How come my A700/70-200G SSM is so sluggish?

[Lone Wolf]

I could only go to the sprint in the evening so I ended up shooting mostly at night.

http://www.sgshoot.com/forums/showthread.php?p=21292#post21292

I read sometime back in this forum that it is best to turn off DRO for night shots but I forgot all about that and ended up with quite noisy pictures.

However, what puzzles me is that that night the A700 seem sluggish at focusing and tracking. Continuous burst was very slow. Normally it locks focus without me even realising it, tracks all the time I keep the subject in the viewfinder and rattles off shots faster than I can count them.
I thought it might be because of the distance and the subject is out of range of the focus assist. So I attached my flash and it improve slightly but still not as fast as usual. I am wondering if it could be because of the fluctuating light levels when I pan between pools of light or is there something wrong with my cam or lens? Could any expert here assist, pls. TIA.

[Lone Wolf]

Thanks.
With help from others and a little testing, I found a few probable causes, especially
1) Shooting at low shutter speeds slow down the continuous burst rate
2) It is beyond focus-assist lamp's range so AF slowed
It was my first time using continuous AF at such slow shutter speeds. I should have gone MF, using hyperfocal or pre-focusing. A lesson learned and glad cam and lens are ok.

[zenten04]

For a big lens like the 70-200mmm F2.8 or something within this range the compound lens elements can be quite hefty (heavy). This in turn puts some strain on the motor of the driving unit ...........

[Stanley]

For a big lens like the 70-200mmm F2.8 or something within this range the compound lens elements can be quite hefty (heavy). This in turn puts some strain on the motor of the driving unit ...........

You are right toooo! Good answer.

[Lone Wolf]

For a big lens like the 70-200mmm F2.8 or something within this range the compound lens elements can be quite hefty (heavy). This in turn puts some strain on the motor of the driving unit ...........

You are right toooo! Good answer. Actually, that is true only when comparing different lenses. When compared with other lenses, we should still bear in mind that this lens is one of those with the Supersonic Wave Motor i.e. built for "faster automatic focusing with high torque at low speed, quick start/stop response, and quiet, smooth operation". Even with its 19 elements in 16 groups, it is still one of the fastest Sony lenses and I am extremely satisfied with its AF speed and accuracy, even with my 5D but especially when coupled with the A700 (or Dynax 5) under normal conditions.
However, in this case when I had problems, I was out to test the lens and my limits in my quest to learn to get acceptable results under various conditions. It's the same motor driving the same elements in the same lens so its construction is not the problem and I feel a lot of it was due to conditions, settings and technique. The conditions was rather extreme with cars racing in very low light. Afaik, 2 friends and I were the only ones who attempted to shoot at that time. The reason I initiated this discussion is that I am not satisfied with my own results. Hopefully, I will learn enough to be able to do better with a faster lens;) at the next round.