Optical system for endoscopes

DETAILED DESCRIPTION A primary object of the present invention is to provide an imaging optical system for endoscopes capable of forming an image free from the color shading even when the solid-state image pickup devices comprising the mosaic filters are used.
The optical system for endoscopes according to the present invention has the fundamental composition illustrated in FIG.
2 wherein a field lens component L.
sub.
F is arranged on the image side of an imaging lens system L.
sub.
M comprising an aperture stop S and a solid-state image pickup device is arranged on the side where rays emerge from said field lens component L.
sub.
F.
Further, the optical system for endoscopes according to the present invention is so designed as to satisfy the following condition (1): f.
sub.
F <10f (1) wherein the reference symbol f.
sub.
F represents focal length of the field lens component L.
sub.
F and the reference symbol f designates focal length of the optical system as a whole.
By selecting the composition described above, the optical system according to the present invention is so adapted as to allow the principal ray to be incident nearly perpendicularly on the image surface thereof and therefore capable of preventing the color shading from being produced.
If the above-mentioned field lens component L.
sub.
F has too long a focal length, the optical system will have too long a total length and too large an outside diameter, thereby being unsuited for use with endoscopes.
In order to make the optical system compact as a whole, it is desirable to design the optical system so as to satisfy the above-mentioned condition (1).
If the condition (1) is not satisfied, the optical system will undesirably have too long a total length and too large an outside diameter.
The optical system for endoscopes according to the present invention comprises the field lens component L.
sub.
F arranged on the image side of the imaging lens system L.
sub.
M comprising the aperture stop and is so designed as to satisfy the condition (1)