Sony 20-70mm f/4 G Review: A Mostly Excellent Zoom Lens

As the mirrorless camera market hits its stride and companies have caught up on their typical prime and zoom lens offerings, we see new offerings in non-traditional focal lengths. I can’t remember writing the words “all-in-one” in my decades in the tech press world as I have in the last year.

Author’s note: In addition to this review you can find more images and additional thoughts about this lens in my YouTube video review below. 

It feels like every time I look in my email box there’s a press release about a new “all-in-one” lens with some hitherto unseen combination of focal lengths. In the last few months, I’ve reviewed the Tamron 50-400mm f/4.5-6.3 Di III VC VXD lens, the Tamron 20-40mm f/2.8 Di II VXD and the Sigma 60-600mm f/4.5-6.3 DG OS HSM Sport lens, to name a few.

Maybe by comparison, the Sony 20-70mm f/4 G doesn’t seem like that much of a specialty lens; after all, it’s only four millimeters wider than the Sony 24-70 f/2.8 GM II lens, and it has an f/4 aperture, which is a stop slower than the G Master lens as well. But the Sony 20-40 F4 G has hit a sweet spot in lens design, and it comes in at the $1,000 price sweet spot, which is the upper limit for many entry-level photographers shopping for their primary lens.

The lens is small and lightweight, but instead of giving up image quality, resolution, and speed for the compact size and weight (as do many manufacturers), Sony has decided to make the maximum aperture f/4 instead of f/2.8.

I have to admit that I’m not a fan of most f/4 counterpart lenses where a successful f/2.8 lens already exists. I understand the need for different prices in optics, but I’m generally not impressed with the f/4 iteration of an f/2.8 lens, and I also expected that to be the case with this lens.

I was wrong. I’m pretty smitten with this lens. It’s not perfect, but for every place, it falls short, there are several other places where it does well.

A Story of Degrees

The full specs for the Sony 20-70mm f/4 G lens are in our launch coverage, but I’ll touch on the ones that relate to or impact the performance of this lens.

The starting place with the 20-70mm f/4 G lens is naturally that odd focal length choice. It doesn’t seem like there would be a lot of difference between the 24mm and 20mm widest focal lengths. After all, that’s only a 4mm difference.

The truth is that focal length doesn’t matter so much as the field of view, the amount of a scene that can be captured by a lens measured in degrees. A fisheye lens sees about 180 degrees horizontally. Even though including peripheral vision, human eyesight is about 130 degrees (combined eyes), our main field of view is 40 to 60 degrees.

The difference between a 20mm and 24mm lens is 10 degrees. The difference between 28mm (as on the Tamron 28-75) is 18 degrees. This is a much more significant difference than the field of view change from 70 to 75mm, which is only 1.8 degrees.

Put another way, the four-millimeter difference between 20mm and 24mm is five times greater than the difference from 70mm to 75mm.

From a field-of-view standpoint, the 20mm focal length is a big deal. It’s enough for many people to skip purchasing a 16-35mm lens, making the 20-70mm lens a substitute for two separate lenses.

The lens is just around four inches tall and weighs 17.2 ounces, which is perfect for a travel and all-around lens. There are some lenses I can’t stand to bring around due to their weight, but the Sony 20-70mm isn’t one of those lenses.

Sony put a lot of emphasis on the video capabilities of this lens, as it has on all its recent lenses. The company has seen the shift to video content creation and has rolled out linear motors in nearly all recent offerings. Inside the lens are dual XD linear motors, giving this lens fast-focusing capabilities and utterly silent operation in video shooting.

Sony says these tiny motors are primarily responsible for the size savings, but that hasn’t kept Sony from putting high-end optics in this lens. The 20-70mm f/4 G features two AA (Advanced Aspherical) elements, three ED (Extra-low Dispersion) elements, and one ED aspherical lens. These specialized optical elements reduce chromatic and aspherical aberrations and suppress flaring, which they do for the most part.

There was a noticeable flare when shooting wide-open directly into the sunlight, though flare is to be expected when shooting directly into the sun. The Sony 24-70mm f/2.8 GM II also exhibited flare in the same scene, with much more significant suppression of the flare and better handling of exposure across the frame.

Lens Controls and Use

Sony started putting manual aperture control rings on its GM lenses and has since included the same aperture control on many G lenses. I love having aperture controls on the lens, because it makes the shooting experience more flexible and precise.

While I can change the aperture with the rear thumb dial without an on-lens-ring, there’s no way to select Auto aperture with this setup. Having on-lens aperture controls also allows me to put the camera in manual mode and use the Auto setting on the aperture ring to essentially make the camera shutter-priority, then return to complete manual control when sliding the aperture out of the Auto setting.

The lens is water and dust resistant (including gaskets on the lens mount) and includes a switch to toggle between click and de-clicked aperture, two programmable focus, and hold buttons. There is also a switch to toggle between manual and autofocus modes.

The lens is very comfortable to hold and use, although the small size makes things more cramped when wearing gloves. The focus ring and zoom ring are large and easy to grab, even gloved, and when it’s cold, I use the rear dial to control the aperture.

In Use and Image Quality

As a reminder, I’ve never been a fan of f/4 lenses, but I’m willing to change with the times. Lens design has improved markedly over the last few years, and this lens is a perfect example of how sound engineering can overcome bad reputations.

The Sony 20-70mm has quickly become my favorite travel lens. Thanks to quite a bit of travel over the month, which is coincidentally the amount of time I’ve had this lens in order to review it, I’ve gotten to use it on everything from portraits to landscapes and street photography to photojournalism.

