Tamron 20mm f/2.8 Di III OSD M1:2 Lens Review

The Tamron 20mm f/2.8 Di III OSD M1:2 Lens is the last of three similar simultaneously announced close-focusing compact wide-angle prime lenses to reach our hands. As I said in the 35mm f/2.8 Di III OSD Lens review, Tamron has been turning heads with their recently-introduced Di III mirrorless camera lenses, introducing one attractively-priced, impressive-performing lens after another. This lens meets the expectations set by its predecessors, providing great image quality from a compact, lightweight package at a low price.

Can you tell the three referenced lenses apart? Without being able to see the focal length number printed on the side, I cannot.

Focal Length

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The focal length should always be a primary consideration for a lens purchase or selection for use. Focal length matters greatly because it drives subject distance choices with perspective determined by those distances.

Landscape photography is a perfect use for a 20mm lens. This focal length is wide and can allow an entire scene to remain in focus. While perhaps slightly more challenging to compose landscapes with than the ultra-popular 24mm angle of view, the somewhat-less-popular 20mm focal length has its advantages including a better emphasis on foreground subjects. It is unusual that I do not have a lens covering 20mm when I am photographing landscapes.

Architectural photography, large product photography, interior photography, birthday parties ... are just a few uses for 20mm. This is a great focal length to leave mounted for documenting life in general.

Wedding and event photography often utilize a wide-angle lens for capturing the large scene, for environmental-type portraits, and for group portraits including in tight spaces. Even groups of your largest subjects will likly fit in the frame with this focal length.

Photojournalist's needs are often similar to those of a wedding photographer and can also make use of 20mm. Videographers can find the 20mm focal length to be just right for some needs.

While telephoto lenses are more frequently used for sports, a 20mm angle of view allows a different perspective on these events. This focal length can be used to capture the big picture of the venue, overhead shots of the athletes and their coaches being interviewed after the game, and, when access permits, full-body environmental action sports photos showing lots of venue in the background. Note that when used for action sports with a rapidly approaching subject, a 20mm angle of view makes the capture of the perfect pose at the perfect framing distance challenging due to the subject changing size in the frame rapidly at short distances.

Following are examples of what this focal length looks like on a full-frame camera along with a few other common wide-angle focal lengths:

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When used on an ASP-C/1.5x FOVCF sensor format camera, this lens's angle of view is similar to that of a 30mm lens on a full-frame camera, similar to the hugely-popular 35mm angle of view. While many of the uses for this AOV remain the same as for 20mm, the narrower angle of view obviously requires more distance for the same subject framing and the longer distance changes the perspective modestly. The full-frame 30mm angle of view is typically favored over 20mm for portrait photography.

Max Aperture

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All three of the simultaneously-announced Tamron Di III primes feature an f/2.8 aperture. An f/2.8 max aperture is relatively wide and few zoom lenses covering this focal length range have wider apertures with kit lenses typically having considerably narrower 20mm apertures. While some of the other 20mm prime lenses have an f/2.8 max aperture, I can think of none with a narrower max aperture. So, this lens opens wide relative to zoom lenses and not wide relative to prime lenses, a result of the ultra-light weight, tiny size, and low-price formula. Smaller lens elements usually have a cost-reduction value as well.

Use a wider aperture to stop action in less light and enable handholding in similarly-lower light levels. In addition to allowing more light to reach the sensor, permitting faster shutter speeds and/or lower ISO settings, increasing the aperture opening permits a stronger, better subject-isolating background blur at this focal length.

The following aperture comparison example takes a closer look at the background blur aspect.

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When viewed at full size, the differences appear stronger. Compare the widest 20mm aperture currently available in your kit with f/2.8.

Wide-angle lenses cannot blur the background like telephoto lenses and with 20mm options having an up-to-2-stop-wider aperture available, this lens cannot blur the background as well as some alternatives. With an extremely short minimum focusing distance assisting, this lens can produce a strong blur relative to its available max aperture.

The above image shows the maximum background blur this lens can produce.

