|Exotic elements||3 ED||2 Asph, 2 ED|
Based on the specifications, it is easy to see that the newer lens looks more interesting. It is smaller, lighter, has more exotic lens elements. The only negative item is that it has a shorter zoom range. However, the difference between 200mm and 175mm maximum extension is barely significant.
In the specifications, it looks like the two lenses have the same aperture range. And they do have, f/4-f5.6. However, when looking at the aperture as a function of the focal length, it is easy to see that the new lens in fact has a less impressive maximum aperture for all focal lengths between the start and end-points:
This means that the new lens not only gives a slightly shorter zoom range, it is also a slower lens on average. However, I guess that lenses like this tend to be used in the very shortest and very longest settings the most, so this might not be big issue.
Physical, Power Zoom
The most striking difference between the lenses is of course the size and weight. Beyond that, the newer 45-175mm lens has the all-black "premium design", associated with the Leica branded lenses from Panasonic. The older 45-200mm lens has the "common design", featuring a grey ring around the base of the lens.
Another fundamental difference between the lenses is that the new lens has power zoom (PZ), and also internal zooming. Internal zooming means that the lens doesn't change shape during focal length change. The old lens, on the other hand, extends when zooming towards the long focal length range, which is very common for tele zoom lenses. Internal zooming makes the new lens feel very solid. There is no wobbling front section, unlike the older 45-200mm lens.
Power zoom is a feature mostly included for video use. Zooming smoothly manually during video recording is pretty much impossible. But with motorized zooming, it is possible to zoom while recording a video. On a personal note, I think that zooming during a video capture almost never looks good, and is best avoided. But at least the new lens makes it possible to do this with a better result.
For still image use, power zoom is not needed. And some would even argue it is a nuisance: You have better and more precise control with a manually operated zoom ring. However, I find the implementation of the motorized zooming to be very good. There is the option of zooming using a broad, rubberized ring, or using the switch on the side. Using the ring for zooming feels almost like using a mechanically coupled manual zoom ring. There are two exceptions: The zoom ring does not stop when reaching the end of the focal length range, and you cannot see the focal length by looking at the position of the ring. Rather, you must take a look at the display to see the actual focal length.
When using the zoom ring while recording a video, it has the advantage of smoothing out the zoom movement for you, so that the zoom action becomes more even. Using the zoom lever makes the zooming even more smooth. It is possible to operate the motorized zoom at different speeds using the zoom lever, by pushing it more or less hard. This works well
The rubber zoom ring feels a bit thicker and more generous than the old lens. Also, the focus ring feels a bit more dampened than the old lens.
I have tested the autofocus, and compared it with the older 45-200mm lens. I found the autofocus to operate a bit faster than the old lens. The old lens is also very fast focusing, so this is a good achievement.
As with other Contrast Detection Autofocus (CDAF) systems, the focus accuracy is very good. Unlike Phase Detection Autofocus (PDAF), calibration of the lenses and camera bodies is not needed. However, as with all other long lenses, you must take care that the camera focuses on what you want to have in focus. Even if the aperture is not very large in the long setting, f/5.6, the depth of focus (DoF) is still narrow enough that you may experience to focus on a background object rather than the subject. So make sure you understand how the autofocus modes work, and consider using centre spot mode to have full control over what comes in focus. This is important when using the lens in the longest tele zoom extension.
Autofocus while zooming
The older Lumix G 45-200mm f/4-5.6 lens is not optimal when it comes to keeping the focus when zooming. It is clearly not parfocal, and loses the focus immediately when zooming. The longer Lumix G 100-300mm f/4-5.6 (my review) is somewhat better in this respect, but still has this problem.
With the newer Lumix X 45-175mm lens, this is still a problem. When zooming during video recording, I've found that it can keep the focus fairly well if the background is static. However, with excessive subject movement or camera shake, the focus can wander off for an extended period of time. In general, you can not expect tack sharp focus until around one second after you stop zooming. This will take longer if the lens is zoomed in.
Here is an example showing how zooming while video recording can look using the two lenses:
As you can see, both lenses fail to focus perfectly while zooming. However, the newer lens generally does a bit better. Also, it is easier to zoom smoothly using the new lens. Especially when using the zoom lever. An added benefit is that keeping the camera stably is easier when using the motorized zoom through the lever.
I could find examples where the new Lumix X 45-175mm lens also fails to retain focus while zooming. This would typically happen if there is excessive camera shake, much subject movement, or very close distance. Closer distance is more challenging for the lens, especially at a long zoom.
