Canon EF 300mm F4 L IS USM Error 01 – Oil in Diaphragm Unit

Today we will analyze this interesting repair we just did:
The cleaning of the diaphragm group due to Canon EF 300mm F4 L IS USM Err 01

The Problem

Our client has a Canon EF 300mm F4 L IS USM, after several years of honorable career, it start giving problems for unknown reasons. At first during a photo session it started to overexpose all the photos, then after a while the lens started giving err 01 on the camera. First every now and then, and later more and more often. Turning off and on the camera the error was going away, but after a little while was there again..

When the client told us what happened we quickly came to the conclusion that there was something wrong with the diaphragm group. In fact, in our experience, in 90% of cases the error 01 on the camera is due to a malfunctioning of the diaphragm unit.

The estimate quote, without having seen the lens yet, was quite high, it was around 300€. This is because the new diaphragm group on this type of lens is really expensive.
We communicated everything to our client, also telling him that we would check everything once the lens arrived in the lab to make an accurate estimate.

The Fixing

As our practice, we always try to examine all the hypotheses in the actual estimate phase, to try, when possible, to repair the non-functioning component and not, as many do, simply replace it.
In this case, after disassembling the diaphragm group, we quickly realized that the problem was not the diaphragm unit itself, but the fact that there was oil between the diaphragm blades. The oil was blocking the usual movement of the diaphragm group, no longer allowing closure when requested by the engine of the lens.
For this reason to repair the lens we only had to disassembly all the blades, clean them all and the reassembly everything in the correct position.

The Result

In this way we were able to get the Canon 300mm F4 L IS USM working perfectly again. The diaphragm group now opens and closes precisely and quickly. Now the lens works perfectly fine and no longer shows any type of error. As always, before returning it to the client, we tested all the other components to verify full compliance with the factory specifications.
Fixed lens and happy customer because he saved a lot more then the initially expected cost!

Canon EF 300mm F4 L IS USM Repair