I have several M42 mount vintage lenses and I bought on eBay several different brands of adapters to be able to use them on my Olympus cameras. I like the "two-tone" adapters (the body is black, the mounting ring is silver) where I can align the position of the lens once screwed onto the adapter to match the camera. There are 3 small grub screws that allow the rotation of the silver ring and then can be secured into position once the desired alignment is achieved. Recently I also ordered a Fotga brand adapter and found that is too short. When measured against my other two brands of M42 adapters it is 1mm shorter. Fotga on the left, other brand on the right I am not too impressed with this as it puts the infinity focus on the vintage lens nowhere near the markings on the lens. On the other two adapters I can be pretty close to infinity to what the marking says on the lens. I usually achieve infinity just a bit back from fully retracted and I believe that is perfect, since some M42 lenses are not exactly "true" to their markings. With the Fotga adapter tho I have to back off my focusing a long way; on a particular lens I read 3m instead of infinity. That is approximately 60 degrees turn of the barrel to get there.