10 out of 10 points and recommendedIt's a great lens.Large and heavy to carry around, but that gives stability for handheld shooting.
Answering RawDealreviewed February 1st, 2009 (purchased for $1,600)
The essential thing to keep in mind is IMAGE SIZE.
This is determined by ONLY two things, focal length and lens-to-subject distance.
Say you mount the 70-200 lens on a D300 held for a vertical picture, set focal length at 100mm and move to a distance, D1, from your standing son such that his vertical image just fills the 23.6mm longer-dimension of the D300 sensor.
Now, without you or your son moving position or changing the lens setting, change the camera back from D300 to D700. Your son's image remains unchanged at 23.6mm, but on the D700 sensor you have more field of view above, below and around your son's image.
On the D300 your son's image would be recorded by 4288 pixels. On the D700 ,with its 36.0mm sensor dimension, your son's image would be recorded by 4256x(23.6/36.0) = 2790 pixels Actually the D700 spec sheet shows 2784 in its DX mode.
A similar proportion applies to the other dimension of the sensors. This is why. the D700 DX mode shows 5.1MP.
What to do? Zoom the lens beyond 100mm and/ or move closer until you fill the D700 sensor with your son's image. This larger image will embrace the full 4256 pixels on the D700 sensor.
Of course, the gym may restrict your lens-to-subject distance so that you cannot fill the D700 frame even at 200mm. So live with that, and don't forget that the larger individual pixel size on the D700 means lower noise, hence the opportunity to shoot at higher ISO and thus faster shutter speeds. That alone might give you sharper pics of your fast-moving son.
Stop worrying about numbers and go take pictures.