Hello,

About two weeks ago, I started getting overexposed photographs on my rig (1dm4+500mm.) Way overexposed. First I thought it was the shutter, but after much troubleshooting and checking,
I have nailed it down to the lens.

It will not stop down properly. it works fine at f4.

For example, if I meter and shoot at f/4+ 1/4000 sec it comes out fine. Then for more DOF I shoot at f/5.6 + 1/2000 - and it is overexposed. Then I use f/8 + 1/1000 and it is WAY
overexposed. And so on... (similar results across 1dm4, 7dm2 and 6d)

Has anyone encountered this problem - is it a common one? I am going to have it looked at tomorrow. But repairing will probably entail sending it all the way to Singapore (I am in
Dhaka Bangladesh with limited Canon repair facilities.) and a long wait not to mention $$.

Are there long lead times on parts of this lens? (I noticed a diaphragm assembly in the partslist, but at this point it is too early for conjectures...)

It is out of warranty and I have shot perhaps 20000 pictures with it in the last 2.5 years.

If anyone has encountered this problem please let me know.

Many thanks,
Ihtisham