Sigma has recently unveiled the new Sigma 20mm F2 DG DN C I-series lens for Sony E and Leica L mounts. Sigma's I-series are all metal built fast prime lenses, offering good image quality in a compact package and becoming more popular among E-mount and L-mount shooters. For the E-mount, the Sony 20mm F1.8G has been the most popular lens in the 20mm focal range all for god reasons. Sony lens is selling for $899 whereas the new Sugma has a more attaractive suggested price of $699.
The Sigma 20mm is slightly slower at F2 vs the Sony's F1.8 but at the same time tthe Sigma is considerably smaller as the comparison image below shows. At 72mm, Sigma is 13mm shorter than the Sony and its diameter is 4mm less than the Sony's 74mm. Despite the size difference, thanks to the alll metal body of the Sigma, the weight difference is miniscule at only 3g between lenses.
Sigma 20mm F2 DG DN C vs Sony 20mm F1.8G E-Mount Lens Comparison
Both lenses has 9 Diaphragm blades however Sony with its slightly wider F1.8 aperture has the potential to have stronger bokeh effect compared to the Sigma. Sony also has a shorter minimum focusing distance of 0.19m and a higher max magnification ratio of 0.22x compared to Sigma's 0.15x max magnification. We didn't expect a close-up performance from an ultra wideangle lens but 0.15x is mediocre at best.
Sony 20mm F1.8G De-clickable Aperture Ring
Both lenses are weather sealed, has manual aperture rings and have AF/MF switches. The aperture lens on the Sony is de-clickable for smooth, silent aperture switching which is an advantage over the Sigma for Video shooting. Sigma also lacks the Focus hold button that is found on the Sony 20mm F1.8.
Sony 20mm F1.8G Focus Hold Button
Another advantage of the Sony 20mm F1.8 when used on Sony Alpha A7 IV is that the Breathing compensation found on the Sony camera works with the 20mm F1.8G bit won't work with the Sigma 20mm F2.0 which may be an advantage for video shooters. Check the Lens Breathing Compensation Compatible Sony Lenses here.
Apart from the image quality (we don't have the Sigma lens in our hands to do a reallife comparison yet), the Sony with its wider aperture and more features such as de-clickable aperture ring and focus hold button seems to be the more attractive lens for us. On the other hand, if price and size is more important for you, Sigma stands as a very good alternative to the Sony 20mm F1.8.
Check the specs comparison of Sigma 20mm F2 DG DN C vs Sony 20mm F1.8G:
| FEATURE and SPECS COMPARISON | |  |  |
| Model | Sigma 20mm F2 DG DN C | Sony FE 20mm F1.8 G |
| Lens Type | Prime | Prime |
| Lens Mount | Sony E | Sony E |
| Focal Length | 20mm | 20mm |
| Max Format | 35mm FF | 35mm FF |
| Number of Diaphragm Blades | 9 | 9 |
| Optical Elements | 13 | 14 |
| Optical Groups | 11 | 12 |
| Minimum Focus Distance | 0.22m | 0.19m |
| Max Magnification | 0.15x | 0.22x |
| Weight | 370g | 373g |
| Length | 72mm | 85mm |
| Diameter | 70mm | 74mm |
| Filter Thread | 62mm | 67mm |
| Weather Sealing | | |
| Aperture Ring | | |
| Price | Amazon, B&H Photo | Amazon, B&H Photo |