Full-frame wide-angle lenses aren’t quite as appealing on DX format bodies thanks to the crop factor of the smaller sensor, but they can still be useful. On the Nikon D7100, of course, the 24mm lenses that occupy the number one and number two positions have the equivalent field of view to 35mm lenses (which are only moderately wide).
Be that as it may, if you have a full-frame body as well, the lenses become very versatile indeed. The Carl Zeiss Distagon T* 25mm f/2 is the best performing wide-angle lens on the D7100, with a DxOmark score of 27 points.
|Carl Zeiss Distagon T 25mm f/2 ZF.2 Nikon||1700||27||15|
|Nikon AF-S Nikkor 24mm f/1.4G ED||2200||24||13|
|Sigma 20mm F1.8 EX DG ASP RF Nikon||629||22||16|
|Samyang 14mm f/2.8 IF ED UMC Aspherical Nikon||409||21||17|
|Carl Zeiss Distagon T 21mm f/2.8 ZF2 Nikon||1732||19||10|
|Nikon AF Nikkor 20mm f/2.8D||570||19||12|
|Carl Zeiss Distagon T* 2.8/15 ZF.2 Nikon||2950||19||12|
|Carl Zeiss Distagon T 25mm f/2.8 ZF2 Nikon||1005||18||12|
|Carl Zeiss Distagon T 18mm f/3.5 ZF2 Nikon||1395||17||11|
|Sigma 14mm F2.8 EX Aspherical HSM Nikon||749||13||8|
The widely respected Nikkor 24mm f/1.4 is placed second at 24 points due in part to slightly lower levels of sharpness and some wayward CA (at least when compared with the Zeiss).
In third place is the Sigma 20mm f/1.8 EX DG Aspherical RF, another full-frame model and with a slightly wider field of view, approximating a 30mm on a full-frame camera. It has slightly higher sharpness levels than even the Zeiss but it has less homogeneity in the field (sharpness in the corner is pretty low, higher vignetting, distortion and CA).
At $629 it’s already modestly priced, given the brighter than average f/1.8 maximum aperture for this focal length. But, if brand loyalty is important, Nikon has a AF Nikkor 20mm f/2.8D model from the film era that performs well, with a DxOmark score of 19 points and a 12P-Mpix rating for sharpness.