The Sigma 70-210mm f/2.8 APO is about average for its focal length and aperture in terms of size and weight. The Sigma 70-210mm f/2.8 APO as the name suggests incorporates specialized glass to reduce chromatic aberrations. The lens is constructed of 17elements in 13 groups with 3 SLD glass elements. Two versions of the lens were made around the same time, apparently one with a 77mm filter diameter that supposedly vignetted some and one with an 82mm filter diameter made later; the version I have appears to be the 82mm filter diameter lens. I am not sure which years which version was made and the only dates of manufacture I have is 1992-1995 range, but that might be only the 77mm version or it might be both. The total length of the lens is 192mm with a weight of 1300g (2.9lbs). The lens has a close focusing distance of 6ft/1.8m with a maximum reproduction size of 1:7.2 at 210mm.
Size comparison with hood on to Zuiko 50mm f/1.8
The lens is an internal focus/zoom design so the lens never varies in length nor the front element rotate. The lens is a two touch design with a separate zoom and focus rings. The zoom elements are quite heavy and shooting at more then about 45 degrees up or down will cause zoom creep (towards the long end +45 and the short end -45) A light touch on the zoom ring will prevent this. The lens has a very sturdy tripod collar that rotates freely when released and locks down solidly. The design is very easy to remove, you loosen the collar lock nut and then pull it to release the collar and reattaching is just as easy. The tripod collar is just about the perfect size to provide a good rest to the heel of your hand when shooting with the lens.
The aperture range on the lens is from f/2.8 to f/22 in half stop steps. The aperture ring is snappy, but not to hard to rotate. The lens zooms easily and the focus takes a quarter turn to go from infinity to closest focus and also rotates easily. The lens hood is a bayonet type hood (plastic, but quite sturdy) that attaches outside of the filter ring on the bayonet lugs. The attachment is very firm and not likely to dislodge. The hood can be attached backward for storage.
Comparable lenses in OM mount are the Tamron Adaptall-2 80-200mm f/2.8 and the Tokina 80-200mm f/2.8.
The lens is pretty sharp wide open as the example pictures below show.
70mm f/2.8 1/125s 210mm f/2.8 1/250s
210mm f/2.8 1/250s