Friday, 10 October 2014

Normal lens shootout

Some decades ago, when film SLR cameras became popular, the 50mm lens was abundant. Due to the long register distance of SLR cameras, the 50mm lens was the shortest which could be designed cheaply with a large aperture, which is why it became so popular. It became the standard lens people bought with an SLR camera, the normal lens.

Nowadays, the kit zoom lens has become the normal lens, but the field of view corresponding to a traditional 50mm lens is still popular. So most manufacturers release a fast "normal lens" when they invest into a new lens mount. In this article, I will compare two normal lenses for two different systems, the Nikon 18.5mm f/1.8 for Nikon 1, and the Leica 25mm f/1.4 for Micro Four Thirds:

LensNikon 18.5mm f/1.8Leica 25mm f/1.4
AnnouncedSep 13th, 2012Jun 13th, 2011
System crop factor2.72
Equivalent focal length50mm50mm
Maximum aperturef/1.8f/1.4
Equivalent max aperture, in terms of DoFf/4.8f/2.8
Weight70g200g
Diameter56mm63mm
Length36mm55mm
Filter thread40.5mm46mm
Minimum focus0.20m0.30m
Lens elements/groups8/69/7
Hood includedNo, HB-N104Yes
Focus ringNoYes

Both correspond to 50mm field of view on a 135 film camera, and both are quite fast, with large maximum apertures:




Physical


Both lenses feature the now fashionable finish: A smooth and glossy barrel. However, the Nikon lens has a ribbed pattern on the front of the lens, which is not, as one could expect, the focus ring. Rather, the ribbed ring does not rotate, and makes it easy to get a good grip on the lens when mounting it.

The Lumix 25mm lens has a nice, rubberized focus ring, which rotates smoothly and is a joy to use. Both lenses feature internal focus, and appear very solid and sturdy.

From the rear side, we see that both lenses have an exit pupil recessed into the lens, which is covered by a matte, ribbed surface, as one would expect.


Both lenses have relatively large exit pupils relative to their formats. However, the exit pupil of the Nikon lens is of course smaller, since it covers a smaller sensor area, and it has a smaller maximum aperture.

The Nikkor 1 18.5mm does not come with a hood supplied, but you can buy the optional HB-N104 hood, pictured to the left below:


I think this Nikon hood is very nicely designed: It does not add any extra diameter, it offers a real protection against stray light, and it protects the front lens element against finger prints. Further, you can still use same front lens cap on the hood, as it has the same 40.5mm opening diameter. I would highly recommend getting the HB-N104 hood.

The Leica 25mm f/1.4 does come with a hood in the box, but I don't like it much. It is too wide for a normal lens, but not wide enough to be reversed around the lens barrel. I think the hood is designed to look retro, not to be functional, which I think is sad.

Autofocus


For still image photography, both lenses focus very quickly.

Here is a comparison of the continuous autofocus performance during video recording. I used 1080p 60FPS on both cameras, the Nikon 1 V3 and the Lumix GH4. I set the ISO to 200 on both cameras:



We see here that the Nikon system performs vastly better. I think this is not so much because of differences in the lenses, but rather because of differences in the cameras.

Nikon have successfully implemented on-sensor PDAF right from the start in the Nikon 1 cameras. This works very well both for AF-C with moving subjects, and for continuous AF during video recording, at least as long as the light is reasonably bright.

Panasonic have implemented the DFD (depth from defocus) technology on the Lumix GH4, which does improve the continuous autofocus compared with previous generations. But it still lags significantly behind the Nikon mirrorless technology in this aspect.

Image quality


To test the image quality, I have taken a number of pictures with both lenses. I used a tripod, and a 2 second shutter delay to avoid camera shake. I also set the base ISO, for the best quality. As for the cameras, I used the Nikon 1 V3 and the Lumix GH4 (my review):


Here is a test at near infinity focus distance (click for larger images):

Nikon 18.5mm @ f/1.8
Leica 25mm @ f/1.4

Here are 100% crops from the centre of the image, at various apertures:


And from the lower left corner:


Here we see that the Leica lens is remarkably sharp already wide open in the centre. The Nikon lens is not as sharp wide open, but sharpens up when stopped down to f/2.8

In the lower corner, which tends to be more challenging for all lenses, the Leica 25mm lens again does much better in terms of sharpness. Even if the Leica lens improves when stopping down, it is still very adequate wide open in the corner.

And here is a test at near portrait distance (click for larger images):

Nikon 18.5mm @ f/1.8
Leica 25mm @ f/1.4

In this collection of 100% crops from the centre area, we see that, again, the Leica lens is the most sharp:


But the big problem in this example is not the sharpness, the problem is the flare handling. The strong light source inside the image frame is handled well with the Leica 25mm lens, which still retains a good contrast level.

With the Nikon 18.5mm lens, though, the strong light source flares inside the lens, causing a loss of contrast, as well as a ghost image of the light source mirrored around the optical axis. Using the hood is not going to help here, as the strong light source is inside the image frame. This problem does not go away when stopping down the lens.

Finally, here is another test at a fairly distant focus. The focus was set on the digger in the foreground:

Nikon 18.5mm @ f/1.8
Leica 25mm @ f/1.4

These 100% crops from the top of the image tell the same story again: The Leica lens is the most sharp out of the two.


Bokeh


The nature of the out of focus rendering is called bokeh. For a large aperture lens, the bokeh is very important. If out of focus objects are rendered in a distracting way, then you cannot use the largest apertures anyway, which makes the lens less useful.

