I picked this lens up used for around £60 (pretty much as a laugh) so I had something small to go on my EOS M5. I wasn't expecting much, but this one turned out to be something of a pleasant surprise.
Pretty good. It seems to be mostly high-quality plastic with a metal mount. The assembly feels tight and refined, with pleasantly subdued styling. Its diameter is about 6cm, and with the front cap off and zoom retracted, it sticks 6cm out from the body, giving the M5 an overall length of about 11cm. Not quite pocketable, but getting there.
Focus and handling
On the EOS M5 focusing is instantaneous and precise: DPAF and STM seem well-matched. Manual focus is by-wire using a ring at the objective end of the lens, and must be enabled by an option in the body's software (as with disabling IS, since there are no switches on the lens itself). The lack of mechanical connectedness and slight latency can make this slightly twitchy, but not impossible.
The zoom ring is smooth to operate with a lattice pattern for grabbing rather than a rubber band. The lens retracts fully at 18mm, extending monotonically towards 55mm.
Nothing rotates during focus or zoom, allowing use of a (rather small) petal hood.
Optics and image quality
This is a variable aperture lens, and not the fastest. Such are the compromises associated with a lens of this size and market position. Pack a flash if it's dark, because as good as the image stabilisation is, there's often no substitute for more light.
Optically I can see nothing to complain about. Not super-outstanding-excellent -- there can be a bit of fringing, and at times the contrast lacks a bit -- but overall the resolution is well above satisfactory for an lens of this class with well-tempered behaviour across the frame. Chromatic aberration is moderate at the wide end (easily corrected in software), to pretty much non-existent by 55mm. I can see no obvious optical centering problems with this copy. Yes, stop the press:
CANON MADE A STANDARD ZOOM THAT ISN'T BADLY DECENTRED.
This scores big points with me. Every other wide-angle standard zoom I've bought in the past five years (from all three main vendors for the EF mount) has had some sort of visible alignment issue; scoring one that has only mild-to-no decentering (something more commonly termed 'just built correctly') is rare.
This image was taken at 18mm, f/5.6 on an EOS M5 at ISO 200. The image was processed from CR2 in RawTherapee with automatic CA correction, RL deconvolution sharpening, and no noise reduction. The triptych at the bottom shows 100% crops from the top-left corner, centre, and right edge respectively.
Next, 55mm, f/5.6 at ISO 160. Resolution falls off a bit, but not ruinously; this behaviour is reminiscent of its venerable peer the EF-S 18-55mm f/3.5-5.6 IS (the non-STM version).
Stopping down to f/7.1 sharpens things up a bit.
If one is content to work within its parameters and compromises, this is a wonderful little general purpose lens. It's worthy as both a gateway kit lens to show off the 24+ megapixel APS-C sensors in the EOS M lineup, and as a daily driver where size and/or weight is a consideration. Although I believe this lens is no longer produced, it is far, far better than its successor the EF-M 15-45mm f/3.5-6.3 (which is a daft milk bottle in comparison). Given the price the 18-55 tends to go for used, it is also excellent value.
Recommended -- every EOS M body owner should have one.