Early this year, I acquired a used 20mm ƒ/1.8G Nikkor lens. I only have DX bodies and the 20mm works more like a wide-normal prime than an ultra-wide, as on FX.
Why use 20mm ƒ/1.8G? on DX?
I had long wanted to have a small, fast 24mm prime for my DX bodies. While the 35mm ƒ/1.8 DX is compact enough, I don’t like it that much. The FoV (51mm FX equivalent) is too narrow for general photography and too wide for portraits. I do most of my portrait work with a 50mm ƒ/1.8G, so I need something to cover the wider end.
The 20mm is not a bad option. Its 30mm FX equivalent FoV actually matches that of some very popular smartphones, which is what I intended this lens for – having a smartphone camera equivalent with much superior image quality.
How Good is the 20mm ƒ/1.8G?
Sharpness
The lens is incredibly sharp. The 24MP DX sensor is the most demanding configuration for lenses across any system but there’s nothing that the 20mm ƒ/1.8G leaves on the table in terms of detail. The corners are not as sharp as the centre but that’s expected from a rectilinear wide-angle lens. Anyway, it easily out-resolves the wide zooms available for DX. While you can find MTF numbers etc. published by professional reviewers, I can tell you that at ƒ/8 in daylight, I need to reduce the default sharpness setting on my RAW converter for this lens. This is in the league of 85mm ƒ/1.8G performance, which itself is well known for its sharpness.
Rendering
This is my first lens with Nikon’s Nano Crystal coating and while I’ve not found any solid endorsements for the coating from pro photographers, I feel it gives a different “look” to the pictures. Its contrast and edge acuity feels a lot like that of the Zeiss T* equipped lenses, like in the Sony RX100. The biggest impact of this coating is felt with high ISO images where the extra edge definition and micro-contrast helps the noise-reduction algorithms retain the details better.
Close-Up Shooting
The 20mm ƒ/1.8G focuses down to a minimum distance of 20 cm from the sensor, which roughly works out to 7 cm from the front of the lens. That is pretty close for most situations. This is not a macro/micro lens, though, since its wide FoV means that even at this close distance, its maximum magnification is only about a quarter of a true macro lens. Having said that, this is good enough for some funny people photography and taking pictures of food, gadgets, etc.
Shortcomings
While the 20mm ƒ/1.8G is a cracker of a lens, it does have a couple of issues, both to do with its applicability. The first is its size and weight. With an 82mm diameter and 355g weight, this is one big prime – twice as big as the 35mm ƒ/1.8G DX. I would have loved for it to be about the size of a 50mm ƒ/1.8D – that noisy little lens. I wish for a DX DSLR equivalent of the Fuji X100, but there’s a bulk tax that Nikon’s DX shooters must pay for the lack of proper DX primes.
The second issue is with AF accuracy on the D7100. While the lens focuses on the right thing with the D3300’s 11-point AF system, the 53-point AF module sometimes doesn’t focus on the intended target. 3D tracking AF is too unpredictable to use. AF-S works most of the time but close focusing against a distracting background needs some care. I think it’s got more to do with the combination of a large aperture and wide focal length rather than operational defects in the equipment.
Conclusion
The 20mm ƒ/1.8G Nikkor makes for a great general purpose lens on DX bodies, but its size and weight hamper the portability a bit. Nonetheless, its combination with the current Nikon 24MP DX sensors is great for low light social photography or taking pictures of food, etc.
The nice thing is, if you pair your DX body with an FX body, this very lens would give an ultra-wide FoV on FX. There is a narrow range of focal lengths (19-25mm, I reckon) where the DX crop factor changes the perspective significantly enough to allow the same lens to be used as two different lenses in an FX-DX pairing. The 20mm falls well within that range.
