17-40L lens will not focus distant objects

[mcollier]

<p>My 17-40 lens will only focus foreground features. I have used this lens for several years with no problems. It does not matter what Fstop I use, whether it is auto or manual focus or if I use one or all focus points. The foreground is crisp and clear. Anything beyond a few hundred yards is lost. It is not the camera, I have several and the problem exists with all. I do not remember banging or dropping it, but it seems the calibration may be lost. I have cleaned the contacts. I will take it for service, but I doubt it will be worth it to fix. Any ideas?</p>

[alan_bryant1]

<p>The hyperfocal distance - ie, the distance which effectively becomes infinity - is quite close with that lens. In full frame it's only 44 feet away; on crop frame it's 70 feet.</p>

<p>So "Anything beyond a few hundred yards is lost" is rather confusing. Post a sample?</p>

[Ken Katz]

I would compare the results using the 17-40L and another lens at the same focal length, aperture & shutter speed, using the same camera and focusing at distant subjects. Review the files and see if there is a material difference in sharpness between the 17-40 and the other lens. Hopefully you have a comparable lens to use, like a 24-70 or 24-105. Assuming the 17-40 has a mechanical problem, given the cost to replace the lens it may very well pay to send it Canon for repair.

[Marcus Ian]

<p>Commonly with USM lenses, this is a matter of some debris jamming the focus elements movement. This should be able to be confirmed by watching the distance indicator. If it never focuses beyond a certain point on the scale, you know you've got a problem. Manual focus does not give a strong indication of a blocked path since it is a FTM USM lens (whereas with a DC motor, you have a solid indicator). Check your distance scale first. I assume that some change in focus point is occurring in AF (ie the AF is activating) - indicating that the USM is functional.</p>

<p>With this lens, if something simple is the source of the problem, the repair is likely to be cost effective. Usually the only time it climbs above 'cost effective repair' range is when they are replacing major components. If the AF is operating, then likely it will not need replacement (though maybe it will?).</p>

[JeffOwen]

<p>Is it the same at all focal lengths and if you use live view and manually focus do you have the same issue?</p>

[sarah_fox]

<p>A few hundred yards is effectively infinity on a wide angle lens. I can't imagine how a few hundred yards would appear in focus, while maybe a few thousand yards wouldn't. I, too, would want to see a sample.</p>

<p>That said, PERHAPS more distant objects are blurred/distorted by heat refraction? (It's that time of year, at least north of the equator.) A time exposure with heat refraction could render very distant objects "blurry."</p>

<p><img src="http://www.graphic-fusion.com/miscpics/springweirdness02.jpg" alt="" width="700" height="435" /><br>

"painterly" effect of heat refraction on a distant Navy play-toy</p>

[museebfoto]

<p>I agree with what has been put forward by <strong>Sarah</strong>, she pointed an important issue rarely mentioned.</p>

[david_henderson]

<p>Assuming that the lens will physically focus on infinity, does it deliver accurate focusing on close objects- ie does an object 1.5 feet away appear critically sharp with the lens set to that distance? There's a marker for that distance on your lens barrel, which is why I chose it.</p>