Here, I have focused on the metal tube, and we can compare the out of focus highlights in the background, click for larger images:



Leica 25mm @ f/1.4
Nikon 18.5mm @ f/1.8
Leica 25mm @ f/1.8
Nikon 18.5mm @ f/2.8
Leica 25mm @ f/2.8

As you see, the bokeh of both lenses is perfectly fine. I would say that the Nikon lens has the most round out of focus highlights when stopped down.

See another bokeh comparison here, featuring a number of large aperture lenses.

Geometric distortion correction


Most mirrorless lenses feature some in camera distortion correction. To examine the geometric distortion characteristics, I have photographed a square tiled wall, and then overlaid the out of camera JPEG (in black) with the uncorrected image (in red). I used the third party RAW converter software UFraw to assess the uncorrected image.


The percentage in brackets is the relative distortion correction applied in The Gimp image processing software to get a rectilinear image. This is a way to compare the relative distortion between the lenses.

Contrary to what many would have guessed, the Leica lens is the one which requires the most distortion correction in post processing. I don't see this as a problem, though. I think that designing lenses to require some geometric distortion correction is a sensible choice, and allows the lenses to be more compact, and give better end results.

Portrait lens?


These lenses have a large maximum aperture, typical also for portrait lenses. So, can you use them as portrait lenses?

Sort of.

With a 50mm equivalent focal length, you must go quite close to fill the face into the whole image frame. Typically, you need a distance of around 0.5m. At this close distance, you will get distortions to the facial features, i.e., the chine and nose looking very large.

To avoid this, use a longer lens for portraits, which allows you to take the same images from a distance of about 1m, safe from these distortions. Example lenses can be the Nikon 1 Nikkor 32mm f/1.2 for Nikon 1 cameras, or the Olympus 45mm f/1.8 (my review) or Leica 42.5mm f/1.2 for Micro Four Thirds cameras.

Read more about the subject here, including example images.

Example images


Nikon 18.5mm @ f/1.8
Leica 25mm @ f/1.4

Here are 100% crops from both images:


Conclusion


The simple conclusion here is: You get what you pay for. The Leica 25mm f/1.4 is the most expensive, but it is also by far the best lens.

The main advantage of the Nikon lens, is the size and weight: It is truly portable. Given the price, I would say it performs well. It is plenty sharp enough for most use, and the flare issue is not a problem with normal, low contrast, daytime use.

Pros: Compact, light, inexpensive, good bokeh.
Pros: Consistently good image quality, very good handling of high contrast, making it perfect for night images.
Cons: Not super sharp, poor flare performance.
Cons: Expensive, not very compact.

Alternative lenses, Nikon 1


Within the Nikon 1 ecosystem, there are not really any alternative lenses. While Nikon released the 18.5mm fast normal lens fairly soon, to the joy of enthusiasts, they have not since made any more lenses of this category, and it is not very likely that they will at this point.

The closest thing to an alternative is the Nikon 32mm f/1.2 portrait lens. While it is much longer, it shares the aspect of being fast, with a large maximum aperture.

Alternative lenses, Micro Four Thirds


The Micro Four Thirds system is more mature, and has an impressive lineup of lenses.

From Olympus, there is the Olympus 25mm f/1.8. Not as fast as the Leica 25mm f/1.4, but more compact, and cheaper. It is not a whole lot cheaper, though, so personally, I would rather spend a bit more and get the Leica 25mm f/1.4.

For those who like using manual focus lenses, there are the Cosina Voigtlander Nokton 25mm f/0.95 and the SLR Magic 25mm T/0.95. These are fairly large and expensive, though.

Further reading


A further test of the Leica 25mm lens, as well as some example night photos.

About the concept portrait lens.

9 comments:

  1. Great comparison review!

    I find the PanaLeica 25 f/1.4 quite a bit slower auto-focusing compared to the MZuiko 17 f/1.8 on my OMDEM10. Maybe its the other way round on a Panasonic body...? It rather sad though if Olympus and Panasonic gives disadvantage to each others lenses.

    ReplyDelete
  2. I don't think it is the other way around on Panasonic.
    From my experience (gf3 vs em10), panasonic autofocus works better with both olympus and panasonic lenses. My em 10 in comparison tends to struggle more in difficult situations.

    I think it is normal that the 25 f1.4 creates more often difficult situations than the 17 f1.8 due to the thinner depth of field.

    ReplyDelete
  3. LOL wow thats amazing the Panasonic 25mm f1.4 that costs 3x as much, weighs 3x as much is 60% longer ,when tested on the £1200 GH4 { which weighs 80% more } compared to the overpriced lol £700 V3 is a fraction "better"

    ReplyDelete
    Replies
    1. This is in fact quite common. The Nikon 18.5mm lens is already quite good, and to top this with a significant increase in the quality, you would normally need to pay a lot more.

      Delete
  4. Hi Fredrik,
    you went the same way as i.From m4/3 to Nikon One and back again.The quality of m4/3 is still better than Nikon One.But i like the Nikon One system because of compactness and design.I like to work with both systems.

    ReplyDelete
    Replies
    1. I don't expect to leave Micro Four Thirds, far from it. But Nikon 1 has some advantage, mainly compact, light, and well performing tele lenses, like the Nikon CX 70-300mm.

      For most other uses, M4/3 is still the better choice.

      Delete
  5. Did you notice that the Nikon "rattles",when the light changes?

    ReplyDelete
    Replies
    1. Are you thinking about the "rattlesnake" sounds that the Leica 25mm lens will make when in changing light?

      I haven't noticed that with the Nikon lens during my use so far.

      Delete
    2. Thank you for the quick answer, like always :-)
      I don`t know the Leica 25mm,but it seems to be similar.Btw,i remember that the Sigma 2,8/19 had the same "problem".

      Delete