Image Stabilization

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This lens is not optically stabilized, but with current Sony E-mount full-frame cameras, Sony generally takes care of that omission with Steady Shot or IBIS (In-Body Image Stabilization). On a traditional DSLR with an optical viewfinder, IBIS results in an unstabilized view, meaning that stabilization was not helpful for composition or for providing a still subject to the camera's AF system. With EVFs being prevalent in Sony's lineup, the viewfinder image is being read from the imaging sensor and that is stabilized. Therefore, the viewfinder image is nicely stabilized and sensor-based AF takes advantage of the stabilized view for improved accuracy.

Image Quality

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This lens does not have the widest aperture available in a 20mm model and it is generally expected that lenses are not as sharp at their wide-open apertures as they are when stopped down one or two stops. A moderately wide max aperture lens that needs to be stopped down for adequate sharpness negates a strong reason for using a prime lens in the first place. Fortunately, like its two siblings, this lens is sharp wide-open.

In the center of the frame, this lens is sharp at f/2.8 and with some contrast and resolution increase at f/4, it becomes razor sharp. The only reason to stop down to f/5.6 is for increased depth of field.

In general, lenses are not as sharp in the periphery where light rays must be bent more strongly than they are in the center. In this regard, this lens is an above-average performer with corners having good sharpness at f/2.8 and steadily improving in this regard until good at f/5.6.

Below you will find sets of 100% resolution center of the frame crops captured in uncompressed RAW format using a Sony a7R III. The images were processed in Capture One using the Natural Clarity method with the sharpening amount set to only "30" on a 0-1000 scale (Note that images from most cameras require some level of sharpening but too-high sharpness settings are destructive to image details and hide the deficiencies of a lens).

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Be sure to find details in the plane of sharp focus to base your opinions on. The f/2.8 examples are quite impressive until the f/4 samples are viewed.

Focus shift, the plane of sharp focus moving forward or backward as the aperture is narrowed (residual spherical aberration or RSA), is not an issue with this lens (many modern lenses automatically adjust to correct for this).

Next, we'll look at a comparison showing 100% extreme-top-left-corner crops captured and processed identically to the above center-of-the-frame images. These images were manually focused in the corner of the frame.

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The results improve as the aperture is narrowed and most are going to be happy with their results from this lens.

Corner sharpness does not always matter but it does matter for many disciplines including landscape photography. When I'm photographing landscapes with corner sharpness being desired, I'm probably using f/8 or f/11 to obtain enough depth of field for in-focus corner details and this lens works beautifully for this purpose at these apertures. When shooting at wide apertures, the corners are most often out of focus and not supposed to be sharp. Videos captured at normal wide-aspect ratios also avoid use of the corners.

Some peripheral shading shows in the wide-aperture corners. This is normal and expected. There are about 3.5 stops of vignetting in the corners at f/2.8. Stop down one stop and about 1 stop of shading clears. By f/8, about 2 stops of shading, a noticeable amount, remains present in the corners and the further reduction realized through the balance of the aperture range is minor.

APS-C format cameras using lenses projecting a full-frame-sized image circle avoid most vignetting problems. In this case, the about-1.5-stops of shading showing at f/2.8 might be visible in images with a solid color (such as a blue sky) showing in the corners.

One stop of shading is the amount often used as the visibility number, though subject details provide a widely-varying amount of vignetting discernibility. Vignetting can be corrected during post-processing with increased noise in the brightened areas being the penalty or it can be embraced, using the effect to draw the viewer's eye to the center of the frame.

The effect of different colors of the spectrum being magnified differently is referred to as lateral (or transverse) CA (Chromatic Aberration). Lateral CA shows as color fringing along lines of strong contrast running tangential (meridional, right angles to radii) with the mid and especially the periphery of the image circle showing the greatest amount as this is where the greatest difference in the magnification of wavelengths typically exists.

With the right lens profile and software, lateral CA is often easily correctable (often in the camera) by radially shifting the colors to coincide though it is always better to not have the problem in the first place. Any color misalignment present can easily be seen in the site's image quality tool, but let's also look at a worst-case example, a 100% crop from the extreme top left corner of an ultra-high resolution a7R III frame showing diagonal black and white lines.

