Canon EOS with converted lenses- exposure issues?

Some Canon DSLR shooters report exposure issues with converted lenses. Curious if this is an issue with older EOS cameras
Thanks

I tried a Kenko 1.4 multiplier some years ago on my EOS3, and I had to dial in one stop correction to get the exposuer right.
The lens was a Sigma 300/4, I dunno if this could be the lens causing the issue.

I use a Zuiko 50mm lens from my Olympus OM camera on my digital camera and it exposes just fine. I have to set the aperture manually in Av mode and then let the EOS camera figure out the shutter speed. I haven't tried it yet in one of my EOS film cameras but it should work just the same.

I have also used my Opticron birding telescope attached to my EOS camera and that exposes just fine as well.

Film cameras often are TTL-OTF, Thru-the-Lens Off-the-film. I don't know enough about the design of various EOS film camera metering to comment on how they all do it...I know that SOME models of EOS film SLR (EOS 1n, 5, 10)do have sensors that read the film surface.
Auto exposure with dSLRs face the issue that reflectivity of the sensor surface prevents directly having photosensor pointed at the focal plane, but have to read with sensors up in the pentaprism. And stopped-down metering, in using adapted manual focus lenses on Canon dSLRs, is probably the source of the problem.

I have done extensive testing with a variety of Olympus and Tamron lenses -- both with 'chipped adapters' and 'unchipped adapters' -- adapted to my Canon dSLR, and the most accurate metering is at f/4, but as you stop down (or even open up from f/4) the metering accuracy suffers. A -1EV change in lens aperture does NOT necessarily manifest in a +1EV change in shutter speed! and -- very, very puzzling -- each adapted lens is different from what happens with another adapted lens!

http://photography-on-the.net/forum/showpost.php?p=14450413&postcount=12

Most light meters are less accurate when there is less light, so if you are using a converted lens (or any lens for that matter) in stopped-down mode, you might get less reliable results. If you have relatively stable lighting conditions, consider metering wide open before you start shooting, and then adjusting the shutter speed for the aperture you want, and as long as the light isn't changing, you can keep the same exposure setting for the whole shoot.

I used several rokkor lenses on my 1V with no metering issue at all. If I recall correctly, there was a custom function on it that had something to so with this...

Thanks
There is an issue that is documented on Fred Miranda where some digital models, due to metering through the focusing screen, meter funny
(due to the screen not transmitting more light than F2.8 or something like that and thus needs info, such as the max aperture, to deduce proper exposure)