An-D wrote:Quote:
Plus, I haven't seen a 70-210 lens that has an f-stop that's any better than a plain-jane 70-300 (F4-5.6).
There are a number of zoom lenses in the 70-200mm range that offer f/2.8 throughout their focal range. Virtually every major camera manufacturer offers at least one zoom like this, because these types of lenses are necessary for low light sports in order to get faster AF and faster shutter speeds for less motion blur. Ditto for the 3rd party lens manufacturers. For example, the Sigma 70-200mm f/2.8 EX series lenses are very popular with shooters that need faster shutter speeds in low light.
These f/2.8 lenses are at least twice as bright as a consumer grade 70-300mm lens (f/2.8 is exactly twice as bright as f/4), with even more difference in brightness as you zoom in.
So, a 70-200mm f/2.8 would you to get shutter speeds at least twice as fast for any given lighting and ISO speed as a lens that only has f/4 available. You'd get shutter speeds 4 times as fast as a lens that only has f/5.6 available (f/2.8 is 4 times as bright as f/5.6).
A brighter lens can also help a camera's Autofocus to "see" better in low light, with faster AF and less hunting (because it's brighter and the AF sensors get more light).
Even if you used a 1.5x TC to extend the range of a 70-200mm f/2.8 out to 300mm, you'd still get shutter speeds twice as fast at 300mm compared to a zoom with a largest available aperture of f/5.6 on it's long end (since you'd lose one stop of light with a 1.5x TC which would give you f/4 at 300mm on a 70-200mm f/2.8, versus the f/5.6 you'd have with a consumer grade Zoom.
In addition to shutter speed and Autofocus issues, some photographers may appreciate the shallow Depth of Field they get shooting at a wider f/2.8 aperture.
There is a reason that these lenses are larger, heavier and more expensive. They're brighter (and usually of higher quality). ;-)