Sigma 20mm F1.4 DG DN Art Lens Review

The Sigma 20mm F1.4 DG DN Art Lens is "The world's first 20mm F1.4 full-frame mirrorless lens." [Sigma] "It is the first and only lens of this specification, joining its predecessor – the 20mm F1.4 DG HSM | Art – as the only 20mm F1.4 lenses available for full-frame platforms." [Sigma]

World records are especially fun when they serve an important photography need. In this case, astrophotography is one of the foremost needs aided by this lens's defining specifications. This demanding pursuit requires the ultimate performance from an extremely wide aperture to render stars as tack-sharp tiny dots across the entire frame. Most lenses fall short of this requirement, especially showing stretched stars in the frame corners. Not this one — it performs at the top of its class.

I regard the Sigma 20mm F1.4 DG DN Art Lens as the ultimate astrophotography lens — essentially a match for the slightly longer Sony FE 24mm F1.4 GM Lens.

The Sigma 20mm F1.4 DG DN lens delivers outstanding f/1.4 sharpness at infinity and excellent image quality overall. Like the rest of the Sigma Art lenses, this one features great build quality, excellent physical performance, and pleasing aesthetics for a reasonable price.

As this lens and the Sigma 24mm F1.4 DG DN Art Lens were announced and delivered simultaneously, the two reviews were also created at the same time. With the lenses sharing many similarities, the reviews will also.

Focal Length

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The focal length (or the focal length range for a zoom lens) is the first attribute to consider for lens selection. Focal length drives subject distance choices, which determine perspective.

Ultra-wide-angle focal lengths are a lot about making foreground subjects large in relation to the background subjects and about including a lot of background in the frame. The 20mm angle of view allows a lot of subject in the frame despite a short working distance and is notably able to give the viewer a sense of the presence in the images captured by it.

I consider the 20mm angle of view ideal for "scapes". This lens is useful for photographing most scenes that "scapes" can be naturally appended to, including landscapes, nightscapes, cityscapes, buildingscapes, roomscapes, etc.

When two wide-angle f/1.4 lenses promoted as ideal for photographing the Milky Way (an addicting pursuit) show up in the same box with a dark, cloudless sky predicted for the next evening, you drop everything and drive hours to the darkest sky location in the region. In this case, that location was Cherry Springs State Park, an International Dark Sky Park near Coudersport, Pennsylvania.

After a few hours of sleep and especially after loading the photos from the memory cards, you forget about arriving home at 2:30 AM.

Include peoplescapes in the scapes list, with environmental photos of individuals and groups captured at a wide range of locations from scenic landscapes to birthday parties in small rooms being a 20mm capability. Note that if multiple people are in the 20mm frame, their distance from the camera should not vary by a significant amount. Otherwise, the people in front will appear larger than those in the back. Also, avoid getting too close to people to avoid perspective issues.

This is a great wedding lens.

Photographing architecture? 20mm is a great focal length choice for that pursuit.

While the 20mm angle of view is rather wide for use as a general-purpose lens without at least one additional focal length available, there are general-purpose uses for 20mm. I've used 20mm to capture an entire day of family holiday festivities. This is a fun lens to carry around with a creative purpose.

Videographers will find a host of uses for 20mm.

I like to look at focal lengths in comparison format and since this lens has only one focal length, I'll borrow a comparison from the Canon EF 16-35mm f/4L IS USM Lens review.

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On an ASP-C/1.5x sensor format body, the 20mm focal length provides an angle of view similar to a 30mm lens on a full-frame sensor format body with an angle of view just slightly narrower than the 28mm example shared above. The 30mm angle of view is only moderately wide and just wider than the ultra-popular and useful 35mm focal length. While there is some overlap in usage between the 20mm and 30mm focal lengths, they are rather different, with 30mm having more general-purpose appeal and uses that more closely align with the 35mm focal length.

The 20mm APS-C angle of view is a great choice for capturing a natural perspective. It is wide enough to capture the big scene but not so wide that people and other subjects are readily distorted by the close perspective invited by ultra-wide angles.

