The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 135mm F1.8 DG HSM A and the Leica APO-SL 90mm F2 ASPH 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. Sigma 135mm F1.8 DG HSM A is the longer of the two lenses at 139mm. The Leica APO-SL 90mm F2 ASPH with a length of 102mm, is 37mm shorter. Besides being longer, the Sigma 135mm F1.8 DG HSM A also has a larger diameter of 91mm compared to the Leica APO-SL 90mm F2 ASPH's 73mm diameter.
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Below you can find a scaled side-by-side image of Sigma 135mm F1.8 DG HSM A and Leica APO-SL 90mm F2 ASPH to get a better idea of how their sizes compare in real life.
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. Leica APO-SL 90mm F2 ASPH weighs 700g, 38% (430g) lighter than the Sigma 135mm F1.8 DG HSM A's weight of 1130g.
Below you can find the dimension and weight table of the Telephoto Prime Lenses in Leica L Mount for size comparison purposes.
Telephoto Lenses in Leica L Mount for Size Comparison
Filter Threads
The Sigma 135mm F1.8 DG HSM A has a filter size of 82mm whereas the Leica APO-SL 90mm F2 ASPH has a 67mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 82mm filters that we recommend you to consider for the Sigma 135mm F1.8 DG HSM A:
And these are the 67mm filters that we recommend for the Leica APO-SL 90mm F2 ASPH:
Lens Mounts
Both the Sigma 135mm F1.8 DG HSM A and the Leica APO-SL 90mm F2 ASPH 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.
Focal Range
Sigma 135mm F1.8 DG HSM A is a prime lens with fixed focal lenght of 135mm.
On the other hand, the Leica APO-SL 90mm F2 ASPH is a prime lens with fixed focal lenght of 90mm.