see also:

• a catalogue of Micro Four Thirds lenses
• 3-5x standard range zoom lenses for Micro Four Thirds
• Panasonic 12-35mm f/2.8 X HD weatherproof lens
• Olympus ZD 14-35mm f/2.0 SWD lens
• Olympus announcement

Comparison of 3x zoom lenses on an Olympus OM-D E-M1 courtesy of 43Rrumours.com

• yet to be formally announced but strongly rumoured to come in Nov 2013
• a very useful 24-80mm field of view in 35mm full frame terms
• users should carefully consider the pros and cons of a zoom lens such as this excellent versatile lens or using 2 or 3 primes instead which will have better low light and shallower depth of field (DOF) capabilities such as the Olympus m.ZD 12mm f/2.0 lens, Olympus mZD 17mm f/1.8 lens, and Panasonic Leica DG Summilux 25mm f/1.4 ASPH lenses or Olympus m.ZD 45mm f/1.8 portrait lens
• that said, optical performance is comparable to these primes and for many this one lens could replace them for most purposes
• similar optical performance to the f/2.8 lenses for APS-C dSLRs and whilst you give up 1 stop shallow depth of field (DOF) capability, the lens is around half the weight which makes for far more portability, plus you get very fast CD-AF and it is almost waterproof, while filters are smaller and thus less expensive.

• MF clutch mechanism as with the Olympus m.ZD 12mm f/2.0 lens but with a neat new trick:
  • if you put the ring in the MF position, set your distance, then push it back to AF and focus, it remembers the MF position. This means you can pull focus instantly between any two distances simply by pulling the ring backwards! Better still, the distance is held regardless of the zoom setting.
  • this is very useful for focus pulling in video mode!
• image stabiliser is on the Olympus and the newer Panasonic cameras
• internal focus
• “ZERO” lens coating
• linear CD-AF motor
• MSC silent AF mechanism
• 7 circular diaphragm blades
• 62mm filter thread
• L-Fn button on lens
• close focus 0.20m from sensor plane
  • = 4cm working distance from front of lens giving maximum frame coverage is 48x36mm or 1:3 macro
• weatherproof
• 382g
• 84mm long
• similar MTF curves as the Olympus ZD 12-60mm but better at the edges at 40mm f/2.8 than the 12-60mm at 60mm at f/4

• see standard camera zoom lenses
• Canon EF-S 17-55mm f/2.8 IS USM for cropped sensor Canon dSLRs:
  • 27-88mm fov; twice as heavy at 645g; 111mm long; expensive 77mm filters;
  • IS is not as effective
  • more expensive lens but you do get 1 stop shallower depth of field (DOF)
  • optical performance is similar
  • much slower CD-AF
  • not as “waterproof”
• Sigma 17-60mm f/2.8 EX DC OS HSM for APS-C dSLRs:
  • 27-96mm fov on a Canon; almost twice as heavy at 565g; 92mm long; expensive 77mm filters;
  • aperture blades are not rounded
  • IS is not as effective
  • but you do get 1 stop shallower depth of field (DOF)
  • optical performance is similar
  • much slower CD-AF
  • not as “waterproof”
• Canon EF 24-70mm f/2.8L II:
  • no IS
  • close focus not as good
  • not as sharp in the edges?
  • more than twice the price and 2.5x as heavy at 805g, and a massive, expensive 82mm filter
  • much slower CD-AF
  • not as “waterproof”
  • but you do get 2 stops more shallow depth of field (DOF) - but if you really need this level of DOF control on Micro Four Thirds system, you can resort to fast aperture primes such as a 42mm f/1.2 which will give even more shallow DOF
  • this is the better lens for wedding photographers and outdoor fashion work but for most other uses, the Olympus lens will suffice, especially when complimented with a fast prime or two.
• Canon EF 24-105mm f/4L IS:
  • IS not quite as effective
  • not as sharp
  • more expensive
  • close focus not as good
  • almost twice as heavy at 640g
  • 77mm filter
  • not weather resistant
  • lots of distortion
  • much slower CD-AF
  • not as “waterproof”
  • but you do get 1 stop more DOF control

• Ming Thein's review
  • “Regardless of which camera you use, distortion is very, very well controlled indeed – there’s none visible at the long end, and just a tiny hint of pincushion at wide”
  • “some minor longitudinal CA on very high contrast subjects, but very little lateral CA in the plane of focus”
  • “Sharpness and microcontrast are excellent anywhere in the frame, at all apertures”
  • close focus performance is excellent in the center with just a little softening towards the edges making it a very useful close focus 1:3 macro lens.
  • “optically one of the best zoom lenses ever made”
• The Phoblographer.com
  • unusually nice bokeh for a zoom lens
  • What makes the lens so special is not only its excellent image quality which we can’t harp on enough, but the size, build quality, and speed in focusing.
• DxOMark lens test
  • similar optical quality to the Panasonic 12-35mm f/2.8 X HD weatherproof lens, Sigma 17-50mm f/2.8 and Canon EF-S 17-55mm f/2.8 lenses
  • moderate CA and distortion at 12mm (not as good as the Olympus m.ZD 12mm f/2.0 lens)
  • optically best at 25mm f/2.8, where edges are as sharp as Olympus mZD 25mm f/1.2 PRO lens at f/2.8 with similar vignetting and almost zero distortion, and better CA, but centre is a little sharper on the prime lens
  • sharpness falls off from 28-40mm (not as good as the Olympus m.ZD 45mm f/1.8 portrait lens)
• LensTip review
  • “The Panasonic G X VARIO 12–35 mm f/2.8 ASPH. P.O.I.S set the standards pretty high in this category but the Olympus company managed to meet them without any problem. First of all they produced a bit cheaper lens with a wider focal range. When it comes to the image sharpness the Panasonic is a bit more even but the Olympus provide a tad more lpmm at the maximum relative aperture. Apart from that you get slightly lower distortion and chromatic aberration, noticeably lower vignetting and distinctly better performance against bright light. The Panasonic, for a change, corrects the coma better and its off-focus images look nicer; it is also physically lighter and smaller, despite built-in image stabilization, and it is produced in Japan. ”
  • strangely, resolution drops wide open at 40mm so really need to shoot f/4 at 40mm.
• as good as this lens is, be careful not to drop it!
  • see user forum lens breaks due to plastic screw threads
  • however, this is likely to be a non-issue - see Lens Rental explanation of plastic lens mounts - they actually make lenses easier to repair
• ephotozine
  • superb sharpness across the frame wide open, which improves even further by stopping down to f/4
  • CA well controlled wide open, maximal at 12mm in the edges
  • vignetting 1.35EV wide open at 12mm, and 0.76EV at 40mm wide open; zero at f/5.6;
  • high levels (5.5%) barrel distortion at 12mm decreasing to 1% pincushion by 40mm
  • very resistant to flare
• Robin Wong
• http://www.fotozones.com/live/index.php/page/articles/_/reviews/review-olympus-12-40mm-f28-pro-r137
• http://leighmiller.zenfolio.com/blog/2014/12/olympus-m-zuiko-ed-40-150mm-f/2-8-pro-part-i
• http://www.lessgearmorephotos.com/olympus-12-40mm-f2-8-review/
• Olympus 12-40mm vs Canon 6D with Canon EF 17-40mm f/4 real world comparison
  • the Olympus has much better edge to edge image quality than the Canon 17-40mm in these tests