The Sigma 20mm f 1.8 lens has broken 2 records. The first one is being the fastest 20mm lens in the market. And the second one is being the worst Sigma prime lens in terms of optical performance.
Sigma made this lens for Sigma
Surprising? Yes. Expected? Yes.
Sigma is being very aggressive with the f/1.8 aperture at the cost of image quality. Also, there is another additional cost of inflated lens dimension.
The filter size of this lens is 82mm which is HUGE! This is even bigger when compared to constant aperture zoom lens.
In terms of optical performance, sharpness is very soft at f/1.8 both on the center and borders. Also, it suffers from high vignetting on this aperture.
Note that I tested this lens on a cropped sensor DSLR and got the above results. Imagine how it would perform when tested on a full frame DSLR!
Chromatic aberration control is the only thing that is AVERAGE on this lens.
Although this lens has a record breaking f/1.8 aperture and most users would want to grab it because it looks promising, I would recommend you to avoid this lens.
If you are still not convinced, read on the full Sigma 20mm f 1.8 below to see the complete proof and findings.
Specs • Performance • Sample Image • Conclusion • Where to Buy
Sigma 20mm f 1.8 Specs
Back to: Menu • Introduction
Official Name:
Sigma 20mm f/1.8 EX DG ASP RF
Focal Length Markings:
20mm
Features:
EX – Excellent – Sigma’s designation for their high end lenses.
DG – Compatible with both full frame and cropped sensor DSLR camera.
ASP – Aspherical – Sigma lenses with this term is usually smaller in dimension compared to its peers.
RF – Rear Focus – Rear element is moved for quieter and faster autofocusing operation.
Full Technical Specs (from Sigma’s website):
| Technical Specifications | |
| Groups / Elements | 11 / 13 |
| Angle of View | 94.5 |
| Number of Blade Diaphragm | 9 |
| Minimum Aperture | f/22 |
| Minimum Focusing Distance | 7.9in. (0.2m) |
| Filter Thread | 82mm |
| Weight | 18.3oz. (520g) |
| Dimension (Diameter x Length) | 3.5 x 3.4in. (88.5 x 87mm) |
| Macro Magnification Ratio | 1:4 |
| Available for | Sigma, Nikon, Canon, Sony, Pentax |
Optical Performance
Back to: Menu • Introduction
Sigma 20mm f 1.8 Sharpness
Center sharpness is a bit disappointing at f/1.8. At other apertures it is just OK, but not great.
Borders at f/1.8 is VERY DISAPPOINTING. It is very soft and lack of clarity. Stopping down to f/2.8 will greatly improve this.
The optimal aperture on this lens is at f/4. Although I say this is the optimal, the quality is disappointing since any kit zoom lens would be able to beat the sharpness of this lens easily, even at f/4!
See the full sharpness test table below.
Sharpness Scale (from Best to Worst):
(5) Excellent
(4) Great
(3) Good
(2) Fair
(1) Poor
Sigma 20mm f/1.8 EX DG ASP RF Center Sharpness
| Focal Length / Aperture | f/1.8 | f/2.8 | f/4 | f/5.6 | f/8 |
| 20mm | Good | Great | Great | Great | Excellent |
Sigma 20mm f/1.8 EX DG ASP RF Border Sharpness
| Focal Length / Aperture | f/1.8 | f/2.8 | f/4 | f/5.6 | f/8 |
| 20mm | Poor | Good | Great | Great | Great |
Distortion
Being a wide angle lens, distortion is visible on this lens. It is not to the extreme degree, but other lens has performed much better.
See the distortion test result for this Sigma 20mm f 1.8 lens below.
Sigma 20mm f 1.8 Distortion
Vignetting
Again, the f/1.8 is a major problem in the vignetting test. Tested on a cropped sensor DSLR, vignetting is a VERY VISIBLE.
You’ll need to stop down to f/2.8 to reduce it greatly, f/4 to completely eliminate it.
