DPRTV posted their Sigma 28-70mm review filmed on the Pentax K-01 so the quality is quite lacking, but it is interesting to see how Jordan gets around the limitations with dubbed audio and more. Below is a summary of their review:
Very small and compact
67mm filter thread
474g
Worlds smallest 28-70mm f/2.8 full-frame lens
Tamron is basically the same dimentions with 28-75mm of range, but a little bit heavier
This lens is mostly polycarbonate with a metal lens mount
The lens is not weather sealed
Well dampened zoom and manual focus ring
No OIS
Little ghosting in the far corner, but impressive all around
Better at the wide-angle than the telephoto range
AF is very quick
Very little breathing at 70mm with a little more at 28mm
Bokeh has a lot of cats eye in the corners and even towards the center of the frame, but it is otherwise nice
Bokeh remains round as you stop down, which helps with the cats eyes
No major chromatic abbreviation, but there is some LoCA
Barrel distortion at 28mm with pincushion distortion at 70mm
Sharpness is pretty good in the center at 70mm f/2.8 but gets better by f/5.6
Corners aren’t very sharp even stopped down at 70mm
At 28mm the corners are better and the center sharpness is good at f/2.8, but gets better at f/5.6
This lens is a nice performer stopped down, but wide open it depends
The problem is the Tamron is a very good lens that is otherwise excellent outside of some distracting bokeh