Wednesday, 18 July 2012

Sigma 30mm f/2.8 EX DN Review: Not fast, not compact, but very good image quality

The Sigma 30mm f/2.8 is a somewhat odd lens. It is a prime lens which does not appear to have any of the advantages for prime lenses: It is not very fast in terms of maximum aperture, and it is not a small lens, compared with the pancake lenses that we have become used to. So why would anyone want to buy it? I'll get back to that question.

The picture below shows the lens together with the Lumix G 20mm f/1.7 pancake, which is both faster and smaller than the newer Sigma lens.


Physical

First of all, please note that the lens has changed appearance. What you see here is the first revision of the lens, which has an outer plastic shell, and ribbed plastic focus ring. In 2013, the lens received a cosmetic facelift, with a metal shell, and a smooth metal focus ring. Otherwise, the old and the new lenses are the same. So you can still use the optical tests here when considering the new version of the lens.

This lens rattles! If you buy this lens, and are worried about the rattle, don't be. It is normal. It appears to have something loose inside when it is not powered on. When in use on the camera, there is no rattle. Some people have speculated that the rattle is most probably due to the focus mechanism, which needs to be loose to achieve the quick focus speed.

Apart from the rattle, the lens appears very solid and well made. The focus ring is made of plastic, and is not rubberized. A rubber focus ring would have provided a better grip, but it works well with the plastic ring. It rotates smoothly.

The front lens element is surprisingly small. On the other hand, the rear lens element is very large, probably one of the largest I have seen on a Micro Four Thirds lens. It is also recessed quite a bit into the lens:


I'm guessing the recessed rear lens element is for compatibility with other formats. The lens has been launched also for the Sony NEX system (E mount). However, that system does not need a recessed rear lens element, since it has a shorter register distance than M4/3.

The Samsung NX, on the other hand, has a significantly longer register distance than M4/3, and my guess is that the optical design is made to be used on this system as well. Hence, on the Samsung NX system, this lens would be physically shorter, as more of the distance between the sensor and the rear lens element is taken up by the camera itself.

The lens looks quite a bit like the one on the Sigma DP2 Merrill compact large sensor camera. And perhaps it does use the same lens design.

Most other Micro Four Thirds lenses have an embossed red dot to guide you when mounting the lens to the camera. That is a good idea, since you can feel the dot with your fingers, making the mounting easy. The Sigma lens only has a white dot, which actually does make the process of mounting the lens slightly more awkward. This is not a big deal, for sure, but it is a detail to note.

Start up delay

Unlike all other Micro Four Thirds lenses I have used, this one does have a start up delay. Ok, so other lenses do jog the focus back and forth when powered on, but it just takes a fraction of a second, and is barely noticeable. This lens, however, does have a significant delay when powering on the camera, before you can take pictures. The lens does not appear to be doing much during this delay, but I guess it is calibrating the focus mechanism.

When powering on the camera, it takes three seconds before you can start taking pictures with this lens. Using the Lumix X PZ 14-42mm f/3.5-5.6 lens, which must physically extend before being ready, the startup delay is just two seconds.

But all in all, this is not any big issue.

No hood supplied in the box

This lens comes without any hood. And there are no means of connecting any hood, save for the 46mm lens threads. I decided to get a 46mm to 28mm step down ring, to screw into the front lens threads:


This provides some protection against stray light, and also against objects accidentally touching the front lens element. Having this basic hood attached makes me feel more safe when I use the lens.




Focus

The lens comes with a plastic focus ring, for manual focussing. The focus is "by wire", of course, like most other Micro Four Thirds lenses. Using the focus ring works fine, it rotates smoothly, and with a reasonable damping.

The autofocus is very fast, and virtually inaudible. I have tested the autofocus together with the Lumix G 20mm f/1.7 pancake lens and the Olympus 45mm f/1.8 portrait lens. The test was done indoor, at a reasonable light level (8 EV).

The focus distance was 0.3 meter for the shortest two lenses, and 0.5 meter for the Olympus 45mm lens, due to its longer minimum focus distance. I tested the autofocus by powering on the camera, and then triggering the shutter to see how long time it takes before the camera has changed the focus correctly. The lens is left in "around infinity" focus when powered on, so in this test, the autofocus moves from infinity down to near the minimum focus distance. Here are the results:



Lensfocus delay
Sigma 30mm f/2.80.44s
Lumix G 20mm f/1.70.60s
Olympus 45mm f/1.80.24s

As we see, the Olympus 45mm f/1.8 portrait lens has a very good focus speed. When considering that this lens has a large aperture, requiring more focus accuracy, this is especially impressive.

The Lumix G 20mm f/1.7 pancake lens has a traditional focus mechanism, pushing all the lens elements back and forth. This is known to be slow and noisy.

