What is a Power Diaphragm Assembly

I'm having a 24-70L repaired by Canon in Irvine. The diagnosis is to replace the Power Diaphragm Assembly for $460.

What is this assembly? What would cause one to be damaged or fail? Is this common with this kind of zoom lens?

Appreciate any insight as I am will to learn perhaps how to prevent it from happening again. Canon was no help with any of these questions.

Thanks,

--Geoff

Sounds like aperture? Maybe?

My 17-85 diagram assm was $27, $142 total from Canon. Probably the broken cable, but easier to replace the whole assm., rather than solder the wires. My auto focus works again.

The power diaphragm assembly is the mechanism that stops down the aperture. Any lens without a manual aperture ring has one. The assembly itself is almost impossible to damage without destroying the lens. Moisture / dust damage is the likely culprit.

Moisture? Would living in Hawaii contribute to a problem like this?

see part number: YG2-2062-000
(seems it's common to 70-200mm f/2.8 also)

gmaize wrote in post #16444545
Moisture? Would living in Hawaii contribute to a problem like this?

Bringing a lens from an air conditioned environment into a hot and humid environment repeatedly might shorten a lens' lifespan. If your lens ever fogs up that's a warning you need to take more precaution to shield your gear from sudden changes from cool to warm. I carry a couple gallon freezer bags for this purpose - if any condensation occurs it will be on the outside of the sealed bag. Being in a humid environment in and of itself won't hurt a lens, ever.

^^interesting input. We don't have AC at home, so perhaps humidity is not the contributing factor here. Thanks for the comments folks.

--Geoff

gmaize wrote in post #16443338
I'm having a 24-70L repaired by Canon in Irvine. The diagnosis is to replace the Power Diaphragm Assembly for $460.

What is this assembly? What would cause one to be damaged or fail? Is this common with this kind of zoom lens?

Appreciate any insight as I am will to learn perhaps how to prevent it from happening again. Canon was no help with any of these questions.

Thanks,

--Geoff

Here is a EMD (electromagnetic diaphragm) from an EF 35-70: https://www.youtube.co​m/watch?v=SrlPBPvHSTk

EMD (Electromagnetic Diaphragm)

EMD (Electromagnetic Diaphragm) is a diaphragm drive control actuator, which is a component integrating both a stepping motor and a diaphragm blade unit in a single unit, used for fully-electronic data transmission EF mount system. Every EF lens incorporates an EMD unit as a basic component of the EOS system. EMD controls diaphragm blade by a stepping motor and aperture diameter by electronic pulse signal from the camera body to overcome the problem of conventional mechanical diaphragm units, while also provides benefits that conventional mechanism does not offer.

High-precision digital diaphragm control is much more accurate than with conventional mechanical linkage systems. Extremely quiet operation because of no shock of mechanical levers. Compactness thanks to the integrated diaphragm control components.