Focusing Speed

[Anders Elm]

Hi,

I recently picked up an old X-Pro 1 to use mainly for shooting corporate portraits and weddings in documentary style. I was well aware of the cameras "sluggishness" when I bought it, but I also knew that my type of work do not require a super fast autofocus. But when i tried the camera out, I was chocked! I could not believe how slow this camera was focusing! It made my old X100 seem super fast! I was ready to put the camera in a cupboard an just try to forget about it, because it was virtually useless.  

I decided to do some more experimenting and started with changing the lens that I had been using (18-55/2.8 - if you don´t like shooting with zoom-lenses, you should try this little jewel!) and replaced it with a 27/2.8. And suddenly, I had a very fast X-Pro1 in my hand! I could hardly believe my eyes! It was so fast so it is not possible to see any difference when comparing it with my X-T1 (the 18-55/2.8 is working very well on my X-T1 - so there seems to be nothing wrong with that lens). 

So, my question is, what is causing one lens to focus very slow and another to focus very fast under the same circumstances? Can it bee some kind of "upgrading issue"? 

I would very much like be able to use the zoom-lens on the X-pro1 so any help would be much appreciated.

Regads 

Anders