Have the ring obtained in the usual manner and faster Amazon full of anticipation tested immediately. First the positive: very well made, very stable and packed in leather bags. But immediately after that disillusionment was spreading.
I have tested the intermediate ring with the following lenses at a 7D, and my negative experiences relate almost exclusively to the autofocus. Who always focused manually, must not continue, which will have its fun with it.
18-55 EF-S IS: autofocus absolutely not available, can not find focus
28-135 IS USM: autofocus absolutely not available, can not find focus
50 EF-S 1.4: autofocus works, but backfocus
EF-S 55-250 IS: autofocus will work, but with a strong backfocus
100-400 L IS USM: Apparently you have to only spend a lot of money because of the lens works the intermediate ring excellent.
My experience was a colleague (he gave me the EF25 II recommended) not to admit and has borrowed the intermediate ring for testing. Since it has no DSLR right now, he has tested on the EOS 5. With the same results as in my test. Seems not to be necessarily just at my camera and lenses.
Accordingly, my colleague was unhappy (we wanted to buy the part together because each of us makes only occasionally Macro shots). Have returned so the ring. We will probably opt for the 100 Macro 2.8.
Other Electronics, as noted in another review, works perfectly (light meter and iris) Unfortunately I can not say that the AF.
All told, my rating accordingly unfortunately only 3 stars:
Price: -1 star because third party offering such intermediate rings significantly cheaper.
Autofocus: -1 star
Normally, however, we are both focused on Canon products, in this case, unfortunately not.
