The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 70-300mm F4-5.6 DG and the Pentax 55-300mm F4.0-5.8 ED 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 70-300mm F4-5.6 DG is the longer of the two lenses at 122mm. The Pentax 55-300mm F4.0-5.8 ED with a length of 112mm, is 10mm shorter. Besides being longer, the Sigma 70-300mm F4-5.6 DG also has a larger diameter of 77mm compared to the Pentax 55-300mm F4.0-5.8 ED'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. Pentax 55-300mm F4.0-5.8 ED weighs 440g, 19% (110g) lighter than the Sigma 70-300mm F4-5.6 DG's weight of 550g.
Filter Threads
Both the Sigma 70-300mm F4-5.6 DG and the Pentax 55-300mm F4.0-5.8 ED have the same Filter thread size of 58mm.
Below are links to the 58mm filters that we recommend you to consider for these lenses:
Lens Mounts
Both the Sigma 70-300mm F4-5.6 DG and the Pentax 55-300mm F4.0-5.8 ED has the same Pentax KAF lens mount. Some of the latest released cameras that are compatible with the Pentax KAF lenses are Pentax K-3 III Monochrome, Pentax KF and Pentax K-3 III.
Sigma 70-300mm F4-5.6 DG is also available in Canon EF , Nikon F (FX), Pentax KAF, Sony Alpha, Sigma SA, Canon EF, Nikon F (FX), Sony Alpha and Sigma SA mounts.
Focal Range
Sigma 70-300mm F4-5.6 DG has a focal range of 70-300mm and
4.3X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
105 - 450mm.
On the other hand, the Pentax 55-300mm F4.0-5.8 ED has a focal range of 55-300mm and 5.5X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 82.5-450mm when used on a APS-C / DX format camera.