I’ve also brought the Sony 24-70mm f/2.8 GM II for all of these trips, though it ended up staying in my hotel room or my bag most of the time. I brought the 24-70mm out on a few of my shoots in Las Vegas so I could compare the two lenses directly, but otherwise, I went for the 20-70mm each time I picked up my camera.

Images from the GM are sharper and have better contrast when pixel peeping, but these are hard to spot at a typical on-screen viewing resolution. tt f/4 and at a 24mm focal length, these lenses are hard to tell apart.

Even the f/2.8 aperture is hard to spot as a difference when shooting landscapes or other scenes with a distant subject, although side-by-side with an f/4 image for portraits or other near-subject scenes versus the f/2.8 of the GM II, it’s easy to pick out the f/4.

The images from the 24-70mm GM II have less distortion at 24mm than those from the 20-70mm, but that is not hard to accomplish. In many images, the 20-70mm F4 G has typical distortion caused by the broad field of view, though some images exhibit much more distortion than others. In my rough field tests, this is aggravated by setting the focus point off the horizontal center.

In this 20mm image below, the tower outside the Venetian hotel appears to bow in the middle and then curve inwards, and I recollect that the focus point was on the top of the tower since this started as a test of flare sun stars.

On more typical wide-angle shots, distortion is nearly non-existent in the center of the frame and the detail in these areas is spectacular. This forty-second exposure has a remarkable amount of detail thanks to the a7R V’s 61-megapixel sensor.

On one of my days in Las Vegas, I emerged from the CES trade show to discover an unexpected demonstration. Organized by families of those that died when Flight PS752 was shot down, the peaceful protests are staged regularly around the country and are trying to bring attention to the political situation in Iran. I photographed for more than a half-an-hour, talking to the attendees and promising to send them images.

In addition to being very moving, this demonstration is an excellent eye-AF testing area and a good place to test lens resolution. The various signs and posters had a detail that held up to pixel peeping, and the sun positioned directly behind the protest allowed me to test flaring.

When shooting directly into the sun, there is a considerable amount of flaring, with some of the image overexposed by about a stop, but the flaring disappears when stopped down. I took the opportunity to switch to the 24-70mm GM here and found it would also flare under the same conditions, though much less and with less overexposure in the affected areas.

I also found having the 20mm lens to photograph protesters was handier than the f/2.8 aperture, so I returned to using the 20-70mm f/4 G.

There are few image quality issues aside from the flaring. I tried very hard to spot errant chromatic aberration but couldn’t find anything that isn’t easily corrected in the software. In short, image quality is excellent and is one of the things that draws me to this lens.

Video Use

Video operation is smooth and silent with the 20-70mm f/4 G, as has been the case with Sony’s recent lenses.

There is one odd video-related issue I’m still trying to diagnose. Sony told us that the lens was designed for “handheld” vlogging use, and it is… mostly.

The minimum focal distance on the 20-70mm is around ten inches, close enough that I could be able to get my face in focus while hand-holding with no issues, yet about thirty percent of the time, the 20-70mm F4 G and my Sony Alpha 1 wouldn’t focus on my eyes or would focus on my eyes, and then jump off my eyes and lose focus for the rest of the clip.

These eye-AF issues happened mainly in Las Vegas (but not only there) since I was shooting vlog tests and in several instances, the focus locked on a background object and stayed there. I’d chalk this up to autofocus in the camera, but I’ve never seen the Alpha 1 miss eye-detect autofocus, and I even have a clip from my shoot where I read my settings out to the camera as I verified I was in the eye-detect AF.

Once when it happened in Vegas, I could switch to the G Master, which did not have the issue, and then switch back to the 20-70mm G, but it didn’t crop back up.

I’ve done tests in my office, and it seems I can focus closer than ten inches away from my eye. This was likely a camera issue, but since it happened multiple times with this lens and has never happened with another lens, I feel I should mention it.

I had no other issues with the lens for video use, and the 20mm focal length is excellent for the crop inherent with active stabilization. A 20mm lens at a 1.2x crop of image stabilization is 24mm, which gives an excellent field of view equivalence to a 24mm still image.

Excellent Despite Some Flaws

The Sony 20-70mm f/4 G is genuinely excellent glass and has entered the increasingly crowded list of “lenses I would buy for myself.”

It is small and lightweight and has image quality performance that is typically only found way above its asking price. It’s also a smart secondary lens for a photographer with a 24-70mm f/2.8 and a 16-36mm that wants to be able to back those up with a single lens or who wants the versatility of those focal lengths without having to bring the whole camera bag.

There are exchanges made for the small size and the (relatively) low price, but they are all equal to the lens’s versatility. The increased field of view makes up for some of these shortcomings by opening up new photographic possibilities. I started as a skeptic but ended up a fan.

Are There Alternatives?

Though there are many alternatives at this odd focal length, they are only somewhat comparable. As I’ve mentioned, I love the Tamron 20-40mm f/2.8 Di III VXD, though you lose 30mm on the long side to get the 20mm focal length.

The Tamron 28-75mm Di III VXD G2 is also a solid performer at $700. I found 28mm too long to rely on as my only travel lens. Sigma doesn’t have a non-traditional focal length, but it does offer the 24-70mm ART lens, which does not focus nearly as well as the Sony 20-70mm f/4 G.

Should You Buy It?

Yes, especially if you are looking for a travel or everyday lens and your priority is size and price over (one stop of) bokeh, this one is for you.