jdben622 wrote:
Hmmm. Maybe I'm missing something. With the 2.8 in IS you theoretically get 3 more stops whereas the 4.0 IS gives you 4. If IS is employed, won't the available/useable ISO's and shutter speeds be the same for both lenses?
no you would still have twice the shutter speed with the f2.8 regardless of IS. With 4 stops IS you move into blur due to subject motion instead of camera shake.
Example. Light condtion @max ISO allows shutter speeds of 1/250 at f/2.8
at f/4 you need 1/125 (you 1 stop IS still allows for sharp images)
if 1/125 @ 2.8 (your 1 stop IS still allows for sharp images)
then 1/60 @ 4 (your 2 stop IS still allows for sharp images)
1/60 @2.8 (your 2 stop IS still allows for sharp images)
1/30 @ 4 (your 3 stop IS still allows for sharp images)
1/15 @2.8 (your 3 stop IS still allows for sharp images)
1/6 @4 (your 4 stop IS still allows for sharp images)
But at those slower shutters you worry about motion blur!
jdben622 wrote:
Wouldn't a better debate now be between f4 IS and 2.8 IS? The f4 IS is only $150-200 more new than a decent 2.8 non-IS used, and I think you'd be hard- pressed to come up with many advantages of the 2.8 non over the 4 IS. On the other hand, it's easy to come up with quite a long list of advantages of the 4 IS over the 2.8 non.
The f/4 & f/2.8 shouldnt be competing lenses. They are for different purposes even though then run about the same price. But if you ask for advantages, the f/2.8 has a major advantage over the f/4...1 full stop of light! Other advantages include better use with a TC (ties in with the aperature difference) and autofocus. Of course the f/4 has a major size advantage for travel as well as the IS. Image quality is really a wash btn the 2.
Mark Jankura wrote:
Go with the IS. I had the same question before I bought mine a couple of weeks ago. I don't think I've had a bad shot yet even with a 2x TC at 400mm I can still hand hold at low shutter speeds.
I own both the IS and non IS version and I dont think I've had a GOOD shot yet with the 2x TC
