Some sharpness improvement is noticeable going from f2.8 to f5.6, but it's not a huge effect.Īgain the center was pretty good wide open, but stopping down to f5.6 showed a significant improvement. At longer focal lengths the CA was less visisble. This is the strongest CA I saw from this lens. As you can see, there is some chromatic aberration, but it's fairly well controlled and could easily be compensated for using an image editor such as Photoshop. The above samples are 100% crops from the left edge of the image. The image samples below are from the edge of the image. You can see it when you look carefully at the image at 100%, but on smaller prints you might not notice it. At the edge stopping down really doesn't make a lot of difference.
Stopping down improves center sharpness which peaks by around f8. Sigma 18-50mm f/2.8-4.5 SLD Aspherical DC OS HSM SpecificationsĪt the widest setting, 18mm, the overall sharpness is quite good, with the center being somewhat sharper than the edges. Sigma supply a lens hood with the lens and the warranty is for 4 years. The Sigma 18-50mm f2.8-4.5 SLD DC OS HSM uses three Aspherical elements to help minimize distortion and two SLD (Special Low Dispersion) elements to increase sharpness and lower chromatic aberration. This makes it about 2/3 stop faster across the whole zoom range than a lens like the Canon EF-S 18-55/3.5-5.6 IS. Maximum aperture is f2.8 at 18mm, f3.2 at 24mm, f3.5 at 28mm, f4 at 35mm and f4.5 at 50mm. It can be turned on and off via a slide switch on the barrel of the lens.
The Sigma 18-50mm f/2.8-4.5 SLD Aspherical DC OS HSM has one mode of optical stabilization which acts on both the horizontal and vertical axes.
#SIGMA 18 50MM F 2.8 MANUAL#
The lens does not have full time manual focus so to go from auto to manual it is necessary to slide the switch on the lens barrel from the AF position to MF. However the focus ring does spin during focusing and so you have to make sure not to hold onto it during AF. The Sigma 18-50mm f/2.8-4.5 SLD Aspherical DC OS HSM is both internal focusing and internal zooming which means that the lens length remains constant during both zooming and focusing and the front element dies not rotate. This is similar to Canon's USM and provides fast and silent autofocus.
Finally the HSM signifies that the Sigma 18-50mm f/2.8-4.5 SLD Aspherical DC OS HSM uses a hyper-sonic motor. The OS signifies the lens has internal optical stabilization (which Sigma claim can provide up to 4 stops of stabilization). It's a DC lens which means it's designed only for use on an APS-C sized crop sensor camera. Mounted on a Canon EOS body it provide a zoom range equivalent to that of a 27-80mm lens on a full frame camera. The Sigma 18-50mm f/2.8-4.5 SLD Aspherical DC OS HSM is Sigma's entry level normal zoom for crop sensor DSLRs. Sigma 18-50mm f/2.8-4.5 SLD Aspherical DC OS HSM Sigma 18-50mm f/2.8-4.5 SLD Aspherical DC OS HSM Review
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