See the vignetting test results below for the test proof.
Sigma 20mm f 1.8 Vignetting
Chromatic Aberration
Chromatic aberration is quite decent. It is not as bad as the other optical defects, but not great either.
You’ll need to stop down all the way to f/8 to eliminate it completely.
Chromatic Aberration Scale (from Best to Worst):
(5) Negligible
(4) Very Low
(3) Low
(2) High
(1) Very High
Sigma 20mm f/1.8 EX DG ASP RF Chromatic Aberration
| Focal Length / Aperture | f/1.8 | f/2.8 | f/4 | f/5.6 | f/8 |
| 20mm | Low | Low | Low | Low | Very Low |
Build Quality
Back to: Menu • Introduction
Materials
The build quality is quite decent, typical of Sigma EX lens (crinkle finish).
Focusing
There is a feature on this lens called Dual Focus (DF) mechanism that allows you to detach the focus ring from the gear by pulling/pushing it.
Autofocus performance is quite decent and accurate on this lens and the focus ring is quite smooth.
Note that this is not an HSM lens which means it will not autofocus when used with entry level Nikon DSLR such as Nikon D40, D40x, D60, D5000, D5100, D3000 and D3100.
Image Stabilization
There is no Optical Stabilization built into the lens.
Compatibility
Being a DG lens, this lens is compatible with both full frame and cropped sensor DSLR camera.
Sample Image
Back to: Menu • Introduction
The following are some images taken with this lens. Click any of them to enlarge the image.
Get the best price online from Amazon: Sigma
Conclusion
Back to: Menu • Introduction
Here are my summary on this rather disappointing lens review.
If you have read my test above, then you’ll note that f/1.8 is the biggest problem on this lens.
At f/1.8, it is very soft both on the center and borders. Heavy vignetting also appear at f/1.8.
Distortion is also visible on this lens although easily correctable. Chromatic aberration control is just OK, but not great.
In terms of build quality, this lens is quite good, typical of any Sigma EX lenses. However, do take precaution because you need to protect the big front element from bumping to any objects.
Overall, I would not recommend this lens. Sure it might break the record as being the fastest 20mm lens out there, but it does so at the cost of poor performance.
There are also better alternatives out there. Bottom line: avoid.
Drawbacks
- Very soft on the center and on the borders at f/1.8
- Heavy vignetting at f/1.8
- Distortion is visible
Positives
- Good build
Good For
- Hmm… very hard to come up with one.
Not So Good For
- Photographers expecting to get sharp pictures from this lens
What Others Are Saying…
by “Matthew Howe”
A 20mm f1.8 prime for $400.00? What was I thinking? At f1.8 the lens is unacceptably soft. Better at 2.8, but still not great. It’s not until f4 that the Sigma matched the sharpness of my Nikon…
Click here to see the full review
by “John Kahrs”
Images from this lens plagued with bad detail, poor contrast, and the out-of-focus areas are harsh and filled with unpleasant artifacts. I never think twice about bokeh, whether its bad or good, but this is bad…
Click here to see the full review
Where to Buy
Support this site, buy the Sigma 20mm f 1.8 lens from Amazon (best price online):
If the mount you’re looking for is not available on Amazon, check out B&H Photo (Sigma, Nikon, Canon, Sony, Pentax) or Adorama (Sigma, Nikon, Canon, Sony, Pentax)
Stay away from this lens, below are some more options that you can look at.
Hope you’ve enjoyed this revealing Sigma 20mm f 1.8 lens review and I will catch you in the next one!
The Sigma 20mm f 1.8 lens has broken 2 records. The first one is being the fastest 20mm lens in the market. And the second one is being the wo…
The Sigma 20mm f 1.8 lens has broken 2 records. The first one is being the fastest 20mm lens in the market. And the second one is being the wo…
| Lens Score | |
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| Optical Quality | |
| Build Quality | |
| Value for Money | |
| Overall | |
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