The 30mm full-frame-equivalent angle of view is a great choice for photojournalistic uses. Wedding and portrait photographers like 30mm, especially for full to mid-body portraits and for group portraits.

Landscape photographers have plenty of use for the 30mm angle of view. 30mm is also popular with videographers, especially for creating documentaries.

Many medium and large products can be captured at the 30mm angle of view, and I'm always happy when a lens with the same or similar angle of view (or a zoom covering this angle of view) comes across my desk because I know that I can assign it around-the-house use.

The entire list of 20mm full-frame and APS-C angle of view uses is long, and I've only scratched the surface here.

Max Aperture

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It doesn't get wider than this at 20mm (and most other focal lengths). 20mm is also the widest AF full-frame focal length to open to f/1.4 — no wider-angle lenses have an f/1.4 aperture.

The f/1.4 refers to the maximum aperture, the ratio of the focal length to the entrance pupil diameter, available in this lens. The lower the aperture number, the wider the opening, and the more light the lens can deliver to the imaging sensor. Each "stop" in aperture change (full stop examples: f/1.4, f/2.0, f/2.8, f/4.0) increases or decreases the amount of light by a factor of 2x (a substantial amount).

The additional light provided by wider aperture lenses permits sharp images of subjects in motion and with the camera handheld in lower light levels and with lower (less noisy) ISO settings. In addition, increasing the aperture opening provides a shallower DOF (Depth of Field) that creates a stronger, better subject-isolating background blur (at equivalent focal lengths). Often critical is the improved low light AF performance availed by a wide-aperture lens.

A narrow aperture's advantages are related to (often significantly) reduced lens element size, including smaller overall size, lighter weight, and lower cost. While those aspects are unavoidable, they fortunately do not strongly impact this lens.

Wide apertures are not always needed, especially in ultra-wide-angle focal lengths.

Motion blur is caused by subject details crossing over imaging sensor pixels during the exposure. Although this lens can be used with a close subject rendered large in the frame, lenses such as this one are often used at normal (or even long) subject distances. The low magnification means those subjects' details more readily stay in their pixels, enabling the longer exposures required to compensate for the narrower aperture to still deliver sharp results, free of subject or camera motion blur.

Many of the uses for this lens mandate a narrower aperture, such as f/8 or f/11, to keep everything in the frame sharp, and photographers concentrating on landscape, architecture, real estate, etc. may seldom use the f/1.4 option.

Still, the f/1.4 aperture is an extremely valuable feature of this lens. Those photographing moving subjects, such as at sports events or under the night sky where light levels are so low that the earth's rotation becomes a source of camera motion, will appreciate this lens's capabilities.

It is hard to diffusely blur the background with the low magnification provided by an ultra-wide-angle lens. Such lenses render the background details small in size, keeping the background subjects more recognizable (and potentially distracting). Still, this lens's short minimum focus distance and wide aperture can make a strong blur happen, adding artistic advantages to this lens's list of highly-desired features.

These examples illustrate the maximum blur this lens can create:

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What background blur advantage does f/1.4 provide over your widest 20mm lens's max aperture? Also, consider the ISO difference. If your widest 20mm lens opens to f/2.8, a bright Milky Way exposure may require ISO 12800 instead of ISO 3200 at f/1.4.

Only a 1/60 second shutter speed (twice the framerate) is needed for 30 fps video capture, and wide apertures are not often required to get 1/60 in normally encountered ambient lighting.

If shooting in direct sunlight at f/1.4, expect to need a 1/8000 sec or faster shutter speed at ISO 100 to avoid over-exposure. Positive is that there is little action that a 1/8000 sec shutter speed cannot stop, but if the subject has bright or reflective colors, even 1/8000 might not be fast enough to avoid blown highlights. Some cameras have an extended ISO setting as low as 50 that can optionally be used in this situation (though the dynamic range may be impacted). Optimal is to use a camera offering shutter speeds faster than 1/8000. Using a neutral density filter is another good solution to retaining the use of /1.4 under direct sunlight when the shutter limitation is exceeded. Stopping down (narrowing) the aperture is always an option for preventing over-exposure, though stopping down negates the value of the wide f/1.4 aperture and loses the subject-isolating shallow depth of field.

