In full frame 35mm terms this lens is the equivalent to an 80-300mm f/2.8 range - the nearest equivalent in those terms would be the Sigma 120-300mm f/2.8 OS lens. Using an APS-C sensor size equivalence a 70-200mm f/2.8 (105-300mm equivalent).
Looked at in those terms, the lens is tiny by comparison. Weighing only 880g with the tripod ring attached or 760g without it is less than half the weight of a Nikon 70-200mm f/2.8 VR II lens and around a quarter of the weight of the Sigma 120-300mmf/2.8 OS.
The optical design features 5 ED (Extra Low Dispersion) elements, one SUper ED lens, One EDA (Extra Low dispersion aspherical) lens and one HR (High refractive index and dispersion) lens.
Just as with the Olympus 12-40 mm f/2.8, the lens is also equipped with a programmable function-button (L-Fn), with which you can choose pre-selected camera settings with "1 press of the button."
Compared to other Micro-4/3rds lenses, it dwarfs the tiny Olympus 40-150mm f4.5-5.6 R lens and is considerable larger than the Panasonic 35-100mm f/2.8 OIS lens.
Attached to the OM-D EM-1 or E-M5 the lens balances well and is easy to handle. Attach a battery trip to your OM-D and handling and balance improve still further.
As with the 12-40 pro lens, focus is instantaneous and instant manual override is available by just touching the manual focus ring (if set this way on your camera). The lens features the World's first Dual Voice Coil Motor (VCM) Focusing Mechanism, for super fast AutoFocus.
The built in 5-axis stabiliser on the OM-D E-M1 we used for testing does a fantastic job of keeping the viewfinder and taken image steady. Combining the fast f/2.8 aperture, great handling and excellent image stabiliser of the OM-D E-M1 makes this a dream to use for low light photography.
The range of focal lengths allows you to select areas in a scene or keep your distance and zoom in to your subject. The fast f/2.8 aperture combined with the rounded 9-blade aperture gives super smooth out of focus areas so your subject really stands out against even the fussiest of backgrounds.
The lens comes complete with a pouch case and a very clever sliding lens hood. The hood attaches to the lens and then slides back over the barrel for compact storage then a simple twist and pull and the hood locks in place giving excellent shading for the front element.
Regarding in to the light shooting, the Olympus 'Zero' lens coating provides outstanding resistance to flare so subject contrast is maintained in even the most difficult of lighting conditions.
Olympus also announced the availability of a 1.4x teleconverter for the 40-150 which gives you a micro 4/3rds range of 56-210mm or in full frame terms 112cm-420mm and reduces the maximum aperture by one f-stop to f/4. We have not had the chance to test the lens with the 1.4x but all reports so far are that lens quality and focus speed are maintained so this is a great add on and well worth having.
Park cameras are stocking the 40-150mm f/2.8 Pro lens alone or in a special money saving kit which includes the 1.4X.
So, to conclude, if you are looking for the very best telephoto performance and optical quality look no further than this lens - it is quite stunning! If you would prefer a more compact lens and are happy to only go to 100mm but want the f/2.8 aperture then the Panasonic 35-100mm f/2.8 is a great choice and if you want the 40-150mm range and are happy to accept an f4.5-5.6 aperture the Olynpus 40-150mm f4.5/5.6 lens is an absolute bargain.
For me, this lens is top of my wanted list and I cannot wait to get one and the 1.4x. After that the Olympus 7-14mm f/2.8 Pro lens and the 300mm f/4 Pro lens both due in 2015 I am sure will carry on the excellence shown by the 12-40 and 40-150.