The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 800mm F5.6 EX DG HSM and the Sigma 18-250mm F3.5-6.3 DC OS HSM 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 800mm F5.6 EX DG HSM is the longer of the two lenses at 521mm. The Sigma 18-250mm F3.5-6.3 DC OS HSM with a length of 101mm, is 420mm shorter. Besides being longer, the Sigma 800mm F5.6 EX DG HSM also has a larger diameter of 157mm compared to the Sigma 18-250mm F3.5-6.3 DC OS HSM's 79mm 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 18-250mm F3.5-6.3 DC OS HSM weighs 628g, 87% (4272g) lighter than the Sigma 800mm F5.6 EX DG HSM's weight of 4900g.
Filter Threads
The Sigma 800mm F5.6 EX DG HSM has a filter size of 46mm whereas the Sigma 18-250mm F3.5-6.3 DC OS HSM 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 46mm filters that we recommend you to consider for the Sigma 800mm F5.6 EX DG HSM:
And these are the 72mm filters that we recommend for the Sigma 18-250mm F3.5-6.3 DC OS HSM:
Lens Mounts
Both the Sigma 800mm F5.6 EX DG HSM and the Sigma 18-250mm F3.5-6.3 DC OS HSM has the same Sigma SA lens mount. Some of the latest released cameras that are compatible with the Sigma SA lenses are Sigma Quattro, Sigma Quattro H and Sigma SD1 Merrill.
Sigma 800mm F5.6 EX DG HSM is also available in the Canon EF and Nikon F (FX) mounts.
Sigma 18-250mm F3.5-6.3 DC OS HSM is also available in Canon EF , Nikon F (DX), Pentax KAF3, Sony Alpha, Sigma SA, Canon EF, Nikon F (DX), Pentax KAF3 and Sony Alpha mounts.
Focal Range
Sigma 800mm F5.6 EX DG HSM is a prime lens with fixed focal lenght of 800mm.
On the other hand, the Sigma 18-250mm F3.5-6.3 DC OS HSM has a focal range of 18-250mm and 13.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 27-375mm when used on a APS-C / DX format camera.
