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LENSES: Facts and Fallacies - Part XI
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PostPosted: Mon Apr 21, 2014 3:25 pm    Post subject: Reply with quote

Nordentro wrote:
I speak in general. The Canon 200-400mm f/4 you refer to is only a meassured 6.9 lens.


I think you are talking about the T-number of the Canon 200-400mm F4. Note that the T-number 6.9 was measured with the extender ON!

The F-number is F5.6, so the loss is little more than 1/2 stops (0.6 stops to be exact). In comparison, the prime 50mm F1.4 loses 0.39 stops. That is, the zoom loss is about 0.2 stops higher than the prime. Not bad for a zoom with 33 elements, compared with a prime with only 7 elements.


PostPosted: Mon Apr 21, 2014 11:07 pm    Post subject: Reply with quote

Yes, mesured is always T stops and F stops is the theoretical speed. As you say, with the extender is 6.9T and 4.7T without. I have no doubt about this being a fantastic lens.


PostPosted: Thu Apr 24, 2014 1:44 am    Post subject: Reply with quote

Okay, so we have the fantastic Canon 70-200/2.8 with nice sweet zoom spot at 200mm -- i.e. designed to be best at maximum zoom, where most users will set zoom...and... the fantastic Sony 14-24mm, along with something or two from Zeiss. What other newer zoom lenses are there which are better than primes.

I will concede that a few modern zoom lenses give as good or better performance at a sweet zoom spot than corresponding prime, but that leaves the entire remaining zoom range...can we say that Canon 70-200mm/2.8 gives as good or better performance at 135mm, at 85mm? No.