Sigma AF 20mm f/1.8 EX DG ASPHERICAL RF

(7 customer reviews)

This photographic lens is a good alternative for photographers who want to capture wide angle shots. It has autofocus capabilities and can also be used manually. The lens is made up of several glass elements, including aspherical elements, which helps to reduce distortion and improve image quality. It also has a lens coating to reduce glare and improve contrast. The lens has a wide aperture of f/1.8, which allows for good low-light performance and shallow depth of field. The build quality of the lens is good and it is durable. The lens has a good resolution and can produce sharp images. The manufacturing time of the lens is not mentioned.


– The wide aperture of f/1.8 allows for great low-light performance and depth of field control.
– The focal length of 20mm is perfect for capturing breathtaking landscape shots.
– The aspherical element produces sharp and distortion-free images.
– The build quality is solid and durable.


– The lens is quite heavy and bulky, which can be cumbersome for extended shooting sessions.
– The autofocus can be slow and noisy at times.
– The price point may be a deterrent for budget-conscious photographers.


Overall, the Sigma AF 20mm f/1.8 EX DG ASPHERICAL RF camera lens is a great investment for those who are serious about capturing stunning landscape and astrophotography shots. While it may have its drawbacks, the image quality and versatility of this lens make it a worthwhile addition to any photographer’s equipment. If you are willing to spend the money and don’t mind a bit of weight, then this lens is definitely worth considering.

Optical design

Has 9 aperture blades, with this amount of aperture blades you will be satisfied with the result. Wide open, subjects located outside the depth of field are shown very blurred.

Physical characteristics

With a lens filter diameter of 82 mm lens filters in this range can be expensive, purchase lens – and filter – only if you plan to keep them for long time, make a try with used ones. Weights 520 grams so plan ahead, carry only if really necessary. 87 mm long, requires consideration if you want to carry in the camera bag.

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7 reviews for Sigma AF 20mm f/1.8 EX DG ASPHERICAL RF


    4.0 user rated as 4.57/5

  2. rated as 4.54/5

  3. Dec 18, 2017

    Quality low-light, wide-angle, full frame lens. If you want a fast aperture (f/1.8), wide-angle (20mm), full frame sensor capable prime lens you have virtually no other options under $1,000.

    Quality build–a bit heavy with a fully mechanical auto focus/manual focus (de)coupler. Feels solid holding and focusing. Fast auto focus.

    OK sharpness wide open @ f1.8. Good center sharpness @ f4.0 and up. Low distortion and CA. Extreme close focus ability with decent bokeh.

    Get to know its limitations and you can excel at photo taking with this specialty lens.

  4. Mar 07, 2011

    Surprising Sharpness Considering Its Reputation I bought this as an additional secret weapon for weddings and industrial hand held, low-light shooting. This is the latest version of this lens (there is an older version that is not “DG”).

    This lens is either loved or hated apparently due to the Sigma curse of poor quality control. I’ve been lucky with Sigma’s so far, but I’ve had friends that had to send their lenses back. To Sigma’s credit, they always seem to return a well adjusted and properly operating lens.

    This copy is pretty soft in the center at F/1.8 which is about what you’d expect. However — and to me inexplicably — just a 1/3 stop closure to F/2 clears things up immensely. I’ve shot it on my D200 and my D7000 and it works well on each, though I had to dial in correction for a bit of back focusing which is only really apparent on very shallow depth of field shots.

    Shooting it on DX (1.5x crop, the edges are soft until you start to hit F/2.8 or so and not really getting sharp until F/4 — but by F/5.6 the lens is extraordinarily sharp.

    There’s little out there at this wide an angle that is as affordable as this lens. For many shots, that gauzy softness — particularly for weddings — might be actually usable. Some carefully applied masked sharpening can work wonders to make a nice looking shot. Soft focus and noise clean up better than motion blur.

    One of the wonders is how close this thing focuses. This is one of the lens strengths/weaknesses. Some said the lens just wasn’t as sharp when wide open at close focus as it was nearer infinity. My copy seems to be the opposite of that. Wide open shots at f/1.8 a few inches from the lens appear sharper than the shots further away. Could be an anomaly and it’s not dramatic but that’s what I think I’m seeing.

    Overall, a surprisingly useful lens at F/2 where I will choose to shoot it for very low light performance. This lens, paired with the good high-iso noise of my D7000, can make some shots possible that I normally would not bother with knowing that there would be no usable quality.

    Although it seems these lenses can be a “crap shoot”, I recommend getting one if you need something very fast and fairly wide. For this price you can certainly find something you can use it for when you have no other options.

    If, like me, you have old Nikon film cameras then you will like that this lens has a real aperture ring. Since the lens is full-frame compatible it can be used as an ultra wide lens on full frame and film cameras — through frankly with it’s edge sharpness issues on DX I would think using it on film/FX would require careful framing and limit your applications at large aperture.

    My version is for Nikon AF and I presume the other versions are similar in this respect: there’s no motor in the lens. It is entirely dependent on the focus drive motor in the camera which means slightly slower focus performance and a bit more noise. Still, I don’t consider this lens excessively noisy or slow but if you’re used to a professional AF-S or USM style lens this is a step back. Not bad for a motor driven AF lens from Sigma though.

    A word on build quality: this is a Sigma EX (top-of-the-line) lens and it feels solid. Certainly it’s huge for a prime with its nearly 4″ length and 82mm filter. It has the hokey focus clutch like a Tokina which I’m not fond of, but I don’t focus this one manually anyway so who cares. Just make sure the focus ring is pushed forward towards the objective when you use it.

  5. Jun 16, 2008

    Surprisingly good for the price! Very bright lens at this focal length. Surprisingly sharp, even though the edges lose some sharpness. So, it may not be the best lens for film or full-frame digital cameras, but with the crop factor of many digital SLR’s, the edge sharpness in negligible. Still, given the price, this is an excellent lens for all formats. One thing that could be better is focusing speed. It’s kind of slow, so I recommend manual focusing, especially in low light conditions.

  6. Dec 21, 2010

    Awesome at f1.8 The lens does exactly what I’d hoped for, shooting environmental portraits where the subject is tack sharp and the wider view is out of focus but discernible. I had loved the shots I’d seen pros make with the Nikkor 24mm f1.4 at f1.4, but as an amateur can’t justify $2k+ for a specialty lens. The Sigma 20mm f1.8 does nearly the same thing on my Nikon DX body when shot at f1.8. At a few feet away the DOF is about 1′ so it’s not super picky focusing but still does a nice job of blurring backgrounds that are 6′ or further away, making your subject really pop. At an equivalent of 30mm it works nicely for portraits as the edge of frame distortion is not too high if you shoot off level and center. It’s plenty sharp at f1.8 for portraits and focuses well. It was the lens I was looking for in my budget.

  7. Apr 28, 2016

    Just what I needed. I have already taken some nice landscape pictures and plan on using it for astrophotography.

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