Strange metering/overexposure problem 500D + 28-135IS

Hi everyone, I'm having some weird problems with my 500D and 28-135 lens drastically overexposing. Recently I had to consistently set exposure compensation to -2 to get any reasonable shots in daylight, but now it's got significantly worse.

The same lens on a 40D takes the same test scene in Av mode at 1/6 when set at 5.6 and produces a good image, but on the 500D in Av mode at 5.6, it calculates the same scene at 10 seconds which of course gives an intensely overexposed image.

My 50mm f/1.8 lens seems to work fine on both cameras, calculating speed of around 1/6 or similar for the test.

As would be expected, metering when doing Live view photos with the 500D/28-135 combination works fine.

I've cleared all settings on the 500D, I've cleaned the contacts on the camera and on the lens, but I'm running out of ideas as to where the problem may be.

Any ideas? I'll be happy to upload test photos if anyone thinks it will be of use. I'm usually pretty good at diagnosing camera problems, but this one has me baffled.

In summary:

Lens works fine on 40D
50mm lens works fine on the 500D
only problem with 28-135 lens on 500D, grossly overexposing in any mode where exposure is being calculated, eg Av or Tv
all settings reset to default on 500D, so pretty sure it's not a configuration issue.
EF lens to camera data contacts clean on both lens and body.

Jolyon

Try shooting some test shots in M mode with the faulty lens on the suspect camera. It would be interesting to confirm that the lens is stopping down as you shoot. The lens focuses wide open, then closes down to the selected aperture for the shot. If thats not happening it would cause overexposure. Shooting in M mode would take metering abberations out.

The lens seems to work fine in M mode on the 500D. I suspect the problem is more to do with the 500D than the lens (although I can't explain why the 50mm works fine) - it's not just the lens being stuck full open (the lens still misbehaves when I set it to f/3.5 - full open at 28mm)

I'm still baffled by it. The camera has about 59,000 shutter activations, has been using the magic lantern firmware, but the problem is seen whether this firmware is activated or not.
Jolyon

jolyon wrote in post #14551764
The lens seems to work fine in M mode on the 500D. I suspect the problem is more to do with the 500D than the lens (although I can't explain why the 50mm works fine) - it's not just the lens being stuck full open (the lens still misbehaves when I set it to f/3.5 - full open at 28mm)

I'm still baffled by it. The camera has about 59,000 shutter activations, has been using the magic lantern firmware, but the problem is seen whether this firmware is activated or not.
Jolyon

Might be time to ditch the magic lantern, then reinstall if you feel you need it.

Ok. to add to the picture, i rememberd I had my old 75-300 4-5.6 II lens here (i don't use it much!) - and it shows exactly the same problem with the 500D.

So the question has to be, is there any reason why the 28-135 and the 75-300 are not working correctly, but the 50mm is? The only common factor I can see is that the 50mm has a plastic mount, the other two lenses have metal mounts. Could some earthing issue related to the metal mounts be causing exposure calculation issues, or is there some other reason why the 50mm works but the other two don't?

Jolyon