The Sigma 30mm f/2.8 has an internal focus mechanism, like most other Micro Four Thirds lenses, and is able to focus quickly and silently. Not quite as impressive as the Olympus 45mm, but still good. Be advised that most of the kit zoom lenses will focus faster, though. But I don't think that the focus speed is going to pose any problems with the Sigma 30mm f/2.8.

Portrait lens?

Traditionally, a portrait lens is a lens with a focal length of about 85mm or more, for the 135 film format. This corresponds to 42mm or more on Micro Four Thirds. The reason for this, is that with an 85mm equivalent focal length, you can take a headshot portrait filling the whole image frame at a distance of about 1 meter, sufficient to avoid any significant distortion of the facial characteristics. Going closer usually gives a chin and nose looking too large.

So can you use the Sigma 30mm f/2.8 as a portrait lens? It corresponds to 60mm on a traditional 135 film format, so in theory, it is too short for portraits.

However, I think that most people do not fill the face into the whole frame when taking portrait photographs. Rather, one usually leaves some space around the head. That allows you to use the Sigma 30mm lens at a distance of about one meter, sufficient to avoid distortions. I can illustrate this by photographing a natural sized head sculpture at 14mm, 30mm and 42mm. I used two lenses, the Lumix X PZ 14-42mm f/3.5-5.6 kit zoom lens, and the Sigma 30mm f/2.8:

Lumix X 14-42mmSigma 30mm f/2.8
Lumix 14mm f/3.5
Lumix 30mm f/5.3Sigma 30mm f/2.8
Lumix 42mm f/5.6

Sadly, the lightning changed when I took the last image in the series. Anyway, what we see here, is that when using 14mm, one must go very close to the face, giving distortions of the facial features. The nose and chin looks too large.

At 30mm, one can keep a distance of about 1 meter, which makes the face look natural. With the Sigma lens, one can use the f/2.8 maximum aperture, giving a nice blurring of the background. The Lumix kit zoom lens, on the other hand, the maximum aperture is f/5.3 at 30mm, which does not blur the background significantly.

At 42mm, the face looks pretty much like at 30mm, and there is little extra to gain in terms of naturalness.

My conclusion is that the Sigma 30mm f/2.8 lens can be used as a portrait lens, given that you stay around 0.8 meter or more from the subject. The f/2.8 aperture gives some background blur, and the bokeh looks fine.

The background does not blur away completely at f/2.8, so it is sensible to plan the photoshoot a bit, and avoid distracting objects behind the face.

Video use

The lack of image stabilization can be a problem with this lens, in terms of video use. It is hard to hold the camera stably at a fairly long focal length like this. On the Olympus OM-D E-M5 camera, you can use the internal sensor shift image stabilization during video recording, which I am told works fine. But on Panasonic cameras, and older Olympus cameras, there is no image stabilization at all during video recording.

In my experience, the autofocus works well during video recording on the Panasonic GH2, even in very low light situations. Here is one example video, recorded during a concert. The image parameters are: 1/25s, f/2.8, ISO 3200. The video was recorded at 1080p, 25fps, with the autofocus left on.



We see that the lens handles the high contrast situation very well, with little flare and loss of contrast.

Leaving the autofocus on during the video recording was no problem. This is unlike the Lumix G 20mm f/1.7 and Olympus 45mm f/1.8 lenses, which will often lose focus for some seconds during video recordings in dark settings like this, if you leave the autofocus on.

Image quality

I have tested the image quality by taking the same image with the Lumix X PZ 14-42mm f/3.5-5.6 kit zoom lens, and the Sigma 30mm f/2.8. All images were taken using a tripod, at base ISO for the GH2, 160. Here are the full images, with the focus set to the trees in the background:

Lumix 30mm f/5.4Sigma 30mm f/2.8

To better evaluate the image quality, here are some 100% crops from the images. Top right corner:


And from the centre of the image frame:


In the centre of the image frame, the image quality is very good straight from the maximum aperture for the Sigma 30mm f/2.8 lens. In the top right corner, the image quality improves a bit when stopping down to f/4, but is still very good from the largest aperture.

Bokeh

In this article, I have looked at the bokeh of the lens, compared with the Lumix G 20mm f/1.7 and Olympus 45mm f/1.8.

My conclusion is that the bokeh of the Sigma 30mm lens could have blurred the background is a more pleasing way: It can be a bit distracting in challenging lightning. But all in all, this is not a big deal, and for most uses, the bokeh is just fine.

Here is another study of the bokeh, with a comparison with similar lenses.

