Sony 20mm f/1.8G Lens Review

bythom sony20mmg.jpg

What is It?

Sony has been rounding out their lens lineup in admirable fashion. The f/1.8 line of primes now consists of:

  • 14mm f/1.8GM (that review)
  • 20mm f/1.8G (this review)
  • 35mm f/1.8
  • 50mm f/1.8
  • 85mm f/1.8
  • 135mm f/1.8GM

We also have 24mm, 35mm, and 85mm f/1.4GM and 50mm f/1.2GM lenses to help round up the fast prime lineup. Some gaps might still said to exist (16mm, 18mm, 28mm, and 105mm), but overall it's unlikely that you can't find a solid basic set of three or more lenses that cover what you need covered. Most folk use fast primes to supplement their zoom set (whether f/2.8 or f/4), and we now have fast Sony primes that live in the wide-angle zoom, mid-range zoom, and even telephoto zoom range. Bravo. 

As usual with the high-end lenses we have a fair deal of complexity in the optical formula (for a prime): 14 elements in 12 groups. We've also got two advanced aspherical and three ED elements. About a third of the glass in the lens is "special" in some way. Nano AR coating is also used in this lens, and the front element is fluorine coated for dust and water resistance. Sony's engineers are doing a lot of light ray manipulation in this design. 

Up front we have a 67mm filter ring. A bayonet-type lens hood is included (ALC-SH162). 

Size is surprisingly small, at just 3.3" (84.7mm) in length and 3" (73.5mm) in diameter. The lens is also surprisingly light for its specification, at 13.2 ounces (373g). I'm not aware of any equivalent 20mm lenses that are smaller and lighter.

The left side of the lens (holding the camera) has one function button appropriately positioned for the left hand, and one switch that can move the lens from AF to manual focus operation.

The aperture ring is capable of being both clicked or de-clicked, controlled by a switch on the right side of the lens (as you're holding the camera). Third stop settings are clearly marked from f/1.8 to f/22, plus there's an A position for when you want to use body controls for aperture setting. The physical aperture is controlled by a 9-blade aperture diaphragm. 

The focus ring is out front and easily found by touch, though it isn't as wide as some of Sony's focus rings. The ring is the usual fly-by-wire focus one you find in the E/FE mount. No focus marketings or DOF markings are present. Close focus distance is about 8" (0.20m). Sony is using dual linear motors to focus the lens, and focusing is internal (no lens extension).

The lens is sealed for dust and moisture resistance, ala all the G and GM lenses.

Price of the lens is US$899, and is made in China. 

Source of the reviewed lens: purchased

Sony’s Web page for the lens

How's it Handle?

As usual with primes, there's not a lot to write about. The fly-by-wire focus ring is smooth, as you'd expect, and much more dependent upon how the camera is set than anything about how the lens functions, at least in terms of performance and accuracy.

The aperture ring has very stiff third stop points when set to clicked. It's physical difficult to move out of the A position, which is good. De-clicked the ring is smooth, but it will make sound as you turn it (a faint scratching type sound typical of mechanical rings). 

The lens handles well on the A7 bodies, though there is a "clunk" sound that happens when you tilt the unit when it's powered off (likely from declutching the focus elements). 

How's it Perform?

Sharpness: The best attribute of the lens, with a slight catch. 

In the center, this lens is simply excellent, and I'd probably say superb. That's true wide open, it's true at any aperture until diffraction starts taking away acuity. The catch is the extreme corners. No, they're not up to the level I'd like them to be, though they're still what I'd call good- wide open, and maybe even very good at the best aperture, which is f/4. 

The problem is that the center is so good that the corners definitely will show "fall off". By contrast, the Nikkor 20mm f/1.8 S is just a tiny bit less sharp in the center but better in the corners than the Sony, and that makes for a substantive difference in my book, particularly if you're doing real estate, architectural, or cityscape photography. Astigmatism and coma are reasonably well corrected, so at least the corners just "soften" instead of smearing. Still, I'd personally rather see a bit more balance across the frame than the Sony lens shows. Of course, at the price of this lens, I'm asking for a lot. 

Some of this corner issue is a bit of field curvature, which is common with a lens this wide. Thus, you can mitigate that by carefully choosing your focus plane and depth of field, but with "flat" subjects (e.g. architectural) you can't always do that. Like the 14mm, the field curvature seems to be mostly in the nearer focus distances than overall.

bythom visual sony20mm.jpg

Dark green = excellent, Medium green = very good to excellent-, light blue/green = good to very good-. The wider the darker green areas stretch, the better the lens is corner to corner.

Chromatic aberration: Both corrected and uncorrected the lens seems pretty well behaved in lateral chromatic aberration. Even on the 61mp A7R Mark IV I wasn't seeing much pixel-wide problems. Even longitudinal CA seems reasonably well under control, with only minimal purple/green shift.

Vignetting: Probably the worst attribute of the lens, as I measure about 3 stops of corner darkening without correction, and even stopping down doesn't really pull this down to a level I'd call acceptable. Which means we're stuck with Sony's corrections. My advice? Don't use them, as they encode into the raw file in a way that will cause you problems later. Moreover, Sony's corrections aren't exactly full to start with. I still measure a bit more than one-and-a-half stops vignetting wide open.

Linear Distortion: Surprising for a mild wide angle lens, the 20mm f/1.8G has a very mild mustache distortion pattern to it . The lens corrections do a fine job of negating that. Note that uncorrected, there's clear barrel distortion in the APS-C frame limits (above 1%), while the edges straighten.

Flare: Green ghosts can appear with sun in or just out of frame. Not as bad as some Sony wide angle lenses I've seen, but it's definitely something you'll want to watch for. I did see a few faint red/magenta ghosts in extreme situations, but that was rare. Overall, I'd characterize the flare tendencies of this lens as "good" for a wide angle lens, but not great. 

Bokeh: Mostly nice. A little bit of a bright rim, but no coloration. No obnoxious onion skinning, though if you look really close you'll see patterns in the out of focus areas that are low-level onion skin. Stopped down even a bit I see some irregular aperture issues: the top and right side of "the circle" has a pronounced set of visible diaphragm joints. Cats eye is low, though when stopped down the circles do become elliptical.

Final Words

Well, it's a G lens. If you were hoping for a GM lens, note the missing M ;~). That actually sums things up fairly well: this is a very good to great lens, but not an exceptionally great lens. Sony made some compromises (vignetting, edge acuity compared to center) to produce the lens at the price they gave it. Build quality is high but not the highest. Optical performance is high but not the highest. 

I'm not sure I'd be using it at f/1.8, so some of the weaknesses of the lens are basically negligible to me. As a landscape/architecture lens at f/4 to f/8, it works just fine. The astrophotography crowd might not exactly feel true love for this lens, but they probably won't dismiss it, either. 

At the price, it's easy to recommend. 

Recommended (2021 to present)

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