There should be only black and white colors in these images and the additional colors are showing the presence of lateral CA. That is a moderate amount of color separation, especially for a prime lens.

A relatively common lens aberration is axial (longitudinal, bokeh) CA, which causes non-coinciding focal planes of the various wavelengths of light, or more simply, different colors of light are focused to different depths. Spherical aberration along with spherochromatism, or a change in the amount of spherical aberration with respect to color (looks quite similar to axial chromatic aberration but is hazier) are other common lens aberrations to look for. Axial CA remains at least somewhat persistent when stopping down with the color misalignment effect increasing with defocusing while the spherical aberration color halo shows little size change as the lens is defocused and stopping down one to two stops generally removes this aberration.

In the real world, lens defects do not exist in isolation with spherical aberration and spherochromatism generally found, at least to some degree, along with axial CA. These combine to create a less sharp, hazy-appearing image quality at the widest apertures.

In the examples below, look at the fringing colors in the out of focus specular highlights created by the neutrally-colored subjects. Any color difference is being introduced by the lens.

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A moderate but not unusual amount of color separation is showing in these examples.

Flare and ghosting are caused by bright light reflecting off of the surfaces of lens elements, resulting in reduced contrast and sometimes-interesting artifacts. Tamron uses BBAR (Broad-Band Anti-Reflection) Coating to minimize these effects and the low 10/9 elements/groups count is especially helpful for this lens. Even with the sun in the corner of the frame and the aperture stopped down to f/16, this lens creates only minor flare effects.

Flare effects can be embraced, avoided, or removal can be attempted. Removal is sometimes challenging.

Two lens aberrations are particularly evident when shooting images of stars, mainly because bright points of light against a dark background make them easier to see. Coma occurs when light rays from a point of light spread out from that point, instead of being refocused as a point on the sensor. Coma is absent in the center of the frame, gets worse toward the edges/corners, and generally appears as a comet-like or triangular tail of light which can be oriented either away from the center of the frame (external coma), or toward the center of the frame (internal coma). Coma clears as the aperture is narrowed. Astigmatism is seen as points of light spreading into a line, either sagittal (radiating from the center of the image) or meridional (tangential, perpendicular to sagittal). Remember that lateral CA is another aberration apparent in the corners.

The image below is a 100% crop taken from the top-left corner of a Sony a7R III frame.

While these stars are not perfectly round, they are round in comparison to those created by many alternative lenses.

Like this lens's 24mm sibling, our distortion test result screams "Correction required!" The amount of barrel distortion this lens shows is extreme, approaching fisheye lens proportions and, uncorrected, the geometric distortion is going to be obvious when straight lines are placed in the periphery of the frame. Most modern lenses have lens correction profiles available for the popular image processing software (or in-camera) and distortion can be easily removed using these, but geometric distortion correction requires stretching which is detrimental to image quality. Some portion of the image must be stretched or the overall dimensions must be reduced. It appears that Tamron is expecting the correction option to be taken for this lens.

The amount of blur a lens can produce is easy to show (and was shown earlier in the review). Assessing the quality is more challenging in part because of the infinite number of variables available. I'll first share a pair of 100% crop f/11 (for aperture blade interaction) examples.

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The first example shows that an unusual bright blob is present in the defocused highlights. The second example shows a strongly blurred outdoor scene that appears nicely rendered. The last example is a full image reduced in size and also looks nice.

Except for a small number of specialty lenses, the wide aperture bokeh in the corner of the frame does not produce round defocused highlights with these effects taking on a cat's eye shape due to a form of mechanical vignetting. If you look through a tube at an angle, similar to the light reaching the corner of the frame, the shape is not round and that is the shape seen in the corners. The example below shows the top-left quarter of the frame.

With close inspection of this sample, the referenced bright blob showing in defocused hightlights can be seen extending into the corner at f/2.8. As the aperture narrows, the entrance pupil size is reduced and the mechanical vignetting absolves with the shapes becoming round.

With a 7-blade count aperture, point light sources captured with a narrow aperture setting and showing a sunstar effect will have 14 points, as illustrated in the f/16 example below.

