The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 4.5mm F2.8 EX DC HSM Fisheye and the Hartblei 40mm F4 IF TS for their suitability to various photography scenarios:
Size and Weight Comparison
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 4.5mm F2.8 EX DC HSM Fisheye weighs 470g, which means it is 1080g (69%) lighter than the Hartblei 40mm F4 IF TS which has a weight of 1550g.
Lens Mounts
The Sigma 4.5mm F2.8 EX DC HSM Fisheye has the Nikon F (DX) lens mount whereas the Hartblei 40mm F4 IF TS has the Sony Alpha lens mount. Some of the latest released cameras that are compatible with these mounts are Nikon D3500, Nikon D7500 and Nikon D5600 for the Nikon F (DX) Mount and Sony A99 II, Sony A68 and Sony A77 II for the Sony Alpha Mount.
Sigma 4.5mm F2.8 EX DC HSM Fisheye is also available in the Canon EF and Sigma SA mounts.
Hartblei 40mm F4 IF TS is also available in Canon EF , Pentax KAF and Nikon F (FX) mounts.
Focal Range
Sigma 4.5mm F2.8 EX DC HSM Fisheye is a prime lens with fixed focal lenght of 5mm which has an effective (full-frame 35mm equivalent) focal range of
7.5mm when used on a APS-C / DX format camera.
On the other hand, the Hartblei 40mm F4 IF TS is a prime lens with fixed focal lenght of 40mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 60mm.
