Sigma 28-70 Power Zoom
Launched 1992

One of the more unusual labour-saving devices the technology-obsessed SLR market of the late 80s and 90s brought us was the “power zoom” – supported by a limited number of cameras as a basic function, it also allowed for controlled zooming thanks to some work on the user interface by Sigma.

The original press release for this September 1992 release (counted as a 1993 lens due to availability) follows:

“Sigma Zoom 28-70mm ƒ3.5-4 UC IA Zoom has high optical performance and Intelligent Auto zoom with ultra-compact lens barrel. Sigma Intelligent Auto zoom is most sophisticated power zoom lens. Generally power zoom lens is much difficult to control the zooming and almost impossible to make exact zooming stop at the desired image size. However, Sigma Intelligent Auto Zoom is easy to control zooming like manual zoom lens and has a full make of automatic zoom function, such as image fixing wide view finder multi exposure during zooming. (Editor’s note: I used to copy type PR in the 80s and 90s; I had forgotten just how much work was required to make sense of some press releases!).

Sigma Intelligent Zoom can change the zooming speed by travelling chestance (!? – Ed.) as well as moving speed of the operation ring of the lens barrel. Also, Sigma Intelligent Zoom can make smooth and natural change of the zooming speed from start to highest speed and highest speed to stop by incorporating fuzzy logic control of the computer in the lens barrel (Fuzzy Logic was a huge buzzword around this time, and it was applied to everything from car automatic gearboxes, to washing machines to, well, lenses – Ed.)

Focal Length 28-70mm
Maximum Aperture ƒ3.5-4.5
Minimum Aperture ƒ22-27
Lens Construction 11 elements in 8 groups
Field of View 75-34° (Diagonal)

65.5-28.8° (Horizontal)

46.4-19.5° (Vertical)

Minimum Focus Distance 0.5m
Number of blades 6
Maximum Magnification 1:6.5
Zooming System Auto Zoom

Manual Zoom by rotation

Filter Size 52mm
Diameter 79mm (max.)
Length 86.5mm
Weight 350g
SRP at launch: TBA
Available Mounts: Minolta 3xi, 5xi, 7xi, 9xi