This lens features an aperture ring, permitting a manually selected aperture. The camera controls the aperture setting with the ring in the A (Auto) position. All other settings electronically force the aperture to the chosen opening. A 2-position switch on the bottom left side of the lens toggles the aperture ring between 1/3 stop clicks and smooth, quiet, non-clicked adjustments, ideal for video recording.

Aside from a slightly more complicated design, I find inadvertent aperture changes the primary disadvantage of an aperture ring (especially when photographing in the dark). In previous reviews, I mentioned that a lock for the ring would eliminate that issue, and this lens gets an iris lock switch that prevents switching between A and the manual selection range while allowing changes within the manual range.

Image Stabilization

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The shorter the focal length, the smaller subject details (captured at the same distance) are rendered, and the less still the camera must be held to avoid subject details crossing imaging sensor pixels, the source of motion blur. Still, image stabilization remains a valuable feature in any lens. Sigma has omitted image stabilization in their recent wide-aperture prime lenses, and not surprising is that the Sigma 20mm F1.4 DG DN Art Lens also lacks this feature.

Sony addresses that omission with Steady Shot IBIS (In-Body Image Stabilization) in their mirrorless cameras. In addition to reducing camera shake, the stabilized imaging sensor provides a still viewfinder image, enabling careful composition. Furthermore, sensor-based AF takes advantage of the stabilized view for improved accuracy.

With no IS switch on the lens, the camera menu must be used to enable or disable IBIS or check the current settings. This extra step is a slight impediment to working quickly, going from tripod mounted to handholding, for example.

Image Quality

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Especially from a contrast and resolution (sharpness) standpoint, the Sigma 20mm F1.4 DG DN Art Lens is a remarkably high-performing lens.

At ultra-wide-angle focal lengths, using an f/1.4 aperture usually involves sacrificing sharpness more than I prefer. That is not the case with the two lenses tested.

The Sigma 20mm F1.4 DG DN Art Lens is extremely sharp from full-frame corner to corner at f/1.4. Lenses usually become sharper as they are stopped down one or two stops from their wide-open apertures, but this lens shows only a slight improvement at f/2. However, little improvement is needed, and this lens is exceptionally sharp at f/2.

Often, subjects are not placed in the center of a composition. In the periphery of the image circle, where light rays are refracted to a stronger angle than in the center, lenses typically show decreased sharpness. Again, this lens shows itself to be exceptional in the test chart results (more to come in this regard), showing primarily only the impact of normal peripheral shading.

Often, it is helpful to assess a new lens by comparing it to the previous one. In this case, the new lens is a massive upgrade from the old. The Sigma predecessor is the only other 20mm f/1.4 lens to compare, but 20 DG DN also performs better than most 24mm f/1.4 lenses.

The resolution chart is brutal/merciless on image quality, so let's take the testing outdoors, next looking at a series of center-of-the-frame 100% resolution crop examples. These images were captured in RAW format using a Sony Alpha 1 and processed in Capture One using the Natural Clarity method. The sharpening amount was 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 for your evaluations. The f/2 examples show a slight improvement over the f/1.4 images, but the f/1.4 results are quite sharp.

Immediately after shooting the resolution test chart, I took this lens to photograph the Milky Way, where it again delivered impressive results from corner to corner (a corner example is shared later in the review). However, further testing revealed new information.

Next, we'll look at a series of comparisons showing 100% resolution extreme top right and then top left corner crops captured and processed identically to the above center-of-the-frame images. The lens was manually focused in the corner of the frame to capture these images.

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Samples taken from the outer extreme of the image circle, full-frame corners, can be counted on to show a lens's weakest performance, and midrange distance results show mild softness in the extreme corners. I could not produce sharper results than those shared above, even after retesting, including from two copies of this lens model.

The Sigma 20mm F1.4 DG DN Art Lens optical design is optimized for infinity focus distance, ideally suited for astrophotography, landscapes, and architecture. At shorter focus distances, especially at max and near max apertures, 'character' may be observed in the image circle periphery.

