Sigma 18-200mm f/3.5-6.3 DC AF OS Review
Sigma 18-200mm versatile F 3.5-6.3 DC OS lens has developed as a general-purpose lens for digital SLR cameras have been with ‘APS-C format’ image sensors. Offers a 11x zoom ratio and a minimum focusing distance of 45cm at all focal lengths, is this lens for photographers who want to be a single, long-range zoom lens to the camera body fit appeal. An integrated Hyper-Sonic Motor (HSM) uses ultrasonic waves that drive auto focus controls and provides fast and quiet AF.
SLD (Special Low Dispersion) and aspherical glass lens elements are integrated into the design to minimize a wide range of aberrations. be used consists of 18 elements in 13 groups, it has internal focus, which allows angle-critical filters (such as polarizers and graduates) without further adjustment in focal length settings changed. Petal-shaped lens hoods may also be present, although none has been delivered the review lens.
Like most lenses in its category, the Sigma 18-200 lens a seven-bladed iris, which opens to a wide circle of close openings to form. Maximum apertures range from 18mm f 3.5 to f 6.3 at 200mm in, while the minimum apertures are f 22 at 18mm focal length and f 40 at 200mm. These areas are in the extended zoom lenses and the f 6.3 setting provides plenty of room for different focus on 200mm usual.
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The lens is sturdily constructed, and we had no trouble fitting into the Canon EOS 400D and EOS 40D cameras we used for our tests. On the way to the back of the lens barrel is a broad, rubberized zoom ring that is ridged to provide a secure grip. A somewhat narrow focus ring in front of him. This ring is rubberized and has a stronger ridging.
A barrier stops behind the zoom ring on the lens or body, if it is running downwards. Behind and slightly below it is the AF MF switch and a little further down, the on off switch for the optical image stabilizer. Sigma OS (Optical Stabilizer) function uses two sensors inside the lens to detect vertical and horizontal movement of the camera, and you’re a dedicated group of lens elements to counteract camera shake.
The system claims to be able to automatically detect panning movement and normal camera shake. Closest focusing distance is 45cm supported throughout the zoom range, resulting in a maximum magnification of 1:3.9. A magnification scale displayed on the lens barrel, as it is extended with six settings from 1:3.9 to 1:12.8.
Performance
The overall performance has been extended for a zoom lens, good but not outstanding. Subjective assessment showed that most shots are quite sharp and detailed, although we have some color fringing on the edges of shots taken in bright conditions, found primarily on 18mm. Edge softening was also observed in these recordings. Both aberrations were only visible when images were enlarged and neither would interfere with normal photography.
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Imate tests showed overall resolution to slightly below expectations – although not unusual for a lens with such an offer extended zoom. Not surprisingly, the best focus at mid-range apertures was obtained. Imate also showed a steep decline in resolution at both ends of the aperture field with the attitude and 200mm at f 22 at 18mm focal length position.
Imate also showed lateral chromatic aberration, the low for most focal length and aperture, with a small slide into the lower end of the moderate range at the 18mm focal length. Some barrel distortion at 18 mm was also observed, but it was gone by 28mm and transferred to pincushioning at about 50mm. At no time either distortion was strong enough to affect normal shooting, even though both could affect architectural shots, especially with short camera-to-subject distances.
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Bokeh was pleased with wide lens apertures, especially at longer focal length settings. Flare was included in common – and obvious – in pictures with the lens pointed at the sun, though the sun was also shot dead. However, light was fairly well treated, when the front part of the lens was completely shaded.
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