My preference is for single-flaring points, but this result is still looking good.

In summary and just like the 24mm sibling: this lens's most prominent image quality shortcoming is the strong barrel distortion, it shows a moderate amount of color separation, and it has vignetting that does not resolve without correction. It is the Tamron 20mm f/2.8 Di III OSD M1:2 Lens's excellent sharpness that will have photographers overlooking those other aspects.

Focusing

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Like its same-time-introduced siblings, this lens's AF system is powered by Tamron's "OSD" "Optimized Silent Drive" stepping motor. As discovered with the 24mm and 35mm lenses, this is not my favorite AF system.

Testing on the Sony a7R IV, this lens focuses relatively quickly and relatively quietly (light clicks and the motor are heard) in AF-C continuous focus mode. In AF-S single shot focus mode, focusing becomes slow with hunting being the norm before the camera locks focus and an audible click can be heard with each direction change. As with its 24mm and 35mm siblings, the focus speed is adequate for most logical uses for this lens and short focus distance changes happen faster than long ones.

Low-light-autofocus performance is just OK (slow).

While this lens does not change overall size during focusing, it is a front-focusing model and the front element extends a significant amount inside the lens barrel as illustrated above. The lens is parked to the retracted state when the camera powers off. Note that the lens does not precisely return to the minimum focus distance upon powering back on - refocusing will be required in that situation.

AF accuracy is always paramount and this lens performs well in this regard.

Normal is for the scene to change size in the frame (sometimes significantly) as focus is pulled from one extent to the other, referred to as focus breathing, a change in focal length resulting from a change in focus distance. Focus breathing negatively impacts photographers intending to use focus stacking techniques, videographers pulling focus, and anyone critically framing while adjusting focus. While this lens shows a significant amount of focus breathing, keep in mind that it also focuses closely, providing a high maximum magnification.

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FTM (Full Time Manual) focusing is supported via Sony's DMF (Direct Manual Focus) AF mode. This lens does not have an AF/MF switch, meaning that a camera setting change is required to switch modes. As I've said many times before, I miss the switch.

The plastic-ribbed focus ring is reasonably large and easily tactilely distinguishable from the balance of the lens barrel. This ring is smooth and has a nice amount of resistance. This is a variable response MF ring. Turn it quickly and about 360° (long for the fast speed) of rotation will complete the full extent focus adjustment. When turned slowly, about 4.5 full rotations (a crazy 1620 °) are required to make a full range focus distance adjustment, allowing precise manual focusing even at close distances. Annoying is the lag and distance adjustment jump encountered when changing ring directions, making manual focusing more challenging than it should be. The scene moving around slightly during focusing is similarly annoying (if watching closely).

Tamron does not provide focus distance information on the lens, such as in a window, but this information is available in the Sony viewfinder and rear LCD.

With a 4.3" (109mm) minimum focus distance, this lens has an impressive best-in-class 0.50x maximum magnification spec.

There are few identically-specced lenses, so I'll expand the criteria used for this selection, staying within the full-frame boundary:

Model	Min Focus Distance "(mm)		Max Magnification
Canon EF 20mm f/2.8 USM Lens	9.8	(250)	0.14x
Nikon 20mm f/1.8G AF-S Lens	7.9	(201)	0.23x
Nikon 20mm f/2.8D AF Lens	10.2	(259)	0.12x
Rokinon (Samyang) 20mm f/1.8 ED AS UMC Lens	7.9	(200)	x
Sigma 20mm f/1.4 DG HSM Art Lens	10.9	(277)	0.14x
Sigma 20mm f/1.8 EX DG Lens	7.9	(201)	0.25x
Sony FE 20mm f/1.8 G Lens	7.1	(180)	0.22x
Tamron 20mm f/2.8 Di III OSD Lens	4.3	(109)	0.50x
Tamron 24mm f/2.8 Di III OSD Lens	4.7	(119)	0.50x
Tamron 35mm f/2.8 Di III OSD Lens	5.9	(149)	0.50x
Tamron 17-28mm f/2.8 Di III RXD Lens	7.5	(190)	0.19x
Tamron 28-75mm f/2.8 Di III RXD Lens	7.5	(190)	0.34x
Zeiss 21mm f/2.8 Milvus Lens	8.7	(220)	0.20x
Zeiss 21mm f/2.8 Classic Lens	8.7	(220)	0.20x

A subject measuring approximately 2.7 x 1.8" (69 x 46mm) will fill the frame at the minimum focus distance. Each nut in the minimum-focus-distance-captured image below measures 0.74" (18.7mm) in diameter.