Close up performance

This lens has a minimum focus distance of 0.3m. In the Sigma online documentation, the maximum magnification is stated to be 1:8.1. This means that the smallest object you can photograph has a diagonal 8.1 times as large as the sensor diagonal, i.e., 14cm by 10.5cm. However, when testing this, I found that at the closest focus distance, I could photograph an object 12cm wide:


This works out to a maximum magnification rate of 1:6.9. I'm guessing that the quoted rate 1:8.1 on Sigma's homepage is for the Sony E mount version of the lens. On a Micro Four Thirds camera, the lens has a more narrow field of view, hence, the magnification rate is somewhat better.

This is not an impressive close up performance, but then again, this is not a dedicated macro lens in the first place.

The following image was taken at the closest focus distance using the Panasonic GH2 camera, at ISO 160, f/2.8 and 1/2000 second. I focused on the bumble bee:


The image is an out of camera jpeg, unprocessed beyond scaling it down to 1600x1200.

The purpose of this image was not to evaluate the sharpness of the lens. If so, it would have been better to stop down the lens to at least f/5.6, to get the bee and the flowers completely into the depth of focus. Rather, the purpose was to see how the lens renders the out of focus background at the maximum aperture, and the closest focus distance. I think the lens does well here, the background does not indicate any issues with the bokeh.

Here is another example image taken at the shortest focus distance, f/2.8:


Again, the bokeh looks just fine.

Software correction

Quite some Micro Four Thirds lenses need post processing in software to become give rectilinear images. The Sigma 30mm f/2.8 lens is designed to be rectilinear optically, though, and does not need any geometric distortion correction in post processing.

This will satisfy purists, those who feel that a lens should be perfectly optically corrected, and not require post processing to give rectilinear images.

New version of the lens

In 2013, this lens was discontinued, and replaced by a new lens called Sigma 30mm DN, and is part of Sigma's Art line of lenses.

The new lens has a new metal exterior, coming in silver and black finishes. However, the optical design remains the same. So the conclusions in this article still apply to the new lens.

The new lens is very similar to handle, with the exception of the smooth metal focus ring. The old lens had a ribbed plastic focus ring. Both work perfectly fine.



Conclusion

At first sight, this lens looks rather bland. It doesn't have a large aperture, nor any zoom. And the lens is not very compact, compared with the Lumix pancake lenses. On a Micro Four Thirds camera, with a 2x crop ratio, the lens corresponds to 60mm equivalent field of view, which is somewhat unusual.

So why would anybody want to buy this lens? First of all, it turns out to be a rather nice lens. It has good image quality, handles flare well, and the bokeh is good. Further, it focuses quickly, and is quite inexpensive and light. The autofocus works well during video, and is virtually inaudible. The lens has a matte and unobtrusive look, which adds to the usefulness as a portrait lens and street photo lens.

When the Olympus 45mm f/1.8 was launched, it closed a major gap in the lens lineup: The portrait prime lens. However, this is still a somewhat expensive lens, and it has a silver appearance that I think looks quite cheesey. The Sigma 30mm f/2.8 may be the first really cheap portrait lens for the Micro Four Thirds format. For a user who only has the kit zoom lens, this lens could be a cheap way to try out a prime lens.

While the Olympus 45mm f/1.8 is certainly the better portrait lens, it is a bit long for more general use. The Sigma 30mm f/2.8, on the other hand, is long enough for (most) portrait use, and short enough to be used as a "daily walk around lens".

When designing a lens, there are some factors that add to the complexity significantly, mainly:

  • A large aperture
  • A large zoom ratio
  • A very wide angle
  • A very small size

This lens has neither of these, which is one of the reasons why it is cheap in the first place.

However, there is a flip side to this: The optical design of the Sigma 30mm f/2.8 is not compromised by the complicating factors above, meaning that it has the potential of giving very good image quality. For the best image quality, you should, in theory, look for a lens which has a moderate focal length, moderate maximum aperture, no zoom, and no pancake design, just like the Sigma 30mm f/2.8.

I would recommend this lens to anyone who wants to try a portrait lens on a budget, or people who are interested in the best image quality at a low price.









3 comments:

  1. I'm very happy with this lens. The focal length suits me and the autofocus is impressive. The bokeh is not always pleasing, though - it seems to me that particularly contrasty backgrounds can get quite distracting.

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    Replies
    1. Yes, the focal length makes good sense. Long enough for portraits, and short enough for general use.

      Your comment about the bokeh is good, I should test this more thoroughly.

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    2. I think it'll be interesting, as I have only subjective feelings about it and you could be more thorough. From what I can say, the bokeh of close objects with few contrast (for example the leaves of a bunch of flowers) is pleasing, while that of far objects with higher contrast (for example a garden with sunny and shadowy parts) is not.

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