The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Carl Zeiss Distagon T2,8/21 and the Tamron 17-50mm f2.8 XR II VC LD 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 Distagon T2,8/21 is the longer of the two lenses at 109mm. The Tamron 17-50mm f2.8 XR II VC LD with a length of 95mm, is 14mm shorter. Besides being longer, the Carl Zeiss Distagon T2,8/21 also has a larger diameter of 87mm compared to the Tamron 17-50mm f2.8 XR II VC LD's 80mm 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. Tamron 17-50mm f2.8 XR II VC LD weighs 570g, 5% (30g) lighter than the Carl Zeiss Distagon T2,8/21's weight of 600g.
Filter Threads
The Carl Zeiss Distagon T2,8/21 has a filter size of 82mm whereas the Tamron 17-50mm f2.8 XR II VC LD has a 72mm 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 Carl Zeiss Distagon T2,8/21:
And these are the 72mm filters that we recommend for the Tamron 17-50mm f2.8 XR II VC LD:
Lens Mounts
Both the Carl Zeiss Distagon T2,8/21 and the Tamron 17-50mm f2.8 XR II VC LD 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 Distagon T2,8/21 is also available in Pentax KAF and Nikon F (FX) mounts.
Tamron 17-50mm f2.8 XR II VC LD is also available in Nikon F (DX) mount.
Focal Range
Carl Zeiss Distagon T2,8/21 is a prime lens with fixed focal lenght of 21mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of
33.6mm.
On the other hand, the Tamron 17-50mm f2.8 XR II VC LD has a focal range of 17-50mm and 2.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27.2-80mm when used on a APS-C / DX format camera.