Center of the frame image quality is good at minimum focus distance but the periphery remains soft even at narrow apertures with strong lateral CA having influence.

Need a shorter minimum focus distance and greater magnification? An extension tube mounted behind this lens should provide a significant decrease and increase respectively. Extension tubes are hollow lens barrels that shift a lens farther from the camera, which permits shorter focusing distances at the expense of long-distance focusing. Sony and Tamron do not publish extension tube specs nor do they manufacture these items, but third-party Sony-mount extension tubes are available. Note that at minimum focus distance, there is only about 1.2" (30mm) of working space in front of the sans-hood lens and likely only short extension tubes would be usable with subject lighting becoming challenging. The shadowing caused by the end of the lens can be seen in the previous example.

This lens is not compatible with Tamron or Sony teleconverters.

Build Quality & Features

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Tamron's current lens designs, featuring a matte black finish and white printing in a modern font, are visually attractive. Their lenses are also physically comfortable to use and have a nice quality feel.

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The exterior lens barrel features quality plastic construction.

This lens has moisture resistance incorporated into its design, including a mount gasket seal.

"The front surface of the lens element is coated with a protective fluorine compound that is water- and oil-repellant. The lens surface is easier to wipe clean and is less vulnerable to the damaging effects of dirt, dust, moisture and fingerprints." [Tamron]

Tamron indicates that this lens "... is compatible with many of the advanced features that are specific to mirrorless cameras." These features include hybrid AF, Eye AF, Direct Manual Focus (DMF), in-camera lens correction (shading, chromatic aberration, distortion), and camera-initiated lens firmware updates.

This is a small, extremely light lens. It is pleasant to carry for even long periods.

Model	Weight oz(g)		Dimensions w/o Hood "(mm)		Filter	Year
Canon EF 20mm f/2.8 USM Lens	14.3	(405)	3.1 x 2.8	(78.0 x 71.0)	72	1992
Nikon 20mm f/1.8G AF-S Lens	12.6	(357)	3.2 x 3.1	(81.3 x 78.7)	77	2014
Nikon 20mm f/2.8D AF Lens	9.5	(270)	2.7 x 1.7	(69.0 x 42.5)	62	1994
Rokinon (Samyang) 20mm f/1.8 ED AS UMC Lens	17.5	(497)	3.3 x 3.5	(83.0 x 88.4)	77	2016
Sigma 20mm f/1.4 DG HSM Art Lens	33.5	(950)	3.6 x 5.1	(90.7 x 129.8)		2015
Sigma 20mm f/1.8 EX DG Lens	18.4	(520)	3.5 x 3.4	(89.0 x 87.0)	82
Sony FE 20mm f/1.8 G Lens	13.2	(373)	2.9 x 3.3	(73.5 x 84.7)	67	2020
Tamron 20mm f/2.8 Di III OSD Lens	7.8	(221)	2.9 x 2.5	(73.0 x 63.5)	67	2019
Tamron 24mm f/2.8 Di III OSD Lens	7.6	(215)	2.9 x 2.5	(73.0 x 63.5)	67	2019
Tamron 35mm f/2.8 Di III OSD Lens	7.4	(210)	2.9 x 2.5	(73.0 x 63.5)	67	2019
Tamron 17-28mm f/2.8 Di III RXD Lens	14.8	(420)	2.9 x 3.9	(73.0 x 99.0)	67	2019
Tamron 28-75mm f/2.8 Di III RXD Lens	19.4	(550)	2.9 x 4.6	(73.0 x 117.8)	67	2018
Zeiss 21mm f/2.8 Milvus Lens	30	(851)	3.8 x 3.7	(95.5 x 95.0)	82	2015
Zeiss 21mm f/2.8 Classic Lens	21.2	(600)	3.4 x 4.3	(87.0 x 109.0)	82	2010

For many more comparisons, review the complete Tamron 20mm f/2.8 Di III OSD M1:2 Lens Specifications using the site's lens specifications tool.

