Sigma 18-250mm f/3.5-6.3 DC OS HSM
Tamron’s 18-250mm lens – later adopted by Sony – was so good that it really takes some effort to beat it. Sigma has put that effort in, but the cost is a very much larger and heavier lens. If all you got was some better performance, it might not be all that exciting. But you get potentially superior anti-shake through its built-in OS, and faster focusing with HSM, the Sigma equivalent of SSM. And you can buy it for under $430, and it works fine on the NEX A-mount adaptor for stabilised videos too – with some degree of autofocus tracking during filming.
So, here is the size difference. You can see the scruffy Sony rubber grip, but that brand new Sigma with even the a few days’ handling also picks up dirt. You are looking at a lens with a 72mm filter versus 62mm for the Sony, and it feels far bigger in the hand or on the camera. The zoom action is also pretty stiff if the lens is opposing gravity – trying to zoom in while tracking an aircraft or bird in the air above you needs a strong twist, as does zooming back if you are aiming down from a high viewpoint. However, the Sigma on the level has a good feel. I just wonder what time will do to the mechanism. Editor’s note, December 2010: after 18 months of use, it slips like any other zoom – aim downwards and you are at 250mm before you know it. These lenses need a lock which works at any z0om setting not just 18mm! Try shooting a small animal at ground level. Seems no maker has yet devised any zoom like this which stands up to a few months in use without becoming so sloppy it zooms itself.
The zoom lock only works at 18mm, as expected. It is positioned very close to the AF/MF switch which in turn is above the Optical Stabiliser on/off switch. With the camera to the eye, I sometimes operated either one of these when trying to hit the zoom lock release, most often the AF/MF switch.
Although the Sigma is HSM, do not confuse this HSM with the version found in the 70-200mm f/2.8 Sigma, or with Sony SSM. The focusing ring moves, to start with, and has no direct manual focus over-ride. To use manual focus you must switch the lens from AF to MF using the lens switch, not the switch on the camera body, or indeed the AF/MF toggle-hold button. All body controls for auto or manual focus are disabled and you can not turn the focus ring on the lens unless you switch to MF on the lens itself.
It is similar in operation to Sony SAM though the HSM motor is in a different class to whatever Sony has chosen put inside their SAM lenses. Focusing is moderate in speed for long travel (a typical HSM thing) but very fast indeed for tiny incremental adjustments. It is quiet as well. I would not swear that the Sigma is faster than the Sony with its mechanical drive, but it is much smoother in use. It certain gives the impression of being faster, and focusing is extremely accurate on our A700, A350 and A380 bodies alike. The focusing ring only needs about one-eighth of a turn from ‘beyond infinity’ to the closest (45cm, 18″) setting. The zoom ring uses a quarter turn and is well marked from 18 to 135mm with focal lengths 18, 24, 28, 35, 50, 80 and 135. Between 135 and 250mm there’s barely 15mm of scale and attempts to set a guessed focal length like 200mm could be wildly inaccurate.
Apertures appear to be f/3.5 until just under 24mm, f/4 from 24 to 35mm, f/4.5 to around 48mm, f/5 from 50mm to 75mm, f/5.6 from 80 to 135mm, and from then on f/6.3. These are not sudden jumps, of course, just the closest the camera can report to a continuous change in maximum aperture. This is a good result, especially at the wide end where having a true f/3.5 from 18mm to 23mm is unusual.
The lens itself comes with a petal hood, good quality front and rear caps, but no case. Why would you need one? This lens, if you buy it, will live on the camera all the time. The lens hood will reverse on to the lens, but should always be fitted properly for shooting. This complex zoom is no more flare-prone than any other, but it does have a very large front element which is not recessed.
When collapsed to 18mm, ideally locked to prevent zoom creep wearing the mechanism out prematurely, it’s a chunky but reasonably compact lens, comparable in size to the CZ 135mm f/1.8 or 24-70mm f/2.8 zooms for the Alpha system.
You can see here that even on the Alpha 700 body, not a compact design, the Sigma can also be an impressive weapon – perhaps attracting the wrong attention from security guards, community police, concert and sports venue staff or parents convinced you are the bogey-man or bogey-woman. Extended, it is as large as the Sigma 70-200mm (which does not change size). The double extension is very firm and not wobbly in the slightest – this is a well made lens, very solid with a metal mount.
Lens Construction – 18 Elements in 14 Groups
Angle if View (1.5X Format) – 78.5 – 6.5 degrees
Number of Diaphragm Blades – 7 Blades
Minimum Aperture – f/22 to f/40
Minimum Focusing Distance – 45cm
Maximum Magnification – 1:3.4
Filter Size – 72mm
Dimensions – Diameter 79mm x Length 101mm
Weight – 630g
SRP – £559.99