Casa I am dealing with the same issue as you. Plan to use Pentax K and Pentax M42 on my XT-1 with a speed booster and wondered if you took the above advice and are going: Lens Turbo EF-X plus an M42-EF cheap adapter? And/or Lens Turbo EF-X plus an K-EF cheap adapter? Any feedback from folks in a similar situation would be very helpful! Thanks!