I only once (and then, especially for the test) did the calibration on the middle zone "M". The main "working" zones for me are "S" and "XS". Therefore, it is difficult for me to say offhand what kind of run-up comes out on large calibration zones ... Perhaps I will find time to repeat the test more carefully, at least on the "M" zone.
The accuracy itself depends on the calibration zone (the larger the zone, the lower the resulting accuracy). Also (to a lesser extent) the quality of the calibration plays a role (the value that the program shows in the main window (where the current zone and accuracy are indicated)).
According to the size of the projection and the field of view of the camera - first you need to make sure that the zoom in the projector is set to the minimum.
You also need to understand that a lens with a focal length of 12mm, originally designed for a 2/3" matrix, will have a real value of about 14mm on a 1/1.8" matrix. However, due to such "cutting", possible edge distortions of the optics are almost completely removed. The "extra" edges of the projection are really not used, but only when projecting onto a plane that is perpendicular to the camera axis. When a real object is being scanned, this size can change in the frame. Also, at the edges of the projection, the sharpness of the patterns drops a little (that's why the "cropping" of the frame helps here too).
The accuracy of the scan itself, first of all, depends on how accurately the calibration table is measured at the factory (this value is written on it). But only the detail (density of points) that the scanner can produce depends on the ratio of the projection size and the field of view of the cameras - the number of scanned points itself is (conditionally) unchanged for any size and is determined (ideally) by the number of pixels of the camera matrix (and, to a much lesser extent - on the resolution of the projector (more precisely, the density of the patterns that it creates on the object)). But the minimum distance between the points of the resulting "cloud" is directly related to the size of the object.
P.S. As a result - if you really want to "adjust" the field of view of the cameras to the size of the projection, then you can reduce the distance between the cameras and the projector, provided that they move (if you look at the attached picture) along the "red" line, and not along the "blue" ".
- Changing the distance from the cameras to the projector
P.P.S. I am currently testing 12-36mm varifocal lenses in an attempt to save on buying two extra pairs of 12mm and 25mm (in addition to the 16mm I have). Due to their large dimensions, they even had to make new adjustable mounts to increase the angle in the "XS" zone, avoiding the complete blocking of the light flux from the projector from too close lenses
- Size comparison between 16mm and 12-36
- Here the scanner is set to the XS zone