It is only natural that the Panasonic Lumix 14-140mm zoom lens is associated with the Panasonic Lumix GH1 camera: They were both only available as a kit for the first months following the launch in spring 2009. It was only after some time that the lens could be bought alone. From January 2010, the GH1 can be purchased as body only in the UK.The lens has a 10x zoom ratio, and falls into the superzoom category. As is common for lenses of this type, it has a wide angle 28mm starting point (in 35mm camera equivalent terms), and goes all the way up to 280mm, which can be considered as a long telephoto lens.
This long zoom range comes at the cost of an aperture range which is not as impressive: f/4 at the wide angle, and f/5.8 at the long end.
One of the benefits of the Micro Four Thirds system is the compact size, and this benefit seems to be negated by the size of this lens. Even attaching it to the Panasonic GF1, the smallest M43 camera at the time of writing, gives a rather large and bulky package.
Since writing this, the lens has been superseded by the Lumix G HD 14-140mm f/3.5-5.6, which is smaller, lighter, and better in almost any way. I would certainly recommend that you consider the newer lens over the old one.
Aperture range
When looking at the aperture range of zoom lenses, it is common to observe the apertures of the end points. The aperture range, however, is far from linear. It increases faster than you might expect. The diagram below illustrates the aperture at various focal lengths (at 35mm camera equivalent) for the Lumix 14-140mm (blue) and the Nikon 18-200mm (red). As you can see, the Lumix lens has the smallest aperture range of the two, which we already knew, but in addition, the aperture closes down faster as the focal range increases, compared with the Nikon lens.
The 14-140mm lens has been criticized of being overly expensive, compared with similar lenses on the market. For example, the AF-S Zoom-Nikkor ED 18-200mm f/3.5-5.6G IF DX VR, with an 11% longer zoom range, half a stop larger aperture in the wide end, and is less expensive. Canon has also got a lens with the same specifications as the Nikon, and at an even more attractive price point.
Some answers to these comments have been that the 14-140mm has some unique features not found on other lenses: It is optimized for video recording, and features low noise fast autofocus, and an aperture that can change almost steplessly (at 1/6 stop intervals), and almost inaudibly. The aperture is also marketed as being very precise. Another advantage compared with the Nikon and Canon lenses is that it is more compact, at about 15% shorter at the wide angle setting.
Bokeh
I have compared the bokeh of the lens with the Lumix 20mm f/1.7 pancake lens, with the 45mm f/2.8 macro and the 45-200mm f/4-5.6 zoom lenses and the Lumix 14mm f/2.5 lens. It is fair to say that the bokeh of the 14-140mm superzoom lens is not the best. It is a bit "dirty" and features some ringing. However, with the limited maximum aperture, you're not likely to see much out of focus rendering anyway, so this is not a problem. The 14-140mm zoom lens is also more prone to flare, probably due to the complicated construction featuring 17 lens elements in 13 groups.
Sharpness
When using this lens on the Lumix GH1 camera in auto mode, the camera will almost always choose the largest aperture. The exception is outdoors photography in generous sunshine at wide angle. It is good then, that the lens is pretty sharp from the fastest aperture over most of the zoom range. There is little need to stop down, unless you need a very sharp image.
The images are somewhat soft at full aperture in the telephoto focal lengths, though. However, there is seldom room for stopping down the aperture further when photographing at full tele extension, as the shutter speeds tend to be on the slower side already. If you're using a tripod, and are photographing non-moving subjects, you could benefit from using a somewhat smaller aperture.
Here is a sharpness comparison with four other lenses at 140mm. This lens does not perform the best here, and, generally, the newer Lumix G HD 14-140mm f/3.5-5.6 is better.
Here is an example image taken at full tele, 140mm. I used f/5.8, ISO 320, 1/200 second handheld. The picture features the author Erlend Loe.
Here is an example video recording, filmed handheld, at f=108mm (216mm film equivalent), 1/100 second shutter speed, f/5.8, ISO 400.
