Wednesday, 26 December 2012

Lumix X 12-35mm f/2.8 sharpness evaluation

The Lumix X 12-35mm f/2.8 is the new premium standard zoom lens from Panasonic. It was launched before the Panasonic GH3 camera, but obviously intended as the kit lens for their highest quality cameras. With a steep price tag to boot, there is much anticipation to the image quality from this lens.


A viewpoint commonly found in online discussions is that a prime lens is always better than a zoom lens. With this in mind, it is sensible to compare this zoom lens with some prime lenses. I chose to compare it with the Lumix G 14mm f/2.5 pancake lens and the Sigma 30mm f/2.8 EX DN, which are both covered by the zoom range of the Lumix X 12-35mm lens.

At 14mm


Using a tripod, and with the GH3 camera at the base ISO 200, I took the same picture with both lenses. The focus distance was very short, about 30cm/one foot. The pictures are out of camera (OOC) JPEGs. I made sure to focus on the same item in both images, the lone branch in the upper left corner.

Lumix G 12-35mm @ 14mm f/2.8Lumix G 14mm @ f/2.5

Now, let me be the first to admit that there are many problems with this test setup. For example, the lenses have different lengths, so that the field of view turns out to be different in the two cases, even though the camera is at exactly the same place in both examples.

Also, since I am focusing on an item close to the border of the frame, what is in focus could be quite different in the centre of the frame, due to different focal plane curvature. However, despite these shortcomings, I think we will be able to see examples of items that are in focus in both pictures, and, hence, be able to do some comparison of their relative sharpness.

Here are some enlargements (100% crops) from the top left corner, where I set the focus point.


And from the top middle:


Finally, from the centre:


Based on these images, keeping in mind that the focal plane may be slightly different in the two last crops, I think we can conclude that they are pretty much equally sharp.

The Lumix X 12-35mm zoom lens appears to give a bit nicer bokeh, but on the other hand, the Lumix G 14mm f/2.5 handles the flare better. These observations are perhaps not surprising: We already know that the pancake lenses are not optimal in terms of bokeh. And when it comes to flare, we would normally expect that the simpler lens, with fewer lens elements, handles flare the best. The Lumix G 14mm pancake lens has only six lens elements, while the zoom lens has a whopping 14 lens elements. Flare is usually caused by unwanted stray reflection and refraction between the lens elements.

I think we can conclude that both lenses perform very well here.

At 30mm


This time, I focused in the single leaf in the centre of the frame. The focus distance was about one meter (three feet), suitable for a portrait photo.



Lumix G 12-35mm @ 30mm f/2.8Sigma 30mm @ f/2.8

While I thought that I focused on a single leaf in the centre, it turns out that they were two different leaves, at some distance, and the Sigma lens focused on the left leaf, while the Lumix lens focused on the right leaf.This just shows that extreme caution must be taken when doing these studies. Still, I think the 100% crops from the centre are interesting:


We see that both lenses are very sharp in the centre. We also see that the Sigma 30mm lens is more resistant to flare, again probably because of the simpler construction using only seven lens elements.

Here are some crops from the lower left side, to look at the bokeh:


Based on these examples, the bokeh looks just fine for both lenses.

Conclusion


My experience so far indicates that the Lumix X 12-35mm f/2.8 zoom lens has very good optical properties. I plan to make more comparisons later.

Despite using "nano surface coatings", the lens is prone to flare, though, but it is not unexpected for a lens of this class.

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