Size and Weight Comparison
The size of a lens is a crucial factor to consider when comparing two lenses. Sigma 17mm F4 DG DN C is the longer of the two lenses at 49mm. The Sigma 45mm F2.8 DG DN C with a length of 46mm, is 3mm shorter. On the other hand, there is no difference between the max diameters of these lenses, both coming at 64mm.
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 45mm F2.8 DG DN C weighs 215g, 4% (10g) lighter than the Sigma 17mm F4 DG DN C's weight of 225g.
Filter Threads
Both the Sigma 17mm F4 DG DN C and the Sigma 45mm F2.8 DG DN C have the same Filter thread size of 55mm.
Below are links to the 55mm filters that we recommend you to consider for these lenses:
Lens Mounts
Both the Sigma 17mm F4 DG DN C and the Sigma 45mm F2.8 DG DN C has the same Leica L lens mount. Some of the latest released cameras that are compatible with the Leica L lenses are Leica SL3, Panasonic S5 II and Panasonic S5 II X.
Sigma 17mm F4 DG DN C is also available in Sony E mount.
Sigma 45mm F2.8 DG DN C is also available in Sony E mount.
Focal Range
Sigma 17mm F4 DG DN C is a prime lens with fixed focal lenght of 17mm.
On the other hand, the Sigma 45mm F2.8 DG DN C is a prime lens with fixed focal lenght of 45mm.