Wednesday, December 24, 2014

Sony 18-105 f4 G OSS review



This is a user review of the Sony 18-105 f/4 (E PZ 18-105mm F4 G OSS Power Zoom Lens).  I will first discuss the rationale for getting this lens, then I will describe its physical characteristics.  I will then discuss its usage for photography, going over its optical characteristics and performance. Finally, I will briefly discuss its usage for video.

Unless otherwise stated, the photos here are from the Sony a6000 in raw, converted in Lightroom with the Huelight a6000 color profile, with no sharpening.


INTRODUCTION
The Sony 18-105 is a 5.8x walkaround zoom, but is unique in having a constant f/4 aperture.  Canon and Nikon have walkaround zooms with a constant f/4 aperture, but they are for full frame DSLRs (and therefore would not be wide enough on an APS-C body) and they have a narrower range.  As for mirrorless, at this time, there is no equivalent lens for any of the other mirrorless systems (MFT, Fuji, Nikon 1, Samsung, or even Canon EOS M) with a constant aperture. 

There are smaller cameras that could somewhat fill that need -- for example, the Olympus Stylus 1 (equivalent to 28-300mm focal length, constant f/2.8; reviewed here) which I also have, but I wanted a shallower depth of field and a higher image quality in low light conditions.  The Stylus 1 has a depth of field equivalent to a full frame aperture of f/13.1, whereas the 18-105's is equivalent to f/6.  I thought about getting a Sony RX10 (equivalent to 24-200mm focal length, constant f/2.8) but I instead got the 18-105, which was less expensive than an RX10 and moreover, when paired with the Sony a6000, has higher potential image quality (bit depth, color depth, noise) and shallower depth of field for the same field of view.



DESCRIPTION
The Sony 18-105 is a versatile 5.8x standard zoom with several features:
  • Equivalent to 27mm - 158mm.  At 27mm it's not ultrawide but it's wide enough to provide the distinct wide angle perspective.  At 158mm, it's long enough to provide a compressed perspective.
  • Unlike many other standard zooms for mirrorless cameras, it has a reasonably fast constant f/4 aperture. 
  • Optical SteadyShot (optical image stabilization).
  • Power zoom (you can zoom in and out either with the zoom ring or with a slide for smooth zooming in or out), which is very useful for videos.
  • Internal focus, which means the front element doesn't move.  Useful for polarizers or graduated filters.


From afar, the Sony 18-105 looks like a Zeiss lens, but it's not.  It is however, a "G" lens, which is Sony's designation for its higher-end lenses (not including Zeiss lenses).  The focus ring and zoom ring are electronic and have some damping so they move smoothly.

The body is mostly plastic.  The zoom ring and focus ring seem to be made of metal, as is the lens mount.



It comes with a reversible petal lens hood.  When the hood is reversed, the focus ring (which is the ring closer to the front element) is partially obstructed, though it is still possible to turn it.

with petal lens hood reversed

The Sony 18-105 f4 is one of the larger lenses in the E-mount lineup.  However, for its focal length and aperture, it's relatively compact.  It is 4.33 inches long and weighs 427 grams.  However, it has an internal zoom design, so the lens doesn't extend or retract when zooming.  By comparison, the Nikon 24-120 f/4 and Canon 24-105 f/4 (both full frame lenses) are 4.1 and 4.2 inches respectively but they extend when they zoom.

The 18-105 next to the Sony 50 1.8 and 35 1.8.
PERFORMANCE - PHOTO

Focal length
I found the 18-105 to be very useful.  I have about 10,000 shots on my a6000, and of those, around 4,900 are from the 18-105.  Granted, the numbers are skewed because I shot with bursts on the 18-105 (for sports) more often than I did with my other lenses.  Nonetheless, the 18-105 is one of my most often used lenses for the a6000 due to its versatility.


Having said that, we need to have realistic expectations about what this lens can do.  At its longest, 105mm (158mm full frame equivalent) is in the short telephoto range.  It is definitely long enough for photos of my family with most kinds of composition.  With sports, don't expect close up shots unless you're within hollering distance to the player.  Likewise with birds and wildlife.


Sharpness:  It helps to put this lens into context.  First, it's a zoom, and most zooms are less sharp than good quality primes.  Second, the specs are quite ambitious (5.8x zoom with constant f/4 aperture and image stabilization).  Third, the size is reasonable for the specs.  Fourth, the price is moderate.  If you combine all those design constraints for the 18-105, then one would expect the optical performance to be mediocre at best.

In fact, however, the sharpness is surprisingly good.  The 18-105 has excellent sharpness in the center at all focal lengths, even wide open.  Sharpness at edges depends on the focal length.  At its longest and widest focal lengths, the sharpness at edges is not great but is acceptable.  At middle focal lengths, the sharpness at edges is very good.

A good sport.
69mm f/4.0.  For middle focal lengths, the 18-105 has very good sharpness even off-center.
Here is a sample real world shot, at 18mm wide open, which is its weakest focal length:
18mm f/4.  This is the lens at its *least* sharp focal length, used wide open.
Here is another real world shot, at 105mm (also a weaker focal length), wide open.


And here is a 100% crop:
100% crop off-center.
Again, note that this is the lens at an optically weaker focal length.
If you are a pixel peeper or your photos need edge to edge sharpness, you will probably not be satisfied with the sharpness at the edges, or the sharpness of 100% crops at certain focal lengths.  For the rest of us, it looks sharp enough at any focal length.  



 
Distortion:  The 18-105 has crazy distortion, a compromise that was probably necessitated by the extreme design requirements.  The distortion is automatically corrected in realtime when viewing through the LCD or viewfinder, or when shooting video.  If you shoot in JPEG, you won't notice the distortion in your shots either because the camera will automatically correct for it.  If you shoot Raw and you use Lightroom, you will see the distortion but there's a lens profile that can also correct automatically for the distortion.  Fortunately, correcting for the distortion does not significantly diminish the sharpness.


