David,

What video format were you shooting at, and at what shutter speed?

I had the same issue as yours last time (although mine was constant flickering), when my setting was at 720p 24fps, and my shutter speed was at 1/100. I switched it to 1/50 and it seems to fix the problem.

Some people in the forum have mentioned that it's best to set the shutter speed at two times the value of your frame rate - 24fps at 1/50, 25fps at 1/50, 30fps at 1/60 and so on, although i'm still not very clear about its relationship.

Jimmy,

The video format is MOV. as specified by the camera. The shutter speed does not affect the chance of appearance of flickering.

It happens only when I start the zooming and ends when I stop zooming. It happens outdoor and indoor.

The video does NOT darken in M mode even when the lens was facing the sun or when I moved from indoor to outdoor. But it immediately flickers once I turn the zoom ring.

Hi David, the fact that it didn't shift your exposure when you disengaged the communication between the lens and camera demonstrates that it shifts because this lens is not a continuous aperture lens. [sorry if that isn't the right term]. It has a range of f/4 to f5.6 for example.

If the the camera is allowed to communicate with that lens it will always shift its aperture to correspond to the correct focal length even with everything set to manual exposure.

There are two ways to correct this, first use this lens with it rotated slightly so there is no communication with the camera body, everything will be manual. Second use a lens that has a constant aperture.

Other than that I think that everything is working as it should, there really isn't anything to fix.

I hope this helps.