Does corner sharpness matter? Sometimes it does, sometimes it doesn't.

As jsut mentioned, astrophotography, landscape, and architecture photography are photographic disciplines that typically require sharp corners. However, those scenarios usually require apertures narrower than f/5.6. When shooting at the widest apertures, depth of field is often shallow, and the plane of sharp focus less frequently includes details showing in a corner, making corner sharpness less important.

When shooting nightscapes, wide apertures and tack-sharp corners are mandatory. For that use, this lens is the best available.

This lens does not exhibit focus shift, the plane of sharp focus moving forward or backward as the aperture is narrowed (residual spherical aberration or RSA).

A lens is expected to show peripheral shading at the widest aperture settings when used on a camera that utilizes its entire image circle. Wide-angle, ultra-wide aperture lenses tend to show strong peripheral shading wide open, and this lens's 3 stops of f/1.4 corner shading are noticeable, including in the above sample images. However, this amount is not strong from a comparative perspective.

Stopping down to f/2 drops about a stop of shading to just over 2 stops, and f/2.8 takes that number down to 2 stops. A slight improvement at f/4 ends the shading decline. The about 2 stops of shading still present at f/16 are relatively strong.

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 corner shading showing at f/1.4 may be visible in select images, primarily those with a solid color (such as a blue sky) in the corners.

One-stop of shading is often used as the visibility number, though subject details provide a widely varying amount of vignetting discernibility. Vignetting is correctable during post-processing with increased noise in the brightened areas the penalty, or it can be embraced, using the effect to draw the viewer's eye to the center of the frame. Study the pattern shown in our vignetting test tool to determine how your images will be affected.

Lateral (or transverse) CA (Chromatic Aberration) refers to the unequal magnification of all colors in the spectrum. 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 most significant amount as this is where the most significant 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. However, it is always better to avoid this aberration in the first place.

Color misalignment can be seen in the site's image quality tool, but let's also look at a worst-case example. The image below is a 100% crop from the extreme top left corner of a Sony a1 frame showing diagonal black and white lines.

Only black and white colors should be present in these images, with the additional colors indicating only a slight presence of lateral CA. This is excellent performance.

A relatively common lens aberration is axial (longitudinal, bokeh) CA, which causes non-coinciding focal planes of the various wavelengths of light. 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 observe. Axial CA remains somewhat persistent when stopping down, with the color misalignment effect increasing with defocusing. 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.

The examples below look at the defocused specular highlights' fringing colors in the foreground vs. the background. The lens has introduced any fringing color differences from the neutrally-colored subjects.

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The color blur is rather strong (though not unusual) at f/1.4 and slowly improves as the aperture is narrowed.

Bright light reflecting off lens elements' surfaces may cause flare and ghosting, resulting in reduced contrast and sometimes interesting, usually destructive visual artifacts. The shape, intensity, and position of the flare and ghosting effects in an image are variable, dependent on the position and nature of the light source (or sources), selected aperture, shape of the aperture blades, and quantity and quality of the lens elements and their coatings. Additionally, flare and ghosting can impact AF performance.

This lens features Sigma's Super Multi-Layer Coating that controls flare nicely. Only tiny flare effects are seen even at narrow apertures in our standard sun in the corner of the frame flare test, reflecting excellent performance.

Flare effects can be embraced or avoided, or removal can be attempted. Unfortunately, removal is sometimes challenging, and in some cases, flare effects can destroy image quality. Thus, high flare resistance is a welcomed trait of this lens.

Two lens aberrations are particularly evident in 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). This aberration can produce stars appearing to have wings. 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 a1 image captured at f/1.4.

Do you see how nicely sharp and round those stars are rendered? That corner performance is outstanding and differentiating.

They told us so: "Optimized for astrophotography, the lens offers extremely well-controlled sagittal coma flare and limits ghosting." [Sigma]

This lens has a modest amount of barrel distortion. While this amount of distortion will seldom be noticed, it will slightly fill out the Milky Way in the composition.

Most modern lenses have correction profiles available (including in-camera), and distortion can easily be removed using these. Still, geometric distortion correction requires stretching which is detrimental to image quality.