When comparing the sharpness of the two lenses, it is hard to find much difference with low contrast test images. This can be seen here, in my first sharpness tests. However, with high contrast images, for example with back light, I've found the new lens to be consistently better. It has less Chromatic Aberration (CA) artefacts, and less flare.
I would say that the newer Lumix X 45-175mm lens is generally sharper wide open. When using a Panasonic camera in auto mode, it will almost always choose to use a long lens like this wide open, so the wide open performance is important.
Here is another sharpness comparison with four other lenses at 140mm. Again, the Lumix X 45-175mm lens comes out as one of the best performers.
The term bokeh denotes the rendering of out of focus areas, which can vary a lot between lenses. I have looked at the bokeh of the two lenses by using a high contrast night image as an example. The focus is set on the foreground, which is about 1m away. The focal length was 45mm in both cases. Here are the full images:
Lumix G 45-200mm
Lumix X 45-175mm
Looking at some 100% crops from the top right region reveals that the bokeh from the newer Lumix X 45-175mm is not optimal. The out of focus hightlights are rendered as non-round discs off the centre:
The problem of non-round out of focus renderings becomes smaller as the lens is stopped down. In low contrast situations, this is not an issue at all, since you wouldn't see the bokeh discs as clearly as here.
Optical Image Stabilization (OIS)
Just like almost all other zoom lenses from Panasonic, this lens features optical image stabilization (OIS). Based on my experience, this appears to be effective both during still image photography and video recording. It is almost impossible to video record stably at 45mm and longer focal length without a tripod, so OIS is pretty much needed for video.
In online forums, there has been much discussion about the effectiveness of the OIS with this lens. I cannot see how I can test this scientifically, and hence my advice is: If you are worried about the rumored dysfunction of the OIS, then don't buy the lens. My personal opinion is that this problem, if it is a problem, is way overrated in online forums.
Here is an example image taken at 45mm, f/4.0, ISO 160, 1/60s, OIS on, handheld:
And a crop from the centre of the image, not re-scaled or sharpened:
This image was taken at 175mm, f/5.6, ISO 320, 1/50s, OIS on, handheld, but with the camera supported against a railing:
And a crop from the middle of the image, not re-scaled or sharpened:
And this image was taken at 175mm, f/5.6, ISO 640, 1/125s, OIS on, handheld, but supporting my wrist on a hand rail:
And a crop from the top left part of the image, not re-scaled or sharpened:
This video was done with the GH3, using the Extended Tele Conversion (ETC) mode, and the zoom mostly around 100-175mm. The camera was handheld:
A video recorded using the GH2 at ISO 160, f/6.3 and mostly f=175mm. One of the wider shots was recorded at a shorter focal length.
The camera was hand held, but rested against a hand rail.
Another example video, recorded handheld with the GH2. The zoom was set to about 60mm.
I think the OIS system does a good job of keeping the image stable. Compare it with a video recorded using the Olympus M.Zuiko 45mm f/1.8 non-stabilized portrait lens. In the video recorded using the MZD45, I was not able to handhold the camera sufficiently stable.
After 1.5 years of extensive use, I accidentally dropped the lens on a hard wood floor from a height of 1.5 meters. The lens bounced a couple of times before coming to rest, and I thought that this lens is gone for sure. However, the only visible side effect from the accident is that some chrome has chipped off one of the mount flanges:
Beyond that, the lens works just as before, and continues to give very sharp and good images. This indicates that the lens is very well constructed, and can take a lot of abuse, should you be unlucky and drop it or bang it into something.
The newer Lumix X 45-175mm lens is a good improvement over the existing Lumix G 45-200mm lens. It is better optically, and much more compact and light. It also feels more solid, without any extending section when zooming. The power zoom (PZ) implementation is well done, and works fine also for still image use.
While some of the specifications are better than the old lens, it should be noted that some are also worse. The new lens has a slightly shorter zoom range, and is about 1/3 stop slower in the middle of the zoom range. Out of focus renderings of highlights are non-round outside of the centre of the frame. This is mostly a problem only for night time photos. The bokeh is quite good in daylight situations, when the contrast is lower.
So which lens should you buy? If you are interested in video use, then I think it makes sense to get the newer Lumix X 45-175mm lens, since it generally gives you better footage, and allows for smooth zooming while filming. The new lens could also give better image quality for stills use. All in all, I think it comes down to how much you want to spend, and how much you value the compactness. Both lenses are certainly good.