The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Carl Zeiss Apo Sonnar T2/135 and the Canon 85mm f1.8 USM 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. Carl Zeiss Apo Sonnar T2/135 is the longer of the two lenses at 128mm. The Canon 85mm f1.8 USM with a length of 72mm, is 56mm shorter. Besides being longer, the Carl Zeiss Apo Sonnar T2/135 also has a larger diameter of 84mm compared to the Canon 85mm f1.8 USM's 75mm 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. Canon 85mm f1.8 USM weighs 425g, 53% (495g) lighter than the Carl Zeiss Apo Sonnar T2/135's weight of 920g.
Below you can find the dimension and weight table of the Telephoto Prime Lenses in Canon EF Mount for size comparison purposes.
Telephoto Lenses in Canon EF Mount for Size Comparison
Filter Threads
The Carl Zeiss Apo Sonnar T2/135 has a filter size of 77mm whereas the Canon 85mm f1.8 USM has a 58mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 77mm filters that we recommend you to consider for the Carl Zeiss Apo Sonnar T2/135:
And these are the 58mm filters that we recommend for the Canon 85mm f1.8 USM:
Lens Mounts
Both the Carl Zeiss Apo Sonnar T2/135 and the Canon 85mm f1.8 USM has the same Canon EF lens mount. Some of the latest released cameras that are compatible with the Canon EF lenses are Canon 1D X III, Canon 6D MII and Canon 5D MIV.
Carl Zeiss Apo Sonnar T2/135 is also available in Nikon F (FX) mount.
Focal Range
Carl Zeiss Apo Sonnar T2/135 is a prime lens with fixed focal lenght of 135mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of
216mm.
On the other hand, the Canon 85mm f1.8 USM is a prime lens with fixed focal lenght of 85mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 136mm.