As seen earlier in the review, it is easy to illustrate the strongest blur a lens can create, and wide-angle lenses are inherently disadvantaged in this regard. Here are some f/8 (for diaphragm blade interaction) examples.

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The first example, a 100% resolution crop, shows rather smoothly filled defocused highlights, with the 11 aperture blades keeping the shape circular. The second set of examples shows a full image reduced in size and looking nice.

Except for a small number of specialty lenses, the wide aperture bokeh in the frame's corner 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 frame's corner, the shape is not round. That is the shape we're looking at here.

Shown below are upper-left quadrant crops reduced in size.

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As the aperture narrows, the entrance pupil size is reduced, and the mechanical vignetting absolves, making the shapes rounder.

An 11-blade count diaphragm will create 22-point sunstars (diffraction spikes) from point light sources captured with a narrow aperture. In general, the more a lens diaphragm is stopped down, the larger and better-shaped the sunstars tend to be. Wide aperture lenses tend to have an advantage in this regard, and this lens is capable of producing outstanding star shapes, as illustrated below.

The example above was captured at f/16.

The Sigma 20mm F1.4 DG DN Art Lens design includes two SLD and three aspherical elements, including Sigma's largest ever double-sided aspherical glass element.

This lens does not turn in a perfect score in regards to geometric distortion, peripheral shading, color blur, and extreme corner image quality at mid distances. But, the Sigma 20mm f/1.4 DG DN Art Lens otherwise delivers excellent image quality and perhaps the best night sky image quality available.

Focusing

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Like many of its siblings, the Sigma 20mm f/1.4 DG DN Art Lens utilizes a stepping motor for AF. This lens quietly internally focuses with good speed.

Keep in mind that while the focus speed is relatively fast, Sony cameras' normal defocusing prior to focusing increases lock time significantly in AF-S (single shot) mode.

FTM (Full Time Manual) focusing is supported in Sony's DMF (Direct Manual Focus) mode with the shutter release half-pressed or the AF-ON button pressed.

Sigma provides a customizable AF hold button on this lens. While in continuous focus mode, this button can be pressed to lock focus at the currently selected focus distance, facilitating a focus and recompose technique. This button also acts as a custom button and can be programmed to another function using the camera's menu.

Normal is for the scene to change size in the frame (sometimes significantly) as the focus is pulled from one extent to the other. This effect is focus breathing, a change in focal length resulting from a change in focus distance. Focus breathing impacts photographers intending to use focus stacking techniques, videographers pulling focus (without movement to camouflage the effect), and anyone critically framing while adjusting focus.

This lens produces a significant change in subject size through a full extent focus distance adjustment.

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The rubber-coated, sharp-ribbed focus ring is large and, being raised slightly from the lens barrel behind it, is easy to find. This ring rotates smoothly, has an optimal amount of resistance, and the long 1070° of slow rotation MF adjusts focusing at a rate that facilitates precise manual focusing even at close distances. Turn the ring fast to go the full extent range in about 200° of rotation. I'd prefer the speed change to occur at a faster rotation to facilitate faster MF fine-tuning.

This lens has an AF/MF switch, a feature that has gone missing on many modern lenses and one that I appreciate greatly.

In addition, this lens has a unique Manual Focus Lock (MFL) switch. Sometimes, such as when photographing the night sky, you want to ensure that the focus ring does not move. No longer is gaffer tape needed for this function. Via a switch, this lens provides the focus distance lock function when in MF mode.

With a minimum focus distance of 9.1" (230mm), this lens has a relatively low 0.16x maximum magnification spec.

Model	Min Focus Distance "(mm)		Max Magnification
Canon RF 24mm F1.8 Macro IS STM Lens	5.5	(140)	0.50x
Sigma 20mm F1.4 DG DN Art Lens	9.1	(230)	0.16x
Sigma 20mm f/1.4 DG HSM Art Lens	10.9	(277)	0.14x
Sigma 20mm F2 DG DN Contemporary Lens	8.7	(220)	0.15x
Sigma 24mm F1.4 DG DN Art Lens	9.8	(250)	0.14x
Sigma 24mm f/1.4 DG HSM Art Lens	9.8	(250)	0.19x
Sigma 24mm F2 DG DN Contemporary Lens	9.6	(245)	0.15x
Sigma 24mm F3.5 DG DN Contemporary Lens	4.3	(108)	0.50x
Sony FE 20mm F1.8 G Lens	7.1	(180)	0.20x
Sony FE 24mm F1.4 GM Lens	9.4	(240)	0.17x
Sony FE 24mm F2.8 G Lens	7.1	(180)	0.19x
Sony FE 28mm F2 Lens	11.4	(290)	0.13x
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

A subject measuring approximately 7.1 x 4.7" (180 x 120mm) fills a full-frame imaging sensor at this lens's minimum MF distance.

While this lens produces sharp center of the frame details at minimum focus distance at f/1.4, expect the image periphery to be soft due to field curvature. F/11 brings on increased depth of field that provides significant improvement in corner image quality.

With the lens and possibly hood lengths taking a bite out of the minimum focus distance, there is not much working distance remaining — about 1.1" (23mm) from the frontmost hood petal. With the hood removed, about 2.5" (64mm) of working distance is available, still a challenge avoid shadows.

The USPS love stamps shared above have an image area that measures 1.05 x 0.77" (26.67 x 19.558mm), and the overall individual stamp size is 1.19 x 0.91" (30.226 x 23.114mm).

Need a shorter minimum focus distance and higher magnification? Mount an extension tube behind this lens to significantly decrease and increase those respective numbers (expect only short tubes to be usable). Extension tubes are hollow lens barrels that shift a lens farther from the camera, allowing shorter focusing distances at the expense of long-distance focusing. Electronic connections in extension tubes permit the lens and camera to communicate and function normally. As of review time, Sigma does not publish extension tube specs or manufacture these items, but third-party Sony-compatible extension tubes are available.

This lens is not compatible with Sigma teleconverters.

Build Quality & Features

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Sigma's premium grade Art lenses all feature great build quality, physical performance, and aesthetics.

"The robust body is built from a combination of aluminum and Thermally Stable Composite (TSC), giving it a sleek finish" [Sigma]

"TSC is a state-of-the-art polycarbonate that is designed to be both lightweight and extremely durable, and its chemical makeup means it doesn't shrink or expand with changing temperatures. This material is so high-quality that we're also incorporating it into our Art and Sports lenses to provide lightness and thermal consistency." [Sigma]

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This is a fixed-size lens, with, primarily, a consistent diameter enhancing comfort during use. The front of this lens flares outward to a significantly wider diameter, going from 3.01 to 4.66" (76.5mm to 87.8mm).

While this diameter change does not appear necessary from an optical standpoint, there are two good reasons for this physical design attribute. One reason is to permit threaded front filters without strong vignetting (more later), and the second reason is to accommodate a lens heater, eliminating condensation during astrophotography.

"A new Lens Heater Retainer keeps this useful astrophotography weather accessory firmly in place while in use." [Sigma] The heater, used to avoid internal condensation when temperatures drop, wraps around the barrel with the raised area preventing it from sliding forward and blocking the optical path.

About 1/3 of the space between the focus ring and the aperture ring is ribbed for improved grip. 3/4 of the aperture ring is ribbed, and when this ring is locked, these grooves also increase grip, useful especially for mounting and unmounting the lens.

About 1/3 of the space between the focus ring and the aperture ring is ribbed for improved grip. 3/4 of the aperture ring is ribbed, and when this ring is locked, these grooves also increase grip, useful especially for mounting and unmounting the lens.

All four switches are 2-position types that firmly click into their positions, with a white background displayed when the enabled position is selected. Two of the switches, along with the autofocus lock button, are mounted on a low-profile switch bank.

This lens has weather sealing, including a rear mount gasket.

Water- and oil-repellent coating is applied to the front element to repel dust and water and facilitate cleaning.

For a 20mm lens having an f/1.4 aperture, this one is relatively compact and lightweight, considerably more so than its predecessor.

