First " L" lens

[douvidl]

I've just ordered my first "L" lens, for more money than I hoped for.  I'm still in a little shock.   However, I read about folk who have gotten a "bad copy" or good copy" or have had to return the lens for re calibration.  What does it all mean?  How can you tell if your lens is "good copy",  what makes it a "bad copy".
These maybe all obvious to you all but not to us who are new at using a very expensive lens.
Thanks for you efforts
David

[JeanMichel]

Hi,
I only have one L lens, the 24-105. My other two lenses for my 5d2 are a 20 and 40 from Voigtlander. I would not worry about whether my lens was a good or bad copy, I think that there is a bit of paranoia online about this, it is probably exceedingly difficult to buy a BAD lens these days. That said, my 24-105 does require a "minus 10" in the AF microadjustment (see the other threads on this subject). That adjustment did improve the images substantially, and I suspect that you may find that yourself - it is fairly easy to do this.
Jean-Michel 

[AFairley]

The rule of thumb is that if you truly have a "bad" copy, you will know.
"First, the practical conclusion. Test every new lens you buy, right out of the box, and make sure it’s reasonable. Speaking as someone who has lots of test charts and moderately fancy equipment to do that quickly and efficiently, I’ll just say you don’t need it. Just find a couple of brick walls, fences, etc. that are in a flat plane and take some pictures. A bad problem will be evident very quickly. If the lens is bad, send it back to the store for exchange, not in to the manufacturer for repair (Because certain manufacturers are very likely to say “impact damage” and deny warranty even if you just unpacked it. No, I won’t name names, I don’t have strong enough evidence to say one does this more than another.). Which brings up another point: don’t buy anything from a place that won’t take it back. But don’t confuse the need for autofocus micro-adjustment with a bad lens, it’s not." (from lensrentals.com, http://www.lensrentals.com/blog/2010/03/this-lens-is-soft-and-other-facts

  That said, there is sample variation among lenses.  The folks at Lensrentals.com (who have a large number of samples to play with) have written about this quite a bit.

http://www.lensrentals.com/blog/2011/10/notes-on-lens-and-camera-variation
http://www.lensrentals.com/blog/2011/10/the-limits-of-variation

[JohnAONeill]

I would not sweat it if I were you. I have been buying canon L-Lenses for over a decade and so far I have never had one with any issues. I think the nature of the internet is you always hear the horror stories first and nothing about the millions of good "copies". If you want to give the lens a quick test when it arrives there are a few tests worth doing just to make sure it's not a problem lens. Check the auto focusing acuracy by puting the camera on a tripod and put a measuring tape or rule on the workbench. Angle the camera so that it is approx 45 degrees angle from the bench. Now shoot some test images and take note of the exact number that you focussed on, using the cameras auto focus. Now load the images on your pc and check to see if the actual focus point was acurate. Or was it a point in front of or behind the point?

Next take some test shots of a brick wall at every aperture and inspect the lens for sharpness across the entire image area. Most L lenses should perform reasonably well here, but no lens will be perfect. Just look out for any major issues here. IF you do find issues the feel free to post them here for a second opinion. If a lens does have problems it's best to find then soon after delivery rather than 12 months later (after the warranty has expired!)

Hope it works out for you, but as I said earlier, most L copies are decent these days ;-)

Cheers
John

[stever]

don't entirely agree.  from my experience there is little variation in the tele lenses.  However the 17-40 and 24-105 (and likely the 16-35 and 24-70) have a high probability of asymetrical performance at large apertures (in fact, i think the probability is 100% - just a matter of degree) - the tolerance issues of aligning all the glass and complex movements results in lens-to-lens variation.

my experience (and as i understand it lensrentals.com) is that Canon service (warranty or paid) can't deal with the alignments causes of asymetrical performance.  given the cost of these lenses i think it's worthwhile testing 2 or 3 copies of the wide zooms