ok so only lasers are moved not camera distance from scanned object then right?

I also wondered how all this works when scanning large objects like 7" dia versus small like under 2" dia as to how good details would look to camera since we are basically talking Macro focus which is not like pin hole or deep field of veiw which is mostly focused full depth (or pan focus)

i think the answers to a lot of your questions will become self evident once you get your scanner working.

BTW, how far along are you on your scanner build?

I also wondered how all this works when scanning large objects like 7" dia versus small like under 2" dia as to how good details would look to camera since we are basically talking Macro focus which is not like pin hole or deep field of veiw which is mostly focused full depth (or pan focus)

The laser doesn't "focus" on the object, it simply shines a line across the model surface, that line is distorted to follow the shape of the model, and is, in turn is recorded by the camera.  Then the software does all the interpolation generating a point cloud representation of your model.

why would changing that make anything better? its like un-focusing a camers

The reason you have control over the "X" values of the left & right lasers, is becuase they tell the software the actual location of the laser with respect to the center of the camera.  the 4.95" value would be accurate only IF your scanner build (print and assembly) was perfect.  In reality, there will be minor differences from build to build, and even between the left and right lasers.

Also, some people (like the OP) might choose to design or modify their scanners, and in the process change the distance between the laser and the camera (smaller distance for a shorter, more compact machine, or longer for a larger one).  When you change the physical distance between the lasers and the camera, you need to tell the software the new value, so the interpolation is correct.