Here is the shot before the correction was applied, showing the serious pincushion distortion:


Here is a 100% crop of the lower rightmost corner after correcting for distortion in Lightroom,with no noticeable impact on sharpness:


Chromatic aberration: The 18-105 has very good resistance to chromatic aberration.  For example, in the shot below, there are no CAs visible on the thin tree branches, and only very slight fringing on the bright water reflections.

no CA correction applied

100% crop. No CAs.

100% crop.  Very slight CA.  Not at all distracting.

100% crop.  CA corrected in Lightroom.

Flare:  It has strong flare resistance.  I haven't seen flare in a real life shot.  However, veiling glare (which reduces the contrast on the entire frame) is possible at certain angles to strong light sources.



Focus speed: The 18-105 focuses very quickly on the a6000.  It focuses fast enough to capture kids jumping around in a bounce house.  See this post.  Occasionally, however, my a6000 focuses on the wrong part of the scene (probably because I often rely on zone AF area).


The 18-105 focuses quickly enough to capture a child on a swing -- sideways, with no prefocusing. Image from JPEG
Depth of field, blur and bokeh:  At its maximum aperture, the 18-105 f4 has a depth of field equivalent to a full frame f/6 lens.  (By comparison, the RX10 has a depth of field equivalent to f/7.6 on full frame.)  At 105mm, the 18-105's physical aperture size (which directly correlates to its ability to blur backgrounds) is 26.25mm, which is almost the same as the 27.8mm physical aperture of the Sony 50 f/1.8 OSS lens.  The background blur (at their respective longest focal length and widest aperture) is similar.  However, their perspectives are quite different. At 50mm (75mm equivalent), the 50 1.8 is just slightly short for traditional portrait focal lengths.  At 105mm (158mm equivalent), the 18-105 is slightly long for traditional portrait focal lengths.  However, both can be used for portraits.

from JPEG

Speaking of blur, the quality of the bokeh is smooth and usually not distracting.  The exceptions are for long, thin objects in the background (e.g. branches), and for small spots of light, which can appear a little harsh (which is typical for many lenses).


The 18-105 has some difficulty rendering bokeh of small spots of light (including spots of light through leaves), which look like donut rings.

This is what the scene looked like - pretty much a worst case scenario for bokeh:

PERFORMANCE - VIDEO
I'm only a beginner when it comes to video but FWIW I have used the 18-105 to shoot my son's soccer games.  For video, the Sony 18-105 f4 is even more essential.  First, it has a power zoom.  That allows you to zoom more smoothly, and you'll also be less likely to jostle the camera, compared to moving the zoom ring.  The zoom lever also has a variable speed, and can be very slow (where you barely notice the zooming) or it can be at a moderately fast speed.  Alternatively, if you want to zoom quickly, you can use the zoom ring instead.


Second, because video has lower resolution than on a photograph (even for 1080p video) therefore, on the a6000, I can use up to 2x digital zoom to extend the effective focal length of the lens without degrading the image quality.  A digital zoom of up to 4x is available with some loss of image quality. When shooting video, you will be able to zoom past the 105mm limit, up to 2x (if Clear Image Zoom is enabled) or 4x (Digital Zoom enabled).  If shooting in raw or raw+jpeg, these options are grayed out and the zoom will be limited to 105mm in photo mode.  You can still use the extra zoom but only after you start shooting the video.  So, instead, when shooting video, I just switch to JPEG, which makes the extra zoom available before I start shooting with video (so I can frame my composition before shooting).

Third, the optical image stabilization is effective, and I can shoot at its maximum focal length handheld without any problems, although it has a hard time keeping the image steady when I'm walking (which is a torture test for image stabilization).  With the 2x zoom, it is still easy to keep the image steady.  With the  4x zoom, it is harder to keep the image steady though it is definitely doable as long as you're careful.

As for distortion, the a6000 corrects it in realtime and distortion becomes a non-issue.  Note: some Sony video camcorders such as the FS100 and FS700 don't correct the distortion, which makes the video nearly unusable for all but casual use.  I suggest checking to confirm if lens distortion in video is corrected in your camera.

Focusing in video is also very quick.  Occasionally, on my a6000, the continuous focus will lose the target or will not try to focus (possibly because the new subject is mistaken for a background).  When that happens, I just half-press the shutter, and the camera quickly focuses on the target again.
 
Here is a video (only 720p) with demos of the autofocus speed and image stabilization.  There is also a comparison between the optical and digital zoom.

from JPEG


CONCLUSION
The 18-105 f4 is a very versatile lens for candid and family photos.  It can capture anything from scene-setting shots to close-up portraits.  For videos, it is even more versatile (because of the extra reach of digital zoom).  The 18-105 is also unique in its class for having a constant f/4 aperture, a feature not found in other similar lenses except for full frame systems.

In terms of image quality, it is much better than expected for a moderately-priced 5.8x zoom.   But this lens is not for pixel peepers, or for people who need edge-to-edge sharpness. For those folks, I would recommend prime lenses instead.

It does have extreme distortion, but the distortion is practically a non-issue because it is corrected in realtime in the a6000 and correction does not seem to adversely affect the sharpness to a noticeable degree.  On the other hand, I don't know if all Sony cameras incorporate realtime correction, so I would double-check to confirm that your Sony body has lens correction for this lens.

If you're looking for a walkaround zoom for your E-mount camera, I would recommend this lens.  It's almost a must-have for candid and family photos, and is probably one of the best, if not the best lens for family videos.

For further info on the 18-105, also check out the ePhotozine review, which has Imatest resolution charts here.