Forums > Back > Canon 24-70 f/4L IS - Residual Spherical Aberrations?

07-29-2013, 08:59 AM

Hello Martyn,



Welcome,



Hmmm….I've been enjoying sitting back here, looking in and making no comments, and I was hoping that everyone here who are all more knowable than I, would answer this question first, so that I could remain invisible, but I have this lens so suppose that I should say something. Although I wish I didn't feel so inclined, and if you were to search my previous comments, it's all back there in ages past.



Also it might possibly be a waste of your time reading this stuff below if your camera doesn't have micro-focus. And as a disclaimer, not wanting to tread on any persons or manufacturers toes, this is my experience with my lens on my camera, a 7D. Having tried two copies roughly the same - I feel that this lens was designed to help stop my brain from ossifying out in the field and never coming back home with me.



Anyhow, quickly: I actually quite like the pictures from this lens when it's in focus….in focus exactly on what I focused on in the scene :-)



So my micro-focus settings for accurate auto-focus with this lens on my 7D are -



With f/8 being a constant 0 :



at 24mm: f/5.6 = +3. f/4 = +6 (or a tad more)

at 35mm: f/5.6 = 0, f/4 = +6;

at 50mm: f/5.6 = 0, f/4 = +3;

at 70mm: f/5.6 = 0, f/4 = 0;



Macro heads off in the other direction so that roughly 78mm and f/4 it appears to require a micro-focus setting of -6 (or more) for accurate auto focus on my camera.



So your description 'floating focus' is nice….for my lens…..using floating micro-focus.

And on a separate matter you mention, I like the Sigma, but don't take my word for it, try it yourself.



…..Why give the short answer when a long one will do to.

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