Exposure Question

[ceemac]

I bought an adaptor to use my older lenses with my Canon t5i. The exposure using 2 similar lenses is off by at least a mile. Using my t5i and the Canon 50mm lens in AV, I get an good exposure of 1/13 at f5.6. With the t5i and the older 55mm lens the t5i in AV exposes for 1 sec at f5.6. Setting the t5i in manual to 1/13 at f5.6 gives me the correct exp with the older lens. The adaptor holds in the M/A pin on the old lens which puts the aperture into manual mode, so the aperture stays at whatever I set it for. Why can't the t5i meter correctly with the old lens?

 

[KmH]

Does the adapter have the electrical contacts needed between the lens and the camera for the camera to meter correctly?

 

[ceemac]

Yes it does, Keith. But it's my understanding that the contacts are to tell me when I have the lens focused properly, which it does. The camera starts beeping. I read the reviews on the adaptor which mentioned something about being able to calibrate it for focusing, but I haven't discovered how.
I just found some instructions. I don't knoow if they apply to metering, but I'll put the question on hold til tomorrow
Thanks

 

[ceemac]

OK problem solved. I found the instructions on the internet and followed them. The adaptor also needs to be programmed for the largest aperture of the lens. (in this case f2.8. ) As long as I set the camera to f2.8 and leave it there, I seem to get the correct exposure thru the full f-stop range on the lens itself. The lens can only be used in AV or manual, which is fine with me.