Focusing a telescope with a diameter like mine with a CCD camera attached has always been a challenge and consuming time.
To improve this critical step I decided to build an Hartmann Mask.
Internet enabled me to find a solution rapidly.
My Hartmann mask (also called a focusing mask) is an essential mean to focus my LX200 GPS. It's made of a disk of light wood with a diameter near the size of the telescope.
There are four holes placed on opposite sides with an angle of 90° each, to let the light go through. The holes sizes do not matter at all.