Focusing problem

HEllo group: I built this new microscope and cannot figure out why 1/3 of the image is out of focus. I have tried with different objectives, different magnifications, reposition the lenses, and the LED without success. I also tried lifting the slide from one end. This image is of a blood smear using a 40x. what could be causing the problem?

If lifting the slide at one corner* has not helped, it could be that the camera or the tube lens are not seated straight in the optics module?

(*The axes of the slide are at 45degrees to the axes of the camera)

Is only 100 steps out of focus and is always at the left of the picture regardless of how I orient the slide. May be the tube that is slightly tilted.? Is so hard to fix such a tiny artifact.