Visual size comparisons are always useful. I'll surround the three Tamron prime siblings with a pair of Tamron zooms.

Positioned above from left to right are the following lenses:

Tamron 17-28mm f/2.8 Di III RXD Lens
Tamron 20mm f/2.8 Di III OSD Lens
Tamron 24mm f/2.8 Di III OSD Lens
Tamron 35mm f/2.8 Di III OSD Lens
Tamron 28-75mm f/2.8 Di III RXD Lens

The same lenses are shown below with their hoods in place.

Use the site's product image comparison tool to visually compare the Tamron 20mm f/2.8 Di III OSD M1:2 Lens to other lenses.

This lens has 67mm filter threads. 67mm filters are medium in size, modest in cost, and common in popularity. Extremely convenient is that many of Tamron's recently introduced Di III lenses use the 67mm filter size, permitting one set of effects filters to be shared by all lenses in a Di III kit without the need for step-up filter adapter rings.

We are seeing a strong increase in peripheral shading when using a standard thickness circular polarizer filter and even standard thickness protection filters produce significant mechanical vignetting. Slim models such as the Breakthrough Photography X4 circular polarizer filter help significantly but this specific filter still shows hard vignetting at f/2.8. Only a small amount of this hard vignetting remains at f/11.

Tamron always includes the hood. The bayonet-mount rigid molded plastic petal-shaped Tamron HF050 hood (same as the 24mm Di III) is rather small. The protection it offers from bright light and impact is not huge but it is still worth using this hood. Its compactness is nice.

Tamron does not include a case with this lens. Consider a small Lowepro Lens Case or Think Tank Photo Lens Case Duo for a quality, affordable single-lens storage, transport, and carry solution.

Lens caps are a very-frequently-used accessory and Tamron's have long been great.

Tamron emphasizes that this lens was "Designed in Japan" but in fine print admits that it was "Made in Vietnam" with the lens hood "Made in Philippines".

Price, Value, Compatibility

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Tamron's name has been synonymous with good value and this lens is that. Just like its 35mm sibling, the nicely-designed Tamron 24mm f/2.8 Di III OSD Lens provides great image quality for a bargain-grade price.

Tamron's Di III lenses are designed for use on mirrorless interchangeable lens cameras. At review time, the Tamron 20mm f/2.8 Di III OSD Lens specifically is compatible with all Sony E-mount cameras, including both full-frame and APS-C sensor format models.

"This product is developed, manufactured and sold based on the specifications of E-mount which was disclosed by Sony Corporation under the license agreement with Sony Corporation." [Tamron] Tamron provides a 6-year limited warranty.

The reviewed Tamron 20mm f/2.8 Di III OSD Lens was online-retail sourced.

Summary

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Again, as with its siblings, a lot of photographers are going to purchase the Tamron 20mm f/2.8 Di III OSD Lens for its value proposition. This little ultra-light lens delivers excellent image sharpness, especially for the price.

What are this lens's shortcomings? Very strong barrel distortion is at the top of my list. Some color separation and vignetting that does not completely resolve even at the narrowest apertures are additional image quality limitations.

The autofocus system is this lens's biggest physical weakness. Related is that the manual focus distance adjustment jumps when changing focus ring direction, making manual focusing more challenging than it should be.

The f/2.8 aperture isn't so wide for a 20mm prime lens, but that max aperture opening is part of the small, light, and inexpensive formula. Like the rest of the Tamron Di III lenses I've reviewed, this one's light weight does not exude rugged build quality confidence, but this lens seems nicely built with tight tolerances and it looks great. A long warranty indicates that Tamron expects the lens to hold up for a long time.

The 20mm f/2.8 Di III OSD Lens is yet another great Tamron deal.