"It has a complicated 16-elements-in-9-groups design, a bit more complex compared to its predecessor. "The older lens has 15 elements in 8 groups:
Compared to the newer lens:
The diagrams seem to show the lenses zoomed to different focal lengths but you can see that the overall arrangement of lenses is the same except the new version has an extra meniscus lens behind the front group.
"you could meter with this more accurately and you don’t have to worry about adjusting the exposure depending on which focal-length the lens is set."Unlike other zooms I think the older 8.5-250cm f/4-4.5 is only variable aperture when set wide open. Once you stop down to f/4.5 and smaller it becomes a constant aperture lens. This was fixed with the newer 85-250/4 version, the extra lens focuses the light bundle more tightly so that mechanical vignetting is reduced, allowing for a constant f/4 aperture through the entire zoom range.
"It won’t focus close since the closest-distance is a paltry 13ft, I guess this is the limitation of the design."The 85-250 was supplied with a closeup lens. With the closeup lens attached the distance scale is reduced to 13ft - 7.5ft (4 - 2.2m). There is a secondary distance scale for the closeup lens, engraved in orange above the standard distance scale. The first zoom with a macro mode!
The 20-60cm f/9.5-10.5 is also closely related to this lens. The front part is more or less identical optically and mechanically to the 8.5-25cm f/4-4.5, except the rear doublet is absent. This increases the focal length by 2.4x, with a corresponding loss in aperture.
