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Sony 18-250mm DT Lens

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Last Update: 31 August 2010

One of the major benefits of the DSLR format is the ability to change lenses to suit the environment or subject matter to be tackled. There are occasions when it is more preferrable to just have one lens to tackle a range of subjects or just wanting to travel with the minimal amount of equipment. The Sony 18-250mm 3.5-6.3 DT lens has been designed with this purpose in mind. Its focal range is sufficient to capture wide landscapes through to zooming into distant subjects to pick out the details. The superzoom has become increasingly popular and 14x optical zoom maybe all some photographers will ever need.

The DT 18-250mm f/3.5-6.3 lens has the following features:

• 14x zoom with an effective range of 27-375mm
• Lens optimised for APC-S image sensors
• Light and compact body
• Lens lock

The lens is an all plastic build apart from the lens mount. The zoom ring occupies almost half the length of the lens with the focus ring being placed at the front of the lens and having half the wide of the zoom ring.

To protect against zoom creep the lens has a lock. The lens is essentially a rebadged revision of the Tamron 18-250mm but with upgraded AF mechnanics for faster focusing and Sony optics.

There is no image stabilisation built into the lens. As with all Sony lenses (and prior Konica Minolta) the image stabilisation is provided by the systems build into the Sony camera bodies. This method does not always make the lens cheaper or smaller than similar lenses with built-in stabilisation but it does mean that any compatible lens attached to an Alpha camera body will automatically benefit from the cameras image stabilisation feature. As always when needs be the tripod can always be resorted to.

The DT 18-250mm lens does not have in body AF system like SSM or SAM technology and so is reliant on the in body motor of the DSLR it is attached to for the autofocusing. Autofocusing is generally smooth across its range. The focus ring does not rotate during autofocusing.

The lens proved to be a bit noisy during autofocusing due to the mechanism in the lens. Focusing speed was dependant on the DSLR body used. It was responsive on the a700 but felt a bit slow at times on the a100. During manual focus the focus ring felt well damped but did not feel smooth in its action but it did its job. 

The zoom ring with its wide width was easy to grip. The zoom worked very smoothly and there was no sign of zoom creep at either extremes of the zoom range.

The lens aperture value increases with the focal length as follows:

• 18mm (27mm) : f/3.5

• 24mm (36mm) : f/4

• 35mm (53mm) : f/4.5

• 55mm (83mm) : f/5

• 75mm (113mm) : f/5.6

• 150mm (225mm) : f/6.3

As can be seen, whilst zooming the lens with the aperture fully open f/6.3 is reached well before 250mm. This can impact on the performance of AF as the phase (or contrast) detection systems have less light to work with.

The 18-250mm DT lens performed well in terms of sharpness. Results were generally sharp up to around 200mm after which there was obvious softening of images. Some improvement could be made by stopping down the aperture although there are limitations regarding how much this can be done due to the effects of diffaction.

Chromatic Aberration was present at the edges of images and seemed especially apparent at the telephoto end.

The Plus Points

• Sharp results up to around 200mm

• Good level of contrast

• No significant issues with flare

• Reasonably fast focus

• Zoom lock (although not found necessary)

• Build quality

The Negative Points

• Barrel distortion at the wide end

• Manual focus not so smooth

• Drop in sharpness towards extreme telephoto

It is very hard to critise this lens. The results were very pleasing as the lens performed extremely well for a lens of this design. Usually a number of compromises limit any possibility of serious use of a superzoom lens. The Sony 18-250mm is a definite advancement on what has gone before. The extreme telephoto end is the weakest aspect of the lens and the relatively slow optical speed of f/6.3 but it is most likely this focal length will not be used all the time. It happily fits the bill as a general purpose lens or as a travel photography lens where travelling light is a necessity. EA

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