Camera Accessories

Canon's new EF-S 55-250mm f/4.0-5.6 IS is designed specifically for cameras with 'APS-C' sized sensors and combines light weight with a very low price tag for an optically-stabilised lens. On the EOS 400D and 40D cameras we used for our tests, its focal length range is equivalent to 88-400mm on a 35mm camera. It's a fairly slow lens - and this is apparent in the viewfinder when you're shooting.

Optical components consist of 12 elements arranged in 10 groups, with one ultra-low dispersion (UD) element in the front group to suppress secondary chromatic aberrations and minimise coloured fringing. The built-in optical image stabiliser claims to give up to four f-stops of shutter speed advantage. Super Spectra coatings control ghosting and flare by internal reflections.

Polycarbonate plastic has been used as the major construction material in the body of the lens to minimise weight cost-effectively. Canon claims only environmentally-friendly, lead-free glass is used in the construction of the lens - but makes no mention of possible plastic components (which can keep costs and weight down without compromising optical quality).  

Build quality is good for a plastic lens and moving parts are acceptably tight. However, some care will be required when changing lenses as the lens mount is also made of plastic and, though appearing quite solid, may be vulnerable to chipping and (eventually) wear.

Both focusing and zoom rings have textured rubber coatings to provide a secure grip. The ridges on the focusing ring are narrower than those on the zoom ring and may trap grit. The zoom ring, which is 4cm long, lies nearest to the camera.

Behind the rubberised section on the zoom ring is a narrow aluminium band with engraved settings marking the 55mm, 70mm, 100mm, 135mm, 200mm and 250mm positions. Behind this ring, the lens carries slider switches for AF/MF and Stabiliser on/off settings. A white dot provides a position indicator for fitting the lens on a camera.
Aperture settings range from f/4.0 to f/22 at the 55mm setting and f/5.6 to f/32 at 250mm. At 250mm, the maximum magnification is 0.31x, which does not come into the true 1:1 macro range. The closest focusing distance is 1.1 metres.

Neither a distance scale nor indicators for depth of field or infrared adjustment are provided. The lens is supplied with end caps but no lens hood. A lens hood (ET-60) and lens case (LP1019) are available as optional accessories.

Handling
In both size and weight, the 55-250mm lens is similar to the EF 55-200mm f/4.5-5.6 II lens (which can also be used with 36 x 24mm imagers).  The two lenses have similar optical constructions and identical close focusing points, although the 55-250mm lens is marginally slimmer and 80 grams heavier and its barrel extends about 8 mm further at full zoom extension.  In our user tests it was a good match of the EOS 400D but felt slightly less comfortable on the heavier 40D body.

Moving from the 55mm position to the 250mm position required roughly a quarter of a turn and we found the markings on the lens barrel corresponded very well with the actual focal length settings.  When zooming from the 55m position to the 250mm position, the lens barrel extends by 62 mm and the front element rotates. This makes using angle-critical attachments like polarisers and graduated filters difficult. No zoom lock is provided - and none is required as the review lens showed no tendency to slide when carried pointing downwards.

The focusing ring also moves through about a quarter of a turn but is only usable when MF has been selected on the lens. Both focusing and zooming movements had a slight 'plastic-on-plastic' feel, although the movements themselves were relatively smooth.

Autofocusing speeds were good for a lens of this speed, even in low-light conditions. AF noise was relatively low. We observed a tendency to 'hunt' with low-contrast subjects, particularly in dim lighting and backlit situations.

Performance
The low price of this lens is reflected in some aspects of the optical performance of the review sample. Imatest showed it to be incapable of matching the performance of our test cameras' sensors.  Its lower resolution was evident in shots in a lack of  'crispness' around edges and an overall lower contrast throughout shots. These problems were evident with all types of subjects.

We obtained our best resolution figures for all focal lengths between f/6.3 and f/13 and resolution tailed off gradually as focal length increased. Some edge softening was detected by Imatest and apparent in many test shots.  On the basis of our tests, we would not recommend shooting with apertures smaller than f/14 with any lens setting. The graph below plots the centre and edge resolution from our Imatest tests against lens aperture and focal length.

Lateral chromatic aberration was generally low, as can be seen in the graph below, which plots the CA values against the focal length setting, with a red line marking the border between 'insignificant' and 'low'. We found traces of coloured fringing in shots taken at the longer focal lengths, although they could only be observed when files were enlarged to 100%.

Vignetting (edge darkening) was noticeable at the widest apertures and became particularly obvious at the 250mm setting. However, stopping down by two to four stops effectively subdued most of the effect. We found a fair amount of barrel distortion at the 55mm setting, which changed to slight pincushioning at around 100mm.  Flare was reasonably well handled and bokeh (out-of-focus blur) was good for a lens of this type.

SAMPLE IMAGES

55mm setting at f/16, 1/80 second, ISO 100.

250mm setting at f/16, 1/200 second at ISO 200.

250mm setting at f/5.6, 1/50 second at ISO  800. This shot shows the effectiveness of the image stabiliser and the bokeh of the lens at wide apertures.

250mm at f/9.0, 1/30 second at ISO 100. Another shot showing the effectiveness of the image stabiliser.

A platypus photographed just after sunrise. 250mm at f/5.6, 1/160 second at ISO 800.

250mm at f/8, 1/100 second at ISO 100.

100mm at f/18, 1/320 second at ISO 100.

250mm at f/7.1, 1/500 second at ISO 400.

70mm at f/5.6, 1/125 second at ISO 200.

55mm at f/6.3, 1/160 second at ISO 400.

Picture angle: 27 degrees 50 minutes to 6 degrees 15 minutes (diagonal at infinity)
Maximum aperture: f/4-5.6
Minimum aperture: f/22-32

Lens construction: 12 elements in 10 groups (includes one UD element)

Lens mount: Canon EF-S

Diaphragm Blades: 7 (rounded)
Minimum focus: 110 cm

Maximum magnification: 0.31x (at 250mm)
Filter size:  58mm
Dimensions (Diameter x L): 70 x 108mm
Weight: 390 grams