Canon EOS REBEL T2i / 550D Firmware Update (http://web.canon.jp/imaging/eosd/firm-e/eosdigital7/firmware.html)

Firmware Version 1.0.8 incorporates the following fixes.

1. Fixes a phenomenon in which the set aperture moves unexpectedly when shooting movies in manual exposure mode using some Canon lenses (such as macro lenses).


Don't know how many people have experienced it but now there's a fix.

You know I thought it was just the display that was changing brightness I didn't know it was the actual video. Go figure.

I havent really experienced this...though I am using a manual focus lens..

I just uploaded test video of old vivitar 28mm 2.8 and you can see it very clear weird dark flickering going on.

Vivitar 28mm f2.8 on Vimeo

^ Your adapter having a focus confirmation chip is what is causing the weird exposure flicker in your clip. Use an adapter without a FCC.

Adapter does have a FCC. At the moment this is only adapter I have. I get one without FCC.
Thanks

Just cover the contacts with electrical tape.