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 FA 77mm 1.8 L 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 FA 77mm 1.8 L with a length of 48mm, is 74mm shorter. Besides being longer, the Sigma 70-300mm F4-5.6 DG also has a larger diameter of 77mm compared to the Pentax FA 77mm 1.8 L's 64mm 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 FA 77mm 1.8 L weighs 270g, 50% (280g) lighter than the Sigma 70-300mm F4-5.6 DG's weight of 550g.
Filter Threads
The Sigma 70-300mm F4-5.6 DG has a filter size of 58mm whereas the Pentax FA 77mm 1.8 L has a 49mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 58mm filters that we recommend you to consider for the Sigma 70-300mm F4-5.6 DG:
And these are the 49mm filters that we recommend for the Pentax FA 77mm 1.8 L:
Lens Mounts
Both the Sigma 70-300mm F4-5.6 DG and the Pentax FA 77mm 1.8 L 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 Mono, Pentax KF and Pentax K-3 III.
Sigma 70-300mm F4-5.6 DG is also available in the Canon EF , Nikon F (FX), Sony Alpha, Sigma SA, Canon EF, Nikon F (FX), Pentax KAF, 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 FA 77mm 1.8 L is a prime lens with fixed focal lenght of 77mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 115.5mm.
