# Sweet spot for 17-40 f4 L



## Prophet (Dec 27, 2008)

Maybe this isn't an appropriate question, but anyone know where the sweet spot is for the 17-40 f4L and shows the best performance. I read that almost any lens performs best 2 stops up from the bottom. That would be about f8 on this lens, correct? Given a scene with appropriate light, can anyone tell me what a good point to get the best photo's? 

I think I'm going about things the wrong way... but I'm just trying to refine a few things.

Thanks,

-JD-


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## tsaraleksi (Dec 27, 2008)

The 17-40 is quite sharp starting at f/4, but I've found that a 'sweet spot' is probably f/5.6-8.


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## keith204 (Dec 27, 2008)

yep I haven't done any exact testing specific to thsi, but I recall shooting at f/8-f/11 on the 17-40L and noticing remarkable sharpness that I'd not witnessed before.


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## Prophet (Dec 27, 2008)

is that "or" or "through"?

-JD-


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## rufus5150 (Dec 27, 2008)

keith204 said:


> yep I haven't done any exact testing specific to thsi, but I recall shooting at f/8-f/11 on the 17-40L and noticing remarkable sharpness that I'd not witnessed before.



In _Understanding Exposure_, Peterson explains why just about any lens will be its sharpest at both F8 and F11, but I can't recall the specifics at the moment (nor can I quote because the book's out on loan). Made sense from an optics perspective, though. Many lenses have sweet spots of extreme quality but with a wider aperture. The 17-40 I used for exactly a day was amazing at 5.6 and a tad soft wide open.


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## soylentgreen (Dec 27, 2008)

Best to check the MRF charts for the lenses since they are tested wide-open. That will give you an inkling as to where the lens stacks up. The premium lenses; in general, perform just as well wide-open as stopped down. I can live with my L's wide-open and only notice a slight performance boost stopped down. As long as there is enough light or you are shooting with a tripod, stopping down does not hurt, expecially for landscapes.


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## Prophet (Dec 27, 2008)

Thanks guy for the patient and good advice. I figured some old cow would come in here to chew some cudd...... class act from all.... 

-JD-


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## Big Mike (Dec 29, 2008)

I've been told by more than one 'old pro' that lenses are sharpest at F8.  Sounds good to me.  

I also subscribe to the theory that most lenses are sharper at 1-2 stops down from wide open.  

I think this is also an issue of lens quality.  For example, most 'kit' lenses are poor when wide open but can be quite decent at F8 or F11.  A pro lens will be good (even excellent) when wide open and maybe a little better when stopped down.  I've heard that some lenses (telephoto primes) are designed to be at their best when wide open, because that is where they will be used most of the time.


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## Garbz (Dec 29, 2008)

Where the lens is sharpest? f/5.6 at the border and f/8 at the edges for all focal lengths. This can be found on any halfway decent review of this lens like at photozone.de

But where this lens performs best is at exactly the focal length and aperture you need to get the picture. Even if there were a difference between apertures or focal length which is remotely noticeable that's no reason to not get the photo you want.

There's nothing worse than a sharp image of a fuzzy concept. -Ansel Adams


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## Muay_Thai_Dan (Dec 29, 2008)

what big mike is saying is true....i have a 17-85 kit lens (canon)...and i recently noticed, how much sharper it is at f/8 when i took a few pics at that aperture not too long ago (not to test the sharpness, but i just wanted to have a deeper DoF).and when i uploaded the pics on the comp, i saw a big boost in sharpness....and from that, i concluded the same, that at f/8, its sharper/the sweet spot


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## JustAnEngineer (Dec 29, 2008)

With the 30D, you can go up to f/10 without worrying about diffraction affecting your sharpness.


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