The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Tamron 18-400mm F3.5-6.3 VC and the Sigma 18-200mm F3.5-6.3 DC OS HSM C 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. Tamron 18-400mm F3.5-6.3 VC is the longer of the two lenses at 124mm. The Sigma 18-200mm F3.5-6.3 DC OS HSM C with a length of 86mm, is 38mm shorter. Besides being longer, the Tamron 18-400mm F3.5-6.3 VC also has a larger diameter of 79mm compared to the Sigma 18-200mm F3.5-6.3 DC OS HSM C's 71mm 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. Sigma 18-200mm F3.5-6.3 DC OS HSM C weighs 430g, 39% (280g) lighter than the Tamron 18-400mm F3.5-6.3 VC's weight of 710g.
Filter Threads
The Tamron 18-400mm F3.5-6.3 VC has a filter size of 72mm whereas the Sigma 18-200mm F3.5-6.3 DC OS HSM C has a 62mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 72mm filters that we recommend you to consider for the Tamron 18-400mm F3.5-6.3 VC:
And these are the 62mm filters that we recommend for the Sigma 18-200mm F3.5-6.3 DC OS HSM C:
Lens Mounts
Both the Tamron 18-400mm F3.5-6.3 VC and the Sigma 18-200mm F3.5-6.3 DC OS HSM C has the same Nikon F (DX) lens mount. Some of the latest released cameras that are compatible with the Nikon F (DX) lenses are Nikon D3500, Nikon D7500 and Nikon D5600.
Tamron 18-400mm F3.5-6.3 VC is also available in Canon EF-S mount.
Sigma 18-200mm F3.5-6.3 DC OS HSM C is also available in Canon EF , Pentax KAF3, Sony Alpha and Sigma SA mounts.
Focal Range
Tamron 18-400mm F3.5-6.3 VC has a focal range of 18-400mm and
22.2X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
27-600mm when used on a APS-C / DX format camera.
On the other hand, the Sigma 18-200mm F3.5-6.3 DC OS HSM C has a focal range of 18-200mm and 11.1X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-300mm when used on a APS-C / DX format camera.