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Old 19-10-2010, 12:26 PM
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dugnsuz (Doug)
to baldly go...

dugnsuz is offline
Join Date: Aug 2005
Location: Hahndorf, South Australia
Posts: 4,201
Originally Posted by Martin Pugh View Post
Doug - So, let me understand clearly. The 70-200 f4L IS USM lens is a much better performer than its f2.8L equivalent?
Questions: Why did you opt for the more expensive IS version - is IS really necessary when the lens is used for astrophotography?
The range in order of performance/sharpness (as reviewed by daytime photographers)...
1. 70-200mm f2.8L IS
2. 70-200mm f4L IS
3. 70-200mm f4L
4. 70-200mm f2.8L

I went for the f4L IS as I wanted a very good daytime lens too where the IS will be handy.
The 2.8L IS was out of my price range and all reviews of the f4L IS found it be very sharp from edge to centre. MTF performance (pic below) at 135mm and 200mm is almost comparable with the equivalent primes
Kind of counter-intuitive in a way due to the extra lens elements used for the IS - one would think it would be less sharp than it's non IS sibling, but it's consistently reviewed as one of the sharpest zooms out there.

As you've stated, the IS circuitry is useless for astro work and should be turned off.
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