I was intrigued by the data that Roger Cicala posted at LensRentals.com. He says that the 40 pancake is one of the new batch of Canon lenses that have a more accurate autofocus system which can be used to good advantage by the 5D III and 1Dx. Since they are now going for only $149 I decided it would be an inexpensive way to check out the advantages of the new technology. Got it a couple of days ago.
I immediately started putting it through my usual focus tests to see if it needed some MFA and just how consistently it focused. (MFA is not very helpful if a lens does not focus consistently.)
With the lens on my 5D3, I found that it back focused about one foot at ten feet. I call that 10% back focus. However, about one shot in five was significantly front focused, maybe 5%. I changed my working distance and the focus error changed. Grrrr....
I tried adding some MFA, but the point of final focus was too inconsistent for me to want to use the lens wide open.
I'm sending it back for another copy. Will keep you posted on the next one.
All of my other lenses work great on the 5D3. This is the first reject. Too bad, cause it's a cute lens.