Patent ID: 8144395

Claim:
A focusing apparatus for use with an optical system having a high numerical aperture (NA) objective lens, the apparatus including: an image forming and capturing means for forming an image in an intermediate image zone, and for capturing an image by receiving and refocusing light from a selected focal plane at a position within said intermediate image zone; and a focus adjusting means for adjusting the position of the selected focal plane within the intermediate image zone, wherein the image forming and capturing means includes a first high NA lens for forming an image in the intermediate image zone and a second high NA lens at an axial position relative to the first high NA lens for receiving and refocusing light from the intermediate image zone, wherein the focus adjusting means includes means for adjusting the axial position of the second high NA lens relative to the first high NA lens whereby, in use, spherical aberration introduced by the high NA objective lens is reduced.