The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 19mm F2.8 EX DN and the ZEISS Loxia 21mm F2.8 for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is a crucial factor to consider when comparing two lenses. ZEISS Loxia 21mm F2.8 is the longer of the two lenses at 72mm. The Sigma 19mm F2.8 EX DN with a length of 46mm, is 26mm shorter. Besides being longer, the ZEISS Loxia 21mm F2.8 also has a larger diameter of 62mm compared to the Sigma 19mm F2.8 EX DN's 61mm diameter.
The weight of a lens is equally significant as its external dimensions, particularly if you intend to handhold your camera and lens combination for extended periods. Sigma 19mm F2.8 EX DN weighs 140g, which means it is 254g (64%) lighter than the ZEISS Loxia 21mm F2.8 which has a weight of 394g.
Below you can find the dimension and weight table of the Wideangle Prime Lenses in Sony E Mount for size comparison purposes.
Wideangle Lenses in Sony E Mount for Size Comparison
Filter Threads
The Sigma 19mm F2.8 EX DN has a filter size of 46mm whereas the ZEISS Loxia 21mm F2.8 has a 52mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 46mm filters that we recommend you to consider for the Sigma 19mm F2.8 EX DN:
And these are the 52mm filters that we recommend for the ZEISS Loxia 21mm F2.8:
Lens Mounts
Both the Sigma 19mm F2.8 EX DN and the ZEISS Loxia 21mm F2.8 has the same Sony E lens mount. Some of the latest released cameras that are compatible with the Sony E lenses are Sony A6700, Sony FX30 and Sony ZV-E10.
Sigma 19mm F2.8 EX DN is also available in Micro Four Thirds mount.
Focal Range
Sigma 19mm F2.8 EX DN is a prime lens with fixed focal lenght of 19mm which has an effective (full-frame 35mm equivalent) focal range of
28.5mm when used on a APS-C / DX format camera.
On the other hand, the ZEISS Loxia 21mm F2.8 is a prime lens with fixed focal lenght of 21mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 31.5mm.