The picture below shows the lens at 45mm (left), and extended at 200mm.
The lens is somewhat longer than the Lumix G HD 14-140, to the left in the picture below, and a little bit slimmer.
The autofocus is fast and virtually inaudible. On the other hand, the aperture can be somewhat noisy, compared with the Lumix G HD 14-140mm superzoom, which is almost completely silent. The noise of the aperture can be compared with the Lumix G 20mm f/1.7 pancake.
When zooming, the focus is usually lost, meaning that you need to refocus, e.g., by halfpressing the shutter. This also applies when zooming during video recording. The focus is lost for a while, before the autofocus can regain the correct focus. This can be avoided by zooming very slowly.
The lens feels well built. It has the usual steel mount, and the extending lens tube does not wobble when zoomed to the maximum tele. Operating the zoom ring, it feels reassuringly solid. However, it does not have the dampened feel you would associate with a pro lens.
At the front, there is a 52mm filter thread, and you can use a supplied hood with bayonet mount. The lens features internal autofocus, and so does not change length when focusing.
Some uses for the lens
The focal length starts at 45mm, which corresponds to 90mm for traditional film cameras. This is the traditional portrait lens focal length. However, with f/4 as the maximum aperture at 45mm, the lens can hardly be called a true portrait zoom. With an aperture of f/4, you need to make sure that the background is fairly smooth to avoid having it stand out too much from the subject.
Still, I think that this lens is a good alternative for portraits on a budget. The aperture at 45mm is better than the original kit lens, which is limited to f/5.6.
The focal length is also good for sports and wildlife photography, however, with a somewhat limiting maximum aperture range, you will not be able to use the lens for these purposes when the light is dull.
Here is an example picture taken with the lens at f=61mm, f/4.1, 1/160 s, ISO 100:
Due to the limited aperture, the background is not very blurred, and stands out quite a bit.
The bokeh of this zoom lens is quite nice. I would say it's surprisingly good for such a lens. Here is a comparison with the Leica Lumix DG Macro-Elmarit 45mm and the Panasonic Lumix G HD 14-140mm
The lens is not as sharp as the Lumix G HD 14-140mm superzoom. However, it can hardly be expected to be that sharp, considering the price difference. The 45-200mm is sharp enough for most uses in the shorter end, but in the longer end you will benefit from stopping down the aperture a bit, if possible, for the best results. At 200mm, you may need to use a tripod to be able to stop down the aperture. Otherwise, the shutter speed will usually become too slow for handholding the lens at f/8, even with optical image stabilization.
There has been some uncertainty as to the sharpness of this lens at f=200mm, full tele. To evaluate this, I have taken one picture with a high shutter speed, on tripod, and with shutter delay to avoid triggering a camera shake when pushing the shutter release button. I also turned off Mega O.I.S. The camera was Panasonic GH1.
Here is the full image, scaled down to 1000x750 pixels. It was sharpened a bit:
To better evaluate the sharpness, I'm providing centre and corner 100% crops from the picture. The 100% crops are not sharpened. You can click on the picture to see the full resolution image.
Here is a 100% centre crop for f/5.6, 1/1600 second, ISO 400:
And f/7.1, 1/1000 second, ISO 400:
And corner crops with the same parameters. First f/5.6:
And at f/7.1:
Compared with the Lumix G HD 14-140mm f/4-5.8
Do you need the Lumix G 45-200mm if you already have the Lumix G HD 14-140mm? The difference between the maximum tele values is not that significant. 200mm is 42% more than 140mm, but the difference in field of view is not very large.
On the other hand, the Lumix G 45-200mm does give a significantly larger aperture through their common range. Both start at f/4.0, however, the 14-140mm very quickly goes to f/5.8, while the 45-200mm is more linear. The following diagram illustrates this.
As this diagram illustrates, the tele zoom Lumix G 45-200mm has an edge when it comes to providing better aperture than the Lumix G HD 14-140mm. On the other hand, the 45-200mm, while having a larger aperture, is not always sharp enough at the maximum aperture anyway, meaning that you will often want to close down the aperture a bit.
Compared with the Lumix G 100-300mm f/4-5.6
Should you get the Lumix G 45-200mm f/4-5.6 or the Lumix G 100-300mm f/4-5.6? This is largely a question about your intended usage of the lens. The Panasonic Lumix G 45-200mm tele zoom starts at a typical portrait focal length, and extends to a long tele. This is a very versatile focal length range for everyday photography, given that you complement with at least one shorter lens. You could walk around with the 45-200mm lens attached to your camera, and find that it suits most subjects well, except when you want to photograph a wide landscape, cityscape, a group of people, and so on.
The Panasonic Lumix G 100-300mm tele zoom lens, on the other hand, starts at 200mm (film camera equivalent), which is already a long tele lens. Then it extends to 600mm (again at 35mm film equivalence). This essentially means that the lens is a specialized tele zoom, and not well suited for everyday photography.
If you intend to photograph sports, wildlife, or events where you are situated far from the action, then you could consider getting the 100-300mm lens. But otherwise, I think the 45-200mm lens will be more useful for most people.
So my advice is this: If unsure, get the 45-200mm lens. Then you can learn what tele photography is about, and, if you want, complement with the longer 100-300mm lens later. After all, the 45-200mm lens is reasonably inexpensive, and gives a good value for money.
Compared with the Lumix X PZ 45-175mm f/4-5.6
A newer lens with similar specifications was launched in 2011. I have compared the two lenses here. In a nutshell, the newer lens is smaller, lighter, focuses slightly faster, and with the power zoom, it is better suited for video use. It is also slightly sharper optically, in my opinion. To get all this, you need to pay a premium price. The older Lumix G 45-200mm f/4-5.6 remains a value tele zoom lens.
As a macro lens
This is not a macro lens, but like many other tele zooms, it can be used to take pictures at small items. At 200mm zoom, the minimum focus distance is around 1 meter, which gives a magnification of around 1:5. This means that you can take a picture of something with a diagonal of 5 times that of the sensor, corresponding to around 90mm x 68mm.
You are limited to using apertures at f/5.6 or larger at 200mm. This is hardly an issue with macro images, since you will usually want to close the aperture down to at least f/5.6 to get sufficient depth of focus. One drawback is that this lens is not very sharp at 200mm. So to get the best image quality, you may want to close the aperture down to f/8.
Here is an example image taken at 200mm, 1 meter focus distance, f/5.6, ISO 800, and 1/5 second shutter, GH1. The camera was leaned towards a fence for some support to avoid excessive camera shake.
Another example image, this one taken with f=189mm, f/5.6, ISO 400, GH1. The camera was handheld at 1/320 second. The image was rescaled and sharpened.
Here is an example video capture done with the GH1
Another video shot using the Lumix G 45-200mm lens on a GH2: