Tamron brought smiles to the world when they introduced a pair of record-setting lenses, the Tamron 35mm f/1.8 Di VC USD Lens and the very similar Tamron 45mm f/1.8 Di VC USD Lens, with both sharing the record for being the widest aperture image stabilized lenses available at the time of their introduction.
Tamron had previously introduced the world’s first image stabilized 24-70mm lens (the 24-70mm f/2.8 Di VC USD) and the world’s widest-angle image stabilized lens (15-30mm f/2.8 Di VC USD), so the introduction of the world’s widest-aperture image stabilized lenses should come as no surprise.
Or maybe we should be surprised as until now, Tamron's widest aperture and widest angle full frame prime lens was the Tamron 90mm f/2.8 Di VC USD Macro Lens and there are only three primes total in Tamron's current lens catalog with all three of those being macro lenses.
The Tamron 35mm and 45mm f/1.8 VC lenses differ by little more than one digit in their names and therefore, this review is going to sound familiar if you have read the 45 f/1.8 VC lens review. These lenses are so similar that ... I'm embarrassed to admit ... in haste to take advantage of clear skies one afternoon, I grabbed the wrong lens for a few hours of outdoor testing. I was so focused on setting up the tests properly that I failed to notice that I had the wrong focal length lens mounted on the camera until I saw the 35 still on the shelf when I finished. Aside from the shorter lens barrel and the 35mm printed in a small font, the 35 looks exactly like the 45, right down to the lens hood model.
Though the product identification perhaps needs to be improved, the similarity between these lenses is a good thing. Like the 45, the Tamron 35mm f/1.8 Di VC USD Lens has a brand new, sleek-looking modern lens design that includes a metal barrel, a very useful focal length, very good image quality and a great-value price that will bring smiles to photographers and their clients alike.
Seemingly unusual is that Tamron chose to start a new line of prime lenses with two entries having focal lengths so close together. Just by looking at these lenses, it is not hard to determine that design and build synergies were involved. Why create only one new lens when two can be developed with little additional effort? Having two lenses simultaneously introduced also helps establish a line faster, avoiding the appearance of a one-off product.
Regardless, focal length matters. Make it a primary consideration for your lens selection. The moderately wide angle 35mm focal length is a very popular one with good reason: this angle of view has a vast range of uses, especially when paired with a wide aperture.
I often press whatever lens I'm reviewing at the time into the around-the-house, general purpose lens role. I'm always happy when that lens covers 35mm (there are a lot of them and a lot of relatively new ones), as I know it will work well for a wide range of the most common needs I encounter. The 35mm focal length 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. As a prime lens, it is often not difficult to sneaker zoom to the right distance to get the ideal subject framing.
The 35mm focal length has long been a first-choice for photojournalists. Wedding photographers, who work in some of the worst lighting venues to be found, also frequently use 35mm lenses. Portrait photographers like the 35mm focal length for full to mid-body portraits and for group portraits. Landscape photographers have plenty of use for the 35mm focal length.
Sports photographers able to get close to their subjects (such as basketball shot from over or under the net) or wanting to capture a wider/environmental view of their events appreciate this focal length. The angle of view invited by 35mm will make action figures large in the frame. Parents love 35mm lenses for capturing their indoor events and most pets will let you get close enough to capture a nice perspective with such a lens. 35mm is popular with videographers, especially for creating documentaries. Many medium and large products are ideally captured at 35mm.
The full list of 35mm uses is huge and limited only by the extents of our imaginations.
On an ASP-C/1.6x sensor format body, the 35mm focal length provides an angle of view similar to a 56mm lens on a full frame sensor format body. The 56mm angle of view is close enough to 50mm to be used for all applications this extremely popular "normal" focal length is used for. Those uses coincide with most uses of the 35mm focal length with slightly tighter framing or slightly longer perspective for the same framing being the difference.
One of the advantages that a prime lens typically has over a zoom counterpart is a wide aperture. At review time, the Sigma 24-35mm f/2 Art Lens and the APS-C-only Sigma 18-35mm f/1.8 Art Lens are the only zoom lenses with an aperture wider than f/2.8. The Tamron 35 f/1.8 VC holds a 1/3 stop advantage over these zooms (and has the added versatility of VC), but it is one of the slower 35mm prime lenses available.
Still, an f/1.8 aperture is very wide, allowing action to be stopped under low light levels and the camera to be handheld in even lower light levels. It also provides a bright viewfinder and provides a significant amount of light to the AF system, activating the high-precision mode in some cameras. I especially like the wide aperture's shallow depth of field capability. Though a wide angle lens is more challenged to create a diffusely blurred background than a telephoto lens, this lens, especially when used at a close focus distance, has the shallow depth of field capability to remove background distractions. Here is an aperture walkthrough:
Nice was that the praying mantis showed up, giving me something to focus on. These uncropped (reduced size) full frame captures used shutter speed changes matching the aperture changes. Obvious is that the background blur at f/1.8 is potentially strong.
While the f/1.8 aperture alone is great for low light use, vibration compensation greatly extends the versatility of this lens. When you need to leave the tripod behind, VC is there for you.
Perhaps most important is that VC allows handholding of the camera in extremely low light situations with still subjects (or permits motion blurring of subjects with sharp surroundings). Also valuable is that VC allows handholding in medium and low light levels when more depth of field is needed, allowing narrower aperture use without a tripod. When using a circular polarizer filter with narrow apertures (typical for landscapes and cityscapes), VC can be helpful even under a full sun.
VC is useful for stabilizing the viewfinder, aiding in optimal composition. VC is also very useful for video recording, creating pleasant, easy-to-watch movies.
This VC implementation is very quiet with a light clicking being audible on startup and shutdown and with only a very faint hum heard while activated. In this lens, VC activation does not cause the viewfinder image to jump and it makes a very noticeable difference in the stability of the image in the viewfinder, with the scene becoming very still. With a camera held very still and after roughly 10 seconds of VC activation, the subject framing begins to shift slightly in the viewfinder. Overall, this is a nicely implemented stabilization system.
How well VC actually keeps the image still is the most important aspect of such a system. Tamron does not list a number of stops rating for this VC implementation, and your experience will vary depending on your circumstances, your capabilities, the camera used and the pixel density of its sensor. I have sharp handheld images at shutter speeds as long as .5 seconds, but my slowest set with a very high sharpness percentage was 1/6 sec., for a roughly 3 2/3 stops of assistance for me. That is a very nice amount of assistance. Nearly four stops of added handholding capability is a huge advantage.
I know, many of you jumped right to this subheading. The sharpness (contrast and resolution) of a lens is paramount to it being welcomed into our kits.
With a wide open aperture, center of the frame results are reasonably sharp at f/1.8. A nice improvement in center sharpness is realized at only 1/3 stop of closure with another bump in sharpness seen at f/2.8 where this lens is really sharp. Improvement at f/4 is minor and negligible at f/5.6. The only reason to stop down further than f/4 (and probably f/2.8), from a center-of-the-frame perspective, is to gain DOF.
It is typical for corner sharpness in wide angle lenses to trail the performance found in the center of the frame. In that regard, this lens turns in above-average performance with full frame f/1.8 corners that are not too dissimilar from the center. A noticeable bump in corner sharpness is seen at f/2.8, with clearing vignetting being a primary driver of that visual difference. Sharpness at f/2.8 is very good and slightly better yet at f/4 with little improvement seen with narrower apertures.
Even on a high density imaging sensor DSLR, such as the 4.1µm pixel pitch found in the Canon EOS 5Ds R, this lens delivers good image sharpness across the frame at f/2 (stopping down 1/3 stop is worth the improvement in the center of the frame), very good image quality at f/2.8 and impressive image quality at f/4.
The following comparison shows 100% resolution crops taken from the center of the frame of images captured on a clear day in RAW format using the Canon EOS 5Ds R. These images were processed in Canon's DPP using the "Standard" Picture Style with sharpness adjusted down to "1". The exposures used are equivalent across all examples shown here (aperture changes are offset be equivalent shutter speed changes).
When making comparisons, depth of field is at play, so choose the sharpest wider aperture details to compare against the narrower aperture details. Add a slight amount of sharpening and contrast and the f/1.8 image is ready for use. Mouse over the f/2 label and see why I advise using f/2 over f/1.8 when sharpness and contrast are paramount.
Mouse over (or click/tap) on the f/2.8 and f/4.0 labels under the image and look at the very impressive results delivered by this lens stopped down. I don't see a reason to go narrower than f/4 in regards to center of the frame image sharpness and the results at f/4 are extremely sharp.
Next, look at a pair of 100% resolution crops taken from the absolute corners of EOS 5Ds R images captured and processed similarly as described above. Crops from the absolute top left of the frame are presented in the first comparison example below.
Obvious is the vignetting resolving at narrower apertures and the corner details really popping into sharpness at f/4. Moving to the absolute bottom left of the frame shows similar results.
Critically sharp corners at f/1.8 are not important to everyone and/or every situation. Keeping everything in perspective, this lens is reasonably sharp across the frame at f/1.8 and becomes impressive when stopped down. Almost as impressive as this lens’ f/4 corner sharpness is the fact that a bumblebee remained on a single flower for the duration of this test.
As expected, some vignetting is present in full frame corners at f/1.8 with about 2 stops being the amount of darkening visible. By f/2.8, peripheral shading has decreased to about 1 stop where it is barely noticeable. From f/4 through f/16, about .7 stops of shading remains in full frame corners.
Those using ASP-C format sensor cameras will notice little or no corner darkening even at f/1.8 (roughly .7 stops) and by f/2.8, only an unnoticeable .3 stops remains.
Some lateral/transverse CA (Chromatic Aberration) shows in the peripheral full frame image circle. Here is an EOS 5Ds R corner showing the edge of a house roof.
The only colors in this image should be blue sky and various shade of grey (white fascia to black shingles with shading). Lateral CA is generally easy to correct in software.
Common in wide angle, wide aperture primes including this one and more challenging to correct than lateral CA is spherical and axial/longitudinal CA. Some modest CA will show in bokeh and expect to see some purple fringing in high contrast subjects captured at wide apertures. Chrome is a subject that readily makes purple fringing apparent as shown in this f/1.8 example.
Coma (not to be confused with CA) is generally recognized by sharp detail contrast towards the center of an image and long, soft contrast transition toward the image periphery. Coma is most visible in wide aperture corners and the pin-point stars in the night sky are the subject that illuminates this aberration most easily for me. The following example, showing a 100% crop from a top right full frame 5Ds R corner of a night sky image (under a full moon), shows that this lens indeed has modest amount of coma.
Prime lenses generally perform well in regard to distortion and the Tamron 35 VC is no exception. This lens has a barely perceptible amount of barrel distortion. It was not easy to see this, even with a straight line running along the edge of the frame. Here is the edge of a window running across the edge of an entire full frame image (reduced of course):
The window frame line running immediately against the edge of the frame is ruthless for showing distortion. Unless your straight-line subject is similarly positioned, you will not likely notice this lens' curving effect. If the curve shown above bothers you, don't try the same test with the widest and longest focal lengths of your normal zoom lens.
As shown earlier in the review, this lens can blur the background strongly. The quality of that blur, affectionately referred to as "bokeh", is mid-grade. It is not terrible, but it is not amazing either. Out of focus specular highlights do not have the smoothest centers as seen and I've run into some busy-appearing bokeh.
The first two examples are from near the center of f/5.6 images. The second two examples, taken from the same image, show blurred backlit dew hanging on grass in the yard. The third example, showing busy bokeh, is taken from roughly 70% into the image circle radius.
With a 9-blade aperture, each aperture blade intersection creates its own pair of star points with a point light source and a narrow aperture in use. Thus, 18-point stars are created by this lens.
The Tamron 35mm f/1.8 VC Lens shows a mild amount of flare effects at wide apertures with a clear sky sun in the corner of the frame. As the aperture narrows, flare will slowly become more apparent and show very noticeably at f/11 through f/16. This lens is an average performer in this regard.
In the end, we see the Tamron 35mm f/1.8 VC Lens turning in a range of performance across the image quality factors. If this lens were priced near $2,000, I would not be too excited at this point. However, at the price point of this lens even at its initial introduction price, the performance seen here is quite attractive.
As denoted by the "USD" in its name, the Tamron 35mm f/1.8 Di VC USD Lens utilizes a ring-type USD (Ultrasonic Drive) autofocus motor. This implementation is an inner focusing and floating system design that does not change the external lens size during focusing and permits FTM (Full Time Manual) focusing without a switch change.
The Tamron 35's autofocus speed is good. Notably, it is a bit faster than its 45 f/1.8 VC sibling. It is common for the camera to fine tune the 45's focus distance after the initial change, causing the overall focus lock time to increase slightly. I find there to be less fine tuning adjustment occurring with the 35 compared to the 45.
Going hand in hand with the image quality delivered by a lens is AF accuracy (unless using MF of course). Testing AF accuracy with this lens has driven me a bit crazy. Just when I was ready to declare it mostly very good, I would get a set of test results with the plane of sharp focus landing all over the place. Mostly, both the center and the peripheral AF points I tested worked reasonably well, but sometimes, the results were confusingly off the mark.
Here is a case in point. Using a tripod-mounted EOS 5Ds R, I placed the center-only selected AF point on this blue bird box. A series of images were then captured with each starting from a slightly defocused lens.
If all images were similarly blurred, AF Microadjustment would likely completely resolve the problem. Inconsistent focus on the other hand is problematic. Mostly this lens focused accurately for me, but ... not always.
With 101° of rotation, this lens' large, smooth, nicely damped, manual focus ring allows for reasonably precise manual focusing even at close distances.
Videographers should note that subjects change size noticeably during big focus pulls. As with most modern lenses, this lens' filter threads do not rotate.
Very remarkable is the Tamron 35mm f/1.8 VC Lens' MFD (Minimum Focus Distance) and related MM (Maximum Magnification). Focusing down to only 7.9" (200mm), this lens has an impressive 0.40x reproduction ratio. There are only two non-macro lenses currently in the site's database with higher MM specs. Those are the Nikon 80-400mm f/4.5-5.6D AF VR Nikkor Lens (not the newer AF-S version) with a 0.42x rating and the Canon EF 24-70mm f/4L IS USM Lens with a 0.70x rating.
Here is a comparison table showing the other 35mm prime lenses being left in the dust.
|Canon EF 35mm f/1.4L II USM Lens||11.0"||(280mm)||0.21x|
|Canon EF 35mm f/2 IS USM Lens||9.4"||(240mm)||0.24x|
|Canon EF 40mm f/2.8 STM Lens||11.8"||(300mm)||0.18x|
|Nikon 35mm f/1.4G AF-S Lens||11.8"||(300mm)||0.20x|
|Nikon 35mm f/1.8G AF-S Lens||9.8"||(250mm)||0.16x|
|Samyang 35mm f/1.4 US UMC Lens||11.8"||(300mm)|
|Sigma 35mm f/1.4 DG HSM Art Lens||11.8"||(300mm)||0.19x|
|Tamron 35mm f/1.8 Di VC USD Lens||7.9"||(200mm)||0.40x|
|Tamron 45mm f/1.8 Di VC USD Lens||11.4"||(290mm)||0.29x|
|Zeiss 35mm f/1.4 Distagon T* ZE Lens||11.8"||(300mm)||0.20x|
A high MM capability is a great benefit to a lens. Here is an example showing a roughly 3" (76mm) gerbera daisy captured at this lens' MFD using a full frame camera.
Ambient window lighting was used for this image. Even with the broad light source, the hood blocks enough light from reaching the subject to effect the results at this focus distance. I seldom recommend not using the hood, but ... when working near this lens' MFD, going hoodless may be a good idea.
Significant magnification increase can be enabled with the use of an extension tube. ETs permit the lens to focus to closer distances at the expense of long distance focusing. This lens is not compatible with extenders.
This lens is constructed the same as the 45mm f/1.8 VC. As I said about the 45, if you had not seen a picture of this lens prior and had not seen the manufacturer's name printed on it, Tamron would likely not have been the brand you guessed. This sharp-looking lens represents a completely new design for Tamron. From internals to the lens cap, every aspect of the lens is brand new.
Without a prior version of any lens similar to this one, the decision to start from scratch does not seem as if it would be difficult to make and a brand new lens model is a great introduction for a new design. With Tamron's aging lens appearance and with Sigma's modern Global Vision lens design being a hit, it is not surprising that Tamron decided to refresh its design.
The Tamron 35mm f/1.8 VC Lens has a very attractive, clean, modern appearance that features an aluminum alloy barrel. Here are the standard product image views of this lens.
This lens has a smooth overall design that, including from a diameter perspective, feels as good in hand as it appears to the eye. The nicely-sized manual focus ring is easy to find and use as are the nicely positioned switches (AF/MF and VC On/Off) that reside on a slightly-raised panel on the left side of the lens.
Both the switches and the panel are contoured to the lens barrel. The switches are very adequately sized with a sufficient amount of throw and a positive click to provide strong positional tactile feedback. There is no question about which position the switches are in.
Though this lens has a fixed overall size, the front lens elements do retract and extend during focusing as seen below.
This lens has moisture resistance incorporated into its design, including a lens mount gasket and seals in other locations. Tamron does not state that a front filter is required for complete sealing, but based on the lens design, a filter appears to be warranted for improved weather sealing. The front lens element is fluorine coated to repel water, fingerprints, and smudges for easier cleaning of the lens surface.
Though it comes across as somewhat large and heavy among the other 35mm f/1.8 and f/2 lenses, the size and weight do not seem inappropriate and this lens is a pleasure to use for extended durations.
Here are some comparisons:
|Model||Weight||Dimensions w/o Hood||Filter||Year|
|Canon EF 35mm f/1.4L II USM Lens||26.8 oz||(760g)||3.2 x 4.2"||(80.4 x 105.5mm)||72mm||2015|
|Canon EF 35mm f/2 IS USM Lens||11.8 oz||(335g)||3.1 x 2.5"||(77.9 x 62.6mm)||67mm||2012|
|Canon EF 40mm f/2.8 STM Lens||4.6 oz||(130g)||2.7 x 0.9"||(68.2 x 22.8mm)||52mm||2012|
|Nikon 35mm f/1.4G AF-S Lens||21.2 oz||(600g)||3.3 x 3.5"||(83.0 x 89.5mm)||67mm||2010|
|Nikon 35mm f/1.8G AF-S Lens||10.8 oz||(305g)||2.8 x 2.8"||(72.0 x 71.5mm)||58mm||2014|
|Samyang 35mm f/1.4 US UMC Lens||23.3 oz||(660g)||3.3 x 4.4"||(83.0 x 111.0mm)||77mm||2011|
|Sigma 35mm f/1.4 DG HSM Art Lens||23.5 oz||(665g)||3.0 x 3.7"||(77.0 x 94.0mm)||67mm||2012|
|Tamron 35mm f/1.8 Di VC USD Lens||16.9 oz||(479g)||3.2 x 3.2"||(80.4 x 81.3mm)||67mm||2015|
|Tamron 45mm f/1.8 Di VC USD Lens||19.2 oz||(544g)||3.2 x 3.6"||(80.4 x 91.4mm)||67mm||2015|
|Zeiss 35mm f/1.4 Distagon T* ZE Lens||29.7 oz||(840g)||3.1 x 3.9"||(78.0 x 99.3mm)||72mm||2010|
Adding the available 24mm, 28mm and 50mm prime lenses to this list would increase the number of lenses included very significantly. For many more comparisons, I'll direct you to the full Tamron 35mm f/1.8 Di VC USD Lens Specifications using the site's comparison tool.
Here is a visual comparison showing the 35 f/1.8 VC alongside three other popular lens models:
Positioned above from left to right in their fully retracted positions are the following lenses:
The same lenses are shown below with their lens hoods in place.
I wanted to have Sigma's closest competitor included in this comparison. Yes, the Sigma 35 Art lens has a 2/3 stop wider aperture, but it lacks the optical stabilization feature. And, it is similar in size and weight.
Note that even though the lens caps do not appear to be positioned at the same height, the lens mounts are leveled across the lenses. Not all lens caps have the same height.
Use the site's product image comparison tool to visually compare the Tamron 35mm f/1.8 Di VC USD Lens to many other lenses. The just-provided link is preloaded with another interesting comparison (showing the Canon and Nikon f/1.4 lenses in comparison).
The Tamron 35 f/1.8 VC accepts mid-size and moderately common 67mm filters.
The Tamron HF012 lens hood (the same model as included with the 45 f/1.8 VC) is included in the box. This a moderately-rigid, all-plastic lens hood with a ribbed interior that offers a nice amount of protection from both light and impact to the front element. Use it all the time, except perhaps when shooting at MFD.
Somewhat unusual is that the lens hood includes the words "Made in Japan" and the box says "Made in Japan", but the lens states "Designed in Japan". It seems that Tamron is stressing this lens' Japanese roots, but ... I suspect the wording will leave some wondering if the lens itself was actually "made" somewhere else.
The 35 VC's new ground-up design includes the lens caps. The front cap is very nice, featuring the center-and-side-pinch design that is now ubiquitous. The rear cap caught my attention even more, initially because it does not match up equally with the diameter of the Canon body cap (it is wider) and second, because it weighs noticeably more than the current Canon cap (though still weighing only 20g).
Tamron's wider, flaring cap design better connects with the lens mount weather sealing gasket, providing better protection to the gasket and better moisture protection to the lens when the cap is attached. You can see this fit in the product images earlier in review. The rear cap uses a double-wall design as seen in the image above.
Even the boxes are new. Tamron takes on a new face with freshly designed 35mm and 45mm f/1.8 VC Lens packaging.
No lens case is included in the box, but finding a case for a common lens form factor is not challenging. Lowepro's Lens Case line is very nice and affordable.
Tamron 35mm f/1.8 Di VC Lens has a medium-low price tag at launch time, matching the 45 f/1.8 VC lens' price. As with the 45, the 35's image quality and the quality of the lens itself make this price a very good value and a good value even if only used sparingly.
The Tamron 35mm f/1.8 Di VC USD Lens is available in Canon (reviewed), Nikon and Sony (no VC). My standard disclaimer: There are potential issues with third party lenses. Since Tamron reverse engineers (vs. licenses) manufacturer AF algorithms, there is always the possibility that a DSLR body might not support a (likely older) third party lens. Usually a lens can be made compatible by the manufacturer via a firmware update, but this cannot be guaranteed. There is also the risk of a problem that results in the lens and body manufacturers directing blame at each other. That Tamron USA has your back for 6 years (the warranty period) is impressive.
The evaluation lens used in this review was a retail-acquired production model.
Before making some direct comparisons between the Tamron 35mm f/1.8 Di VC USD Lens and similar lenses, I want to point out that no other non-macro prime lens offers the maximum magnification / close-up capability that this lens offers. The other feature to keep in mind is VC – only the first-compared lens below has this feature. That said, I won't keep repeating these advantages.
The other image stabilized lens that compares well to the Tamron 35 VC is the Canon EF 35mm f/2 IS USM Lens. When compared at f/2, the Tamron shows itself to be the slightly sharper lens and it continues to hold this edge at f/2.8. At f/4, I like the Canon results slightly better and at f/5.6, it doesn't matter which lens you choose in regards to image sharpness. The Canon gives up 1/3 stop of max aperture, but it is smaller, lighter and it (alone) shares the IS feature. The Tamron has slightly more flare, has less vignetting, has 9 aperture blades vs. the Canon's 8 and has a larger, easier to use focus ring. Expect the Canon to provide better AF accuracy. At review time, these lenses share the same price tag (without rebates considered).
On the Nikon side of things, the Nikon 35mm f/1.8G AF-S Lens is the standout comparison lens due to its matching focal length and max aperture. In this comparison, I prefer the Tamron's sharpness performance (keeping in mind that different camera bodies are compared here). The Nikon is smaller and lighter. I expect the Nikon to focus accurately with better consistency and it is priced lower (without rebates factored in).
Another lens I see competing strongly against the Tamron 35mm f/1.8 VC is Sigma's latest prime lens entry into this focal length, the Sigma 35mm f/1.4 DG HSM Art Lens. As I mentioned before, the Sigma has a 2/3 stop max aperture advantage, but it is the most-similar prime lens competitor in the current Sigma lineup. When compared at f/2, the Tamron has the edge in corner sharpness, but the Sigma is slightly sharper in the center of the frame. At f/2.8, the Tamron catches up to the Sigma in the center of the frame, but retains the better corner performance deeper into the aperture range. Surely a decision factor for some is that the Sigma, at review time, is priced 50% higher than the Tamron.
What about the closest zoom lens alternative? That would arguably be the Sigma 24-35mm f/2 Art Lens. Though the Sigma zoom gives up 1/3 stop of max aperture, it offers a significant versatility advantage in its zoom range. Balancing the Sigma's zoom versatility is the Tamron's VC advantage.
From an image sharpness perspective, these two lenses are competing strongly in the f/2 comparison. The Tamron has a modest lead in center of the frame performance and the Sigma has a very slight edge in the corner. At f/2.8, it becomes hard to tell a difference in sharpness.
The Tamron has slightly more lateral CA and slightly less vignetting at f/2. The Sigma trades the Tamron's slight barrel distortion for slight pincushion distortion (see the difference here). The modestly larger Sigma is nearly twice as heavy and will lighten your wallet by 50% more. Also larger are the Sigma's filter threads, measuring 82mm vs. 67mm.
There are many more lenses that can be compared to this one, with many covering the 35mm focal length. Use the site's tools to make comparisons with those you are interested in (or already have). If your budget is solid, consider the Canon EF 35mm f/1.4L II USM Lens as it is the best-available 35mm lens as of review time.
Like its 45mm sibling, the Tamron 35mm f/1.8 Di VC USD Lens brings us a lot of value for the cost. While I suggest that this lens be autofocus tested before being relied upon for critical use, the capabilities of an f/1.8 aperture combined with a well-performing vibration compensation system and a general-purpose-suited focal length are great. This attractively-designed lens delivers also-attractive image sharpness and competes very strongly against the other 35mm lens models available at review time which will make this affordable lens especially appealing to a wide range of photographers.
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