The fly in the lens ;)


I had to laugh out loud when I read this report by Roger Cicala on LensRentals today. It is hard to believe, but after a customer had sent back a rented Canon 24-105 L, it was discovered, during the routine inspection, that there was a fly inside the lens. 🙂 The fact that the 24-105 L is a weather sealed lens makes this story even more amusing.

Roger could not deny himself the fun of posting some pictures of the fly.


Image source: LensRentals

This fly is proof that one should not always blindly trust the manufacturer’s claims – such as “dust and splash proof ”, “weather-resistant”, etc. One has to positively study the technical specifications to find out what is actually really meant by these terms. Because, if such a big foreign object like a fly can get into the lens, what does that mean for moisture or dust? And the fly was not even stuck behind the lens in the very front or the very back, but in the focusing group – which means somewhere in the middle of the lens, behind half a dozen lens elements. Since simply taking the dead fly out was impossible, the lens had to be disassembled, re-assembled and recentered and optically adjusted. The technician needed more than four hours to do the job. Who would have thought that a small fly can cause so much trouble? 🙂


Image source: LensRentals

How the fly was able to get into the lens is easy to explain. Actually, the 24-105 L is not really sealed. It has only got one rubber seal at the mount. Dirt and moisture can get in through the open spaces around the extending tubus, the focus- and zoom-rings and the switches. These openings are, however, much too small for a fly. The fly probably found its way into the lens through the “backdoor”, after it had been removed from the camera. As can be seen in the following picture, the last lens element does not fully close off the lens. Between this element and the mount there is more than enough space.

Image source: LensRentals

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