Quote:
Originally Posted by gregbradley
F4 is starting to get a bit slow for 30 second images but for 90 second exposures they should be fine. Canon 70-200 F4L may have too much CA wide open. Not 100% sure about that. The F2.8 model may be better there or the later F4L IS version.
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The three versions are practically identical at f/4 onwards, CA is low at f/4. IMO the f/2.8 version is a bit too light greedy, at least on a full frame, and vignettes horribly wide open. A couple of minutes is the charm at f/4.