Hi LAnce,
Been meaning to write you for ages. Been following your desire to move laterally to Nikon for a while now and "wjilting" would be an apt description
The Sigma 100-300 f4 is, as most everyone described here, is a superb lens. It's AF speed with the D700 is extremely good, bested slightly by some Nikon Silient Wave lenses in this general range...but the combination of focal length range combined with performnce throughtout its range, is hard to beat. If one pixel peeps (at 100%) and is critical, it's only slight weekness is wide open at f4....but a bump in contrast and a bit of extra shapening at 300/f4, goes a long way of equalizing things. It's monor for all intent and puposes. The lens takes Sigm's 1.4x quite well and if used at 300mm, best results are achieved if stopped down a little. I've tested (and used) more than 7 samples since this lens was introduced years ago.
In contrast, the much larger and heavier Sigma 120-300 f2.8 (which I've also extensively used) is generally in the same ballpark as its little brother but has the edge at 120mm wide open and can even tolerate using Sigma's 1.4x wide open if necessary in critical situations (where the 100-300 f4 and 1.4x, does require some stopping down. Keep in mind, I don't generally like teleconverters for most aplications, so I am critical when describing performance.
Here is where Sigma's HSM deviates from Nikon's Silent Wave in terms of AF....namely that the AF "Stepping" when using "C" (continuous) AF is in incrementally larger steps (especially noticable on the 120-300 f2.8 moreso than the 100-300 f4) and when shooting moving subjects....the Af (due to this larger stepping) can sometimes not keep up as precisely as Nikon's best...and the differences in these types of situations can be readily detected and seen in resulting images.
There are still some new 100-300 f4 SIgma's around, although hard to come by. I just recently picked up one to replace an older one I had, which was given to another photographer. The much bigger and heavier Sigma 120-300 f12.8 of course is readily around...with a friend of unintentionally ending up with two new ones (will sell one at a great price).
My gut feeling is Sigma may not be updating this lens due to a number of reasons. They may feel their upcoming new 70-200 f2.8 is sufficiently imporved, so that with their 1.4x, it is essentially a 100-300 f4 and they now have other longer range OS zooms that also fill these focal length ranges (abeit slower). The Nikon 70-200 f2.8 VR with f1.4x almost fills this gap (a 100-300 f4) and it's one of those rare time that I feel a teleconverter does justice to a zoom lens.....but with its focal length "breathing"...at close to short mid-distances....it falls somewhat short of a true 300mm...so the Sigma 100-300 f4 still has that edge.
Lastly I have an aquintence that also recently (last couple of months) purchased a brand new Sigma 100-300 f4 (for Nikon) but has moved onto Canon...so I'm not sure what he's eventually going to do with his lens.
Lastly, if you pick up the Sigma...don't attempt to glue it to your K-7
Dave
