Yes, there are three adaptors,
One for 50 and 75mm framelines (no 75 on the M4)
One for 35 and 135mm
One for 28 and 90mm (no 28 on the M4)
There are different brands, I use the CV adaptors sold at Cameraquest. They are very well made and have never given me problems. You can find original Leica adaptors, and cheaper China made ones. Some folks have had no problems at all with the less expensive ones, other have had issues. And so on and so forth.