Lensrentals
Image courtesy: Lensrentals

Roger Cicala and team at Lensrentals notice that several copies of the Canon RF 100-500mm f4.7-7.1 kept coming to their warehouse with the same exact crack on one of its internal elements. They decided to investigate the cause of this mysterious, uniform cracking.

Lensrentals’ initial assumptions

At the start of the investigation, Cicala assumed the cracking was due in part to Canon’s new optical stabilization system. The new system no longer locks down like the older EF lenses. Circala theorized the free-moving parts in the lens were banding together when shipped, causing the cracks.

“In every case, when we looked through the lens, the crack moved when we shook the lens,” he writes. “So, I assumed the cracks were in the IS unit since it moves when you shake the lens.”

Lensrentals decides to take a look inside

The only way Circle could know for sure was to tear down one spare Canon RF 100-500mm f4.7-7.1 and have a look for himself. As he broke down the lens, the element he was looking for didn’t show up. It appeared the element was likely deep in the lens’ barrel.

Image courtesy: Lensrentals

“The cracked element is obviously within this assembly but we still can’t be certain which element it is, other than it’s neither the frontmost nor the rearmost,” Cicala writes. “I suspect that this entire assembly is a single part in the part catalog; that the repair center just replaces it as one piece if anything breaks in there. But we want to know what broke and perhaps find out why it broke, so we’re going to take this a bit further than the usual disassembly.”

He and the team at Lensrentals eventually was able to find the element being cracked.

“Finally, we can see that the cracked element is the one right behind the aperture assembly. That’s a thin singlet that we can tell by moving the front focusing motor manually is also the forward focusing element,” he says “There’s no possibility that this element could physically contact the one we just removed. The aperture assembly separates them and the aperture is soft and flexible, so that couldn’t have caused damage.”

No answers yet

After discovering which element was being cracked, Cicala and Lensrentals determined there was no way that element could be physically cracked by another element in the lens. That means the Canon RF 100-500mm f4.7-7.1’s free-moving design wasn’t causing the cracking.

Image courtesy: Lensrentals

“We did carefully check the movement of each element in the inner barrel with the focus motors off, etc. and there is no possibility this element impacts any other element. There doesn’t seem to be any hard stop in its travel that could cause a shock with movement,” he writes.

What’s causing the cracking?

After his investigation, Cicala still isn’t sure what’s causing the cracking.

“So why did several of these crack during shipping? I have no idea,” he writes. “My first thought, given that it’s winter, was perhaps temperature shock, moving from sub-zero trucks to warm indoors or something. But I’ve asked several people more knowledgeable than I and none think that’s a possibility. The ones that cracked are all early copies from a similar serial number range, perhaps there were some flawed elements early on.”

Considering these are earlier models of the lens, it is possible the lenses content the same flawed elements. However, that’s just speculation and not confirmed. As of now, the mysterious cracking remains unsolved. Lensrentals will continue to look at the cracking, so we’re sure the cause will be revealed sometime in the near future.

Image courtesy: Lensrentals

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