An Unlikely Intruder: The Fly Inside a Professional Canon Lens

An Unlikely Intruder: The Fly Inside a Professional Canon Lens

What seems like it could have been an April Fools joke if it had come out a few days sooner, the Lensrentals blog has posted a great (and enlightening) story on something that apparently has happened more than once: somehow, for some reason, a full-sized fly got into a lens, and the entire lens had to be disassembled to remove it. The question is: did it affect image quality?

It’s a situation that’s just plain unexplainable. A fly — yes, what appears to be a fully grown, common housefly — somehow found its way into the inner workings of a Canon 70-200mm f/2.8 IS II lens rented out be Lensrentals. An obvious first thought is that somehow, the fly entered the lens during manufacturing. But, as they point out, this particular lens had been in service for Lens Rentals for over 15 months, so it had to have gotten inside the lens after they purchased it, unless no one had noticed during that time, which is doubtful. The best theory they (and I) can come up with is that a small maggot found itself on the lens, crawled in through the rear element, and settled somewhere in the middle of the lens where, somehow, it had enough food to grow to full size before perishing in an image-stabilized graveyard. Or maybe flies are more flexible than we think, and she just squeezed in there. Who knows.

Image via, 2019.

So begins a twofold saga: what effect this fly had on image quality, and how complicated is it to remove something like this from a modern lens?

According to Lens Rentals’ testing, the fly actually had very, very little effect on image quality until they stopped the lens down to about f/13, at which point, you could start to see a dark shadow on the image. When the lens’ aperture was opened more, you couldn’t see much of an effect. 

Image showing the aperture opened up and essentially zero effect on image quality from the fly. An entire fly. Image via, 2019.

When stopped down to f/13, you could see the shadow of the fly. Image via, 2019.

This is fascinating on so many levels, and is, for me, a little vindicating. I ditched my lens caps years ago for one main reason: speed. I’m OK with my glass getting a little dustier or dirtier for the sake of speed. When I’m shooting an event and want to switch lenses, I don’t have the time to take lens caps off of one lens and put them back on the other before taking my next shot. It slows me down considerably, and the effect that a little extra dust on the lenses has on my final image is close to nothing. Enter the fly. If a full-grown fly inside the lens has such little effect, can you imagine what a few specks of dust on the elements will do? Zilch. Nada. 

Vindication at its finest.

The other part stressed in their blog post is this: it’s pretty difficult and labor-intensive to disassemble a lens to clean it. I’m guilty of getting a bill or two back from Nikon for a simple cleaning and being incredibly annoyed at the high cost, but seeing how much this lens had to get disassembled just to clean the elements (or in this case, remove an insect) was enlightening. The newer the lens is, the more sensitive electronics, elements, parts, pieces, and gizmos need to be removed and reassembled flawlessly in order for it to work again. It took over three hours and lots of experience and expensive equipment to do it. It’s certainly something I don’t even want to think about trying myself.

No beard nets required when you're dealing with flies. Image via, 2019.

Image via, 2019.

Do you have any lens repair stories that give you the creepy crawlies?

Stephen Ironside's picture

Stephen Ironside is a commercial photographer with an outdoor twist based in Fayetteville, Arkansas. While attempting to specialize in adventure and travel photography, you can usually find him in the woods, in another country, or oftentimes stuffing his face at an Indian buffet.

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Oh crikey, that is hard to explain. Almost impossible that it would've got in during manufacturing because they are anal obsessive about a clean environment and products go through extensive QA. As a larva (yew, maggot) or egg stage maybe? Obviously it got in there somehow.

Oh, I know. It slipped in through the extreme aperture. That's a warning to us all. From now on, shoot only fully stopped-down.

Easier to explain are the whiskers.

The rear element of this EF lens, if it is like most other zoom EF's then it will retract when zoomed in or out, leaving enough clearence for a fly to get in.
You just have to leave the lens uncapped and zoomed to some degree to allow for the fly to get in, specially if you're shooting landscape on some remote place filled with insects.
As a larva or egg, I wouldn't believe that, without moisture and food, the larva would just die off.

I once found a second hand Nikon 28-105mm zoom lens which the previous owner clearly stated that it had been infiltrated by fungus. For the bargain price of 20 AU$ I thought it was worth the experiment!

Upon receiving the lens I opened and removed as much of the fungus that was easily accessible but was reluctant to delve deeper into the lens for what seemed to be small traces of fungus. Having brought it to an acceptable state I closed it and placed it overnight in the safe where we kept the physics radioactive sources at the school where I worked. A Cesium gamma emitter placed on the top element had the effect of killing the remaining fungus so at least it would not spread further. What was left was hardly visible unless stopped down to f/18. Not the perfect lens but for $20 a good deal I would say! 8 years later the lens is still in good condition and used by my 18 year old son.