especially with low-contrast subjects. The lens also shows some evidence of a slight focus shift to the rear on stopping down, which meant our sample focused correctly when set to F2.

Lens body elements

The lens will be available in mounts for all currently available DSLRs except Four Thirds (i.e. Canon, Nikon, Sony, Pentax, and Sigma); our sample here is in Canon EF fit.

A nice touch is the inclusion of a 9mm wide ribbed grip towards the rear of the barrel, to aid lens changing.
The filter thread is 77mm, which is vast for a 50mm F1.4, reflecting Sigma's design goal to minimize vignetting. It does not rotate on autofocus, which should be welcome for polariser users.

Unlike other 50mm F1.4s, the filter ring is on the lens barrel and separate from the optical assembly itself. This view also shows how deeply recessed the front element is within the barrel at infinity focus.
The 45mm/1.8" deep petal-type lens hood features moulded internal ribs to minimize the reflection of stray light into the lens, and reverses neatly for storage.

The hood fits to the front of the lens via a bayonet mount; for those who struggle with such things, Sigma has helpfully included arrows marked 'In' and 'Out' indicating the direction you need to turn it.
The focus ring is 13mm wide, does not rotate during autofocus, and the action is smooth and precise. It rotates 90 degrees clockwise from infinity to 0.45m (i.e. the 'right' way for Sony, Olympus and Canon users, but opposite to Pentax and Nikon lenses).

The angle of view noticeably decreases on focusing closer, as is inevitable with unit-focusing primes.
Canon users will find a conventionally placed switch on the side of the lens barrel to select between auto and manual focusing modes.

Because the lens uses a ring-type ultrasonic focus motor, all users will benefit from 'full-time' manual focus, with the ability to tweak the focus setting even when the lens is set to AF.
A distance scale is provided with markings in both feet and meters. Sigma have also included a depth of field scale, although the spacing of the markings means it rarely provides truly useful information. A little playing with depth of field equations also indicates that it's been calculated for the 35mm full frame format, so it won't be terribly useful for the majority of users (and could be downright misleading for some).

Reported aperture vs focal length

This lens allows an aperture range from F1.4 to F16 to be selected.

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