The Canon EF 24-105mm f3.5-5.6 IS STM is a general-purpose 4.4x zoom designed for full-frame DSLRs, although also compatible with cropped-frame APS-C models upon which it delivers a 38-168mm equivalent range. Announced in September 2014, it was Canon’s second full-frame EF lens with this range, following the EF 24-105mm f4L IS USM, and has since been joined by the Mark II version of that lens. Unlike those models, it’s not a member of the L-series and it lacks their constant f4 focal ratio, weather-sealing and USM focusing system. It does however employ Canon’s STM focusing which is smoother and quieter for live view and movie shooting, while also costing almost half the price of the EF 24-105mm f4L IS II USM.
The EF 24-105mm STM employs 17 elements in 13 groups and a variable focal ratio of f3.5-5.6 with a seven blade aperture system, and offers a four-stop optical stabiliser and a closest focusing distance of 40cm. The barrel measures 83mm in diameter, 104mm in length (when zoomed-out to 24mm), weighs 525g and employs a 77mm filter thread. In comparison, the EF 24-105mm f4L IS II USM employs 17 elements in 12 groups, a constant f4 focal ratio, 10 aperture blades, a closest focusing distance of 45cm, and measures 84mm in diameter, 118mm in length, weighs 795g, and employs a 77mm filter thread. So the STM version is a little shorter, but noticeably lighter.
The unique selling point of the EF 24-105mm STM is its focusing system: it becomes (and so far remains) the first full-frame EF zoom with Canon’s lead screw-type stepping motor, allowing it to focus quietly and smoothly in movies and live view. It’s also the only full-frame STM lens with image stabilisation and that’s wider than 40mm. These all make it the ideal walk-around companion for full-frame bodies with Dual Pixel CMOS AF, and in my tests it punches above its weight in terms of image quality. I miss the weather-sealing of the L models, but the optical quality for the relatively low price makes it a bargain in the Canon catalogue, and if you want an STM zoom for a full-frame body, it’s the only game in town at the time of writing.