Model	Weight oz(g)		Dimensions w/o Hood "(mm)		Filter	Year
Canon RF 24mm F1.8 Macro IS STM Lens	9.5	(270)	2.9 x 2.5	(74.4 x 63.1)	52	2022
Sigma 20mm F1.4 DG DN Art Lens	22.2	(630)	3.5 x 4.5	(87.8 x 113.2)	82	2022
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 F2 DG DN Contemporary Lens	13.1	(370)	2.8 x 2.9	(70.0 x 72.4)	62	2022
Sigma 24mm F1.4 DG DN Art Lens	18.0	(510)	3.0 x 3.8	(75.7 x 97.5)	72	2022
Sigma 24mm f/1.4 DG HSM Art Lens	23.5	(665)	3.3 x 3.6	(85.0 x 90.2)	77	2015
Sigma 24mm F2 DG DN Contemporary Lens	12.9	(365)	2.8 x 2.8	(70.0 x 72.0)	62	2021
Sigma 24mm F3.5 DG DN Contemporary Lens	7.9	(225)	2.5 x 2.0	(64.0 x 50.8)	55	2020
Sony FE 20mm F1.8 G Lens	13.2	(373)	2.9 x 3.3	(73.5 x 84.7)	67	2020
Sony FE 24mm F1.4 GM Lens	15.7	(445)	3.0 x 3.6	(75.4 x 92.4)	67	2018
Sony FE 24mm F2.8 G Lens	5.7	(162)	2.7 x 1.8	(68.0 x 45.0)	49	2021
Sony FE 28mm F2 Lens	7.1	(200)	2.5 x 2.4	(64.0 x 59.9)	49	2015
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

For many more comparisons, review the complete Sigma 20mm F1.4 DG DN Art Lens Specifications using the site's lens specifications tool.

The joints of my fingers modestly impact the barrel of this lens when tightly gripping the Sony a1.

Here is a visual comparison:

Positioned above from left to right are the following Sigma Art lenses:

Sigma 20mm F1.4 DG DN Art Lens
Sigma 24mm F1.4 DG DN Art Lens
Sigma 35mm f/1.4 DG DN Art Lens
Sigma 85mm f/1.4 DG DN Art Lens

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

Let's put a pair of focal length matching Sony lenses next to the Sigma Art lenses.

Positioned above from left to right are the following lenses:

Sigma 20mm F1.4 DG DN Art Lens
Sony FE 20mm F1.8 G Lens
Sigma 24mm F1.4 DG DN Art Lens
Sony FE 24mm F1.4 GM Lens

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

Use the site's product image comparison tool to visually compare the Sigma 20mm F1.4 DG DN Art Lens to other lenses.

This lens's predecessor had a bulbous front lens element that precluded the use of front filters.

"State-of-the-art optical design and the large, high-precision double-sided aspheric glass front element made it possible to add a front filter thread without any compromises regarding optical performance or size." [Sigma]

This lens seems larger than necessary at the front, but the filter accommodation provides logic for that design.

While the 82mm thread diameter is large and 82mm filters are expensive, this is a common filter size. Also, most other filter thread sizes can use a step-up filter adapter ring to use 82mm filters.

A standard-thickness circular polarizer filter will slightly increase peripheral shading. Therefore, a slim model such as the Breakthrough Photography X4 is highly recommended.

Additionally, a rear drop-in filter holder is provided.

A GP-11 plastic stencil is provided to aid in cutting gel filters.

Sigma includes the lens build quality matching LH782-01 lens hood in the box. This is a rather solid petal-shaped plastic hood with a ribbed interior designed to avoid reflections. An advantage of this hood shape is easier alignment (simply learn the small petal to the top installation orientation), though a round-shaped hood better enables the lens to stand on its hood. This hood offers substantial protection from impact and bright light. A release button makes installation and removal easy with the rubberized rear portion of the hood and a thin ribbed section in front of it enhancing grip.

Sigma provides my favorite lens packing material in the box — a nice zippered padded nylon case. This case features a neckstrap but not a belt loop.

