The latest lenses may sometimes have bugs due to an ever-increasing reliance on firmware, but the bug Roger Cicala and his team at Lensrentals recently came across inside a 70-200 mm F2.8L IS II lens didn’t seem to be fixed with the latest Canon firmware update. That’s because it wasn’t a bug in their programming, it was a dead fly that managed to trap itself within the lens’ optical elements.
A sneaky fly somehow found its way into the deepest parts of a Canon 70-200 mm F2.8 lens, where it remained until it died prematurely. Of course, Roger and his team wanted to remove the little criterion, but not before using it as an opportunity to see just how much a fly in the lens affected a lens’ performance and share the results (and process) with the world. The blog post was written in Roger’s own words for two reasons:
“1) [To shot that] this big-ass fly had almost no effect on image quality, so that little dust speck you’re frantic about sure doesn’t, and
2) getting flies (or dust) out of a lens is a lengthy and difficult process that takes a long time.”
How well did the lens perform inside it with the fly stuck? ‘Good indeed’ according to Roger. The Lensrentals team took the time to run a full set of MTF tests and stopped all focal lengths down the lens.
As noted in the blog post, until the lens was stopped down to F13 there was no sign of the fly, but even then all that was visible was a shadow in the picture. Stopping down to F22 and zooming out to 70 mm showed a much more prominent black spot, but it only took up a fraction of the frame even then.
The rest of the post details the teardown process and shows how much effort it takes to thoroughly clean up a lens’ inner elements, especially a zoom lens as intricate as an IS lens of 70-200 mm. Head over to the blog post of Lensrentals for all the nitty-gritty details of the teardown process and more photos.
Roger’s takeaway message from the fly-laden lens image test is ‘if your dust spec is smaller than a fly (about 4mm by 1.5mm) it will not appear in your images.’ He goes on to say in the section ‘Final Thoughts’:
“I think this does serve as a good demonstration of how little effect even a very large object inside the lens has. It would have a more dramatic effect, probably, if it had been located closer to the rear element. It’s also a really good demonstration on why we (nor anyone else who’s qualified) won’t clean the dust out of your lens for $50. Sure, a lot of lenses are easier to do than this one, but it’s still time-consuming and often technically difficult.”
Regarding how the fly got into the lens, Roger deduces that it probably made its way into the lens through the small gap made in the back of the lens that can open up during the zooming process. The lens had been in the rotation of Lensrentals for 15 months, so he believes that after leaving the factory, it found its way into the lens. Roger admits, however, that he is not a bug expert, so he is not opposed to hearing other opportunities.
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