Lumix 20mm compared with Sigma 30mm

A lot of people have complained that the Panasonic Lumix 20mm f/1.7 pancake lens is overpriced. To have a look at this statement, let's compare it with a lens in the same price range, the Sigma 30mm f/1.4.

The lenses have a lot in common. They share the same price tag in my market, and they do essentially the same job. The Lumix 20mm lens has a slightly wider field of view, and the Sigma 30mm has half a stop larger aperture. But these differences are not very significant. When I compare their fields of view, I refer to the Sigma 30mm being used on an APS-C camera, for which is was designed.

Here they are both:

The Sigma 30mm lens is shown with the supplied lens hood, which is very nicely designed. Sadly, the Lumix 20mm does not come with a hood, but I have put a step down ring on it, which acts as a compact hood.

As is apparent from the image, these lenses are very different in size. The Sigma (left) is 77x59mm, 430g. To the right, the Lumix is 25.5x63mm, 100g. Adding the supplied hood to the Sigma lens will make the difference even larger, of course.

When mounting the lenses to cameras, they look like this:

To the left is the Panasonic Lumix GH1 with the Lumix 20mm lens, and to the right is the Pentax K10D with the Sigma 30mm lens.

Image quality

What about the image quality? I tried to take the same picture with both setups, to see how they compare.

GH1 + Lumix 20mm @ f/1.7, 1/60 second, ISO 100 (click for larger image)

K10D + Sigma 30mm @ f/1.7, 1/45 second, ISO 100 (click for larger image)

Note that I used the same aperture on both lenses. The Sigma lens was stopped down from f/1.4 to f/1.7 to be comparable with the Lumix 20mm, which was used at the maximum aperture.

What we see straight away, is that the Lumix provides a wider field of view. I also think that the Pentax colours are more pleasing straight from the camera. Of course, using the RAW files you are free to adjust the colours of either images as you want.

To make the images easier to compare, I also added 100% crops from two sections of the images (click for larger image):

Here it is quite apparent that the Lumix lens is the sharpest. Also, there are less purple fringing artifacts in the Lumix image.

Now, we know that Chromatic Apperation (CA) artifacts are corrected for in software in the Panasonic Lumix G-series cameras. So the Lumix lens has an advantage here, in that these artifacts are automatically removed. Still, as a user of the systems, I care about the end result, not how it was achieved. And the end result is most certainly a lot better using the Lumix lens.

The Pentax setup uses phase detection autofocus (PDAF). With a large aperture lens like the Sigma 30mm f/1.4, this means that you can worry about the precision of the autofocus. Some camera body/lens combinations suffer from front-focus or back-focus. The setup might need expensive calibration to avoid these problems and achieve the best focus.

With the GH1 and Lumix 20mm lens, though, you get contrast detection autofocus (CDAF). With this system, you are ensured the best focus every time, as long as you set the focus region to suit your needs.

Size

The Lumix lens is a lot smaller and lighter. For me personally, that is a huge advantage. It could be a disadvantage for some users, though. Some customers might not take you seriously if you show up at a photography job with a small lens like this. When they pay for a photographer's services, some expect to get a person with a big camera and lens. For most users, though, this is not an issue.

Conclusion

From my point of view, these lenses, which do more or less the same job and are priced similarly, do not have an equal value. I much prefer the Lumix 20mm lens, which gives me better images, and is easier to lug around. I like the hood supplied with the Sigma 30mm lens. And having the option of using half a stop larger aperture is nice. However, you're not very likely to use the Sigma 30mm lens at f/1.4, since it is not very sharp wide open.

One could argue that my example image is not the most relevant for this type of lenses. These lenses are made for low light images of people, in which the corner sharpness doesn't matter too much. Also, while I haven't studied it carefully, I have a feeling that the bokeh from the Sigma 30mm lens is better. The Lumix 20mm bokeh is certainly very adequate, though.

I have also tested the autofocus of these two camera/lens combinations. The Pentax/Sigma combination is pretty fast in terms of autofocus, but not as fast as the Lumix. Also, the Pentax/Sigma makes much more noise when focusing.