Both of these lenses have somewhat odd focal length for the Micro Four Thirds format, compared with conventional prime lenses. The 19mm lens has the same field of view as a 38mm lens on a traditional film camera, while the 30mm lens corresponds to 60mm. Both of these focal length equivalents are unusual.
However, the answer to these odd focal lengths lie in the fact that the lenses were designed for the APS-C format. With a smaller crop factor of 1.5x, the lenses correspond to the 28mm and 45mm, i.e., the classic wide angle and normal lens, respectively.
Also, keep in mind that while 19mm is an odd focal length for Micro Four Thirds, it is very close to 20mm, and the Lumix G 20mm f/1.7 is a very successful lens. They are both shown below:
First of all, just like its sister lens the Sigma 30mm, this lens rattles. Something is loose inside the lens when it is not in use. This is a bit annoying, but no problem. Once the lens is connected to a camera, and the camera is turned on, the rattling stops.
Again, just like the Sigma 30mm, the rear lens element is recessed quite far into the lens mount:
Since the register distance of the Micro Four Thirds format (20mm) is fairly close to that of the Sony E-mount (18mm), this does not seem to be the explanation for the very recessed rear element. I'm guessing the explanation is that the lens was designed to be used also on the Samsung NX mount, which has a significantly longer register distance of 25.5mm. At this time Sigma has not released the lenses for Samsung NX, but perhaps they will in the future if the format takes off.
The exterior of the lens is black matte plastic, and it has a quite non-obtrusive look.
The focus ring is wide, and made out of ribbed plastic. It rotates smoothly, with a reasonable amount of dampening. The focus is of course "by wire", just like virtually all the other Micro Four Thirds lenses. There is no mechanical connection between the focus ring and the actual focus distance of the lens. And there is no focus scale.
There is a small start-up delay when powering on the camera, unlike most other lenses. The delay is around 1.5 seconds, shorter than for the Sigma 30mm lens.
The autofocus is fast and virtually inaudible. Here is an autofocus speed comparison with the Lumix 20mm f/1.7 pancake lens. As expected, the 19mm lens focuses much faster. There is also a big difference when using the lenses for video. Here is a side by side comparison with the 20mm lens, which shows much better performance when using the 19mm lens. Both lenses are set to f/2.8:
While the autofocus speed is not quite as fast as the modern zoom lenses, it is still more than fast enough, and should be no problem at all for normal use.
I made a sharpness comparison with the Lumix G 20mm lens. It shows that the 20mm lens is the best, no doubt about it. But the Sigma 19mm lens is still quite good.
Here is another sharpness test, compared with the Lumix X 12-35mm f/2.8. The full images at f/2.8 are here:
Sigma 19mm f/2.8
In terms of sharpness, the two lenses are fairly equal in the centre. However, in the corner, they are far apart. Here are 100% crops from the top left corner:
We see a quite clear difference. The Sigma 19mm lens suffers from some Chromatic Aberration artefacts (red and green fringing). While the colour fringing can be corrected in an image processing program, there is also some more general dullness. When stopping down, the performance improves some.
The Lumix G 20mm f/1.7 lens relies on in-camera geometric distortion correction. The Sigma 19mm f/2.8 does not. However, the output image is not 100% rectilinear, as you can see below.
This is not that unusual. In fact, the Lumix 20mm lens, even after the in-camera adjustment, features some residual barrel distortion. And when photographing people or nature, this is no issue at all, nobody will notice the barrel distortion. But if you use this lens to photograph cityscapes and architecture, you will surely find this problematic.
I compared the bokeh of the 19mm lens with that of the 20mm and 12-35mm lenses here. The 19mm lens has more pleasing bokeh than that of the Lumix G 20mm f/1.7.
Compared with the Sigma 30mm f/2.8
In my opinion, the Sigma 30mm f/2.8 EX DN lens is quite good considering the price. The 19mm lens does not shine quite as much, with more CA artefacts in the corners, and a lower level of sharpness. They both have nice bokeh and fast focus, though.
Compared with the Lumix G 20mm f/1.7
Make no mistake about it, the Lumix G 20mm f/1.7 is a better lens. It is sharper, faster (in terms of aperture), and much more compact. In terms of bokeh, though, I think the 19mm lens is better. The 19mm lens also focuses much faster, and less audibly. For video, I would use the 19mm lens, unless I really need the extra aperture, and can do without autofocus.
Lumix G 20mm f/1.7
Sigma 19mm f/2.8
|Front lens thread||46mm||46mm|
You may consider to buy the Sigma 19mm lens over the Lumix 20mm lens to save money, as there is a significant price difference. Or if you need a better autofocus performance during video. But for the best optical performance, the Lumix G 20mm f/1.7 is the better choice.
New version of the lens
This lens is in fact already discontinued. Replacing it is a new version of the lens, called Sigma 19mm F2.8 DN, and is part of Sigma's "Art" line of lenses. It has the same optical design, but a different exterior. The focus ring is now made out of smooth metal. The lens is available in silver metal finish, and in black finish:
From an ergonomic point of view, this is a strange choice. A smooth surface appears to be poor material for a focus ring. On the other hand, handling it feels surprisingly good. So I would say that this is no real issue. It looks like the remake is all about a new styling, and not any change to the optical properties.
Here is an example image to illustrate the out of focus rendering at close focus image, at full open, f/2.8. The focus was set to the rose in the lower left corner:
The bokeh is generally very nice, however, there is a bit of ringing in the top right corner.
Another example image, with a focus distance of about 3 meters, at f/3.2, 1/60s:
And here are some 100% crops, which illustrate the CA artefacts in the top left corner, and that the quality is good in the centre:
While the Sigma 30mm f/2.8 gave a good value for money in terms of optical performance, the Sigma 19mm can be seen as more lacking. And with the Lumix G 20mm f/1.7 outperforming the Sigma 19mm, it is hard to recommend the Sigma lens, unless you are on a tight budget, or if autofocus performance during video is important to you. The Sigma 19mm lens is not bad, far from it, it just doesn't reach up to the Lumix G 20mm lens, or the sister lens, the Sigma 30mm f/2.8.