Price, Value, Compatibility

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Competing strongly with any wide-angle prime lens on the market, including from optical and build quality standpoints, the Sigma 20mm f/1.4 DG DN Art Lens is a great value. Priced similar to Sony's also excellent but 2/3-stop slower f/1.8 alternative also shows the Sigma 20mm f/1.4 DG DN Art Lens a strong value.

The "DG" refers to full-frame camera compatibility, and the "DN" indicates that this lens was designed for short-flange mirrorless cameras. The Sigma 20mm F1.4 DG DN Art Lens is compatible with all Sony E-mount cameras, including APS-C sensor format models, and it is also available in the L mount (Sigma, Panasonic, Leica).

Made in Japan, each Art lens is tested with Sigma's proprietary MTF measuring system, ensuring a quality product. In regards to the Sony E-mount version of this lens, Sigma develops, manufactures, and sells lenses based on the specifications of E-mount, disclosed by Sony Corporation under license agreement. Sigma provides a 1-year limited warranty, and Sigma USA provides a limited 3-year warranty extension.

One of the reviewed Sigma 20mm F1.4 DG DN Art Lenses was on loan from Sigma Corporation of America, and the other tested lens was online retail acquired.

Alternatives

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The first lens I wanted to compare the Sigma 20mm F1.4 DG DN Art Lens to is the Sony FE 24mm F1.4 GM Lens. While this lens does not have the same focal length, I regard the FE 24 F1.4 as the best performing f/1.4 astrophotography lens to date. Thus, it was interesting to put the substantially less expensive Sigma lens up against the best available option.

The image quality comparison shows the two lenses performing about the same. The Sony lens may have a tiny advantage in the center of the frame at f/1.4, but both perform extremely well. While neither lens has strong geometric distortion, the Sigma lens's slight barrel distortion appears noticeably different than the Sony lens's slight pincushion distortion.

The Sigma 20mm F1.4 DG DN Art Lens vs. Sony FE 24mm F1.4 GM Lens comparison shows the Sigma lens modestly larger and heavier. The Sony lens uses 67mm filters vs. 82mm. The Sigma lens has an MF lock and aperture ring lock switches. Again, the Sigma lens is considerably less expensive. It is hard to go wrong with either of these lenses.

The Sigma 24mm F1.4 DG DN Art Lens was released at the same time as the 20, and with only a modestly narrower angle of view, this lens is worthy of comparison.

The image quality comparison shows the 20mm lens noticeably sharper throughout the frame at f/1.4 and still sharper at f/2.8. The 20mm lens has slightly stronger barrel distortion and less lateral CA.

The Sigma 20mm F1.4 DG DN Art Lens vs. Sigma 24mm F1.4 DG DN Art Lens comparison shows the 20mm lens measuring larger and weighing 4.2 oz (120g) more. Along with the larger size comes 82mm filter threads vs. 72mm. The 20mm lens has a slightly higher maximum magnification, 0.16x vs. 0.14x, and is priced $100.00 higher at review time.

As mentioned at the beginning of this review, Sigma has another 20mm f/1.4 lens, the Sigma 20mm f/1.4 DG HSM Art Lens. As also mentioned earlier in this review, the new lens delivers far sharper image quality. The DN lens also shows considerably less flaring.

The Sigma 20mm F1.4 DG DN Art Lens vs. Sigma 20mm f/1.4 DG HSM Art Lens comparison shows the HSM lens larger and a painful 50% heavier. The HSM lens has two fewer aperture blades, 9 vs. 11, and does not have front filter threads. The DN lens has a higher maximum magnification, 0.16x vs. 0.14x. The two lenses have the same price, making the DN lens the easy choice if the needed lens mount version is available.

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Summary

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I'm excited about the Sigma 20mm F1.4 DG DN Art Lens — I plan to purchase it for my kit, where it will serve as a key member of the landscape and nightscape team.

While the extreme corners are not tack sharp at mid distances, but otherwise, there are few lenses at any focal length that deliver f/1.4 image quality as sharp as this one does.

Art lens build quality, physical performance, and aesthetics are additional strong attractions to this lens. So is this lens's modest price.