First of all, it has slightly worse technical specifications: The long end of the zoom is 42mm, while the old had 45mm. Next, the new kit lens has got a plastic mount, while the older has a metal mount. The new zoom also lost the OIS switch: Switching OIS on or off is now done through the menus.
In terms of ergonomy, the new lens also lost the rubber zoom ring. It now features a plastic zoom ring, which gives somewhat less friction when operating it with your fingers. Some users of the old lens experienced that the rubber zoom ring came loose. This will not be a problem with the new lens, since there is no rubber ring.
Now, the change of the long end focal length doesn't bother me. 42mm and 45mm is basically the same field of view, there is no significant difference here. Also, the plastic mount, if done properly with good quality materials, is probably solid enough. After all, this is a very light weight lens, and in normal use, it doesn't need as strong support as larger lenses.
What about other aspects? Some reports indicate that the sharpness of the new lens is not as good as the original Lumix G 14-45mm lens. I cannot comment this, since I haven't used both.
Here's an analysis of the sharpness and bokeh of the lens.
The GH1 kit lens, the Lumix G HD 14-140mm, is specified with an aperture range from f/4 to f/5.8. However, while zooming from wide to tele, it closes down very quickly. So it is fair to say that this is essentially an "around f/5.6" lens, with a bonus brightness in the short end.
What about the other kit lenses? This diagram shows the relationship between the focal length and the maximum aperture for the three kit lenses:
For the 14-42mm and 14-140mm kit lenses, these values were sampled by using the actual lens. For the 14-45mm lens, I took the values from various reviews off the Internet.
It looks like the new kit lens has slightly better speed at f=25mm: f/4.6, compared with f/4.9 for the old kit lens.
I also added the aperture data for the premium Olympus standard zoom, the Olympus M.Zuiko Digital ED 12-50mm F3.5-6.3 EZ power zoom. This lens is comparable with the other kit lenses in the short end, but the aperture closes down very quickly as the focal length increases. I think this is consistent with the Olympus M 4/3 design philosophy, which generally puts compactness ahead of maximum aperture.
The main purpose of the kit lens, is to be cheap and good enough for most beginners. I'm guessing that the size and number of the glass lens elements is an important contributor to the price.
The diameter of the front element of the 14-42mm lens is 13% smaller than that of the 14-45mm lens. And that means the area is 25% smaller:
It is quite remarkable that Panasonic has essentially retained the specifications, while shrinking the front element so much. Of course, reducing the front lens diameter is not necessarily good for the image quality. It could lead to more vignetting at max aperture, for example.
All in all, I think this will be a pretty successful lens. Some early reports indicate slightly worse sharpness, however, for the target audience that may not be a problem. The cheaper construction means that Panasonic can sell them in kits at a lower price point, which they will need now that the competition has gotten their systems launched.
The autofocus speed of the newer 14-42mm lens is very good.
