Retrofocus-type objective for an endoscope

A retrofocus-type objective for an endoscope comprising a first lens component comprising a negative lens, a stop, a second lens component comprising a positive meniscus lens arranged to be concave toward the object side, a third lens component comprising a positive lens, a fourth lens component comprising a cemented doublet consisting of a positive lens and a negative lens, and a fifth lens component comprising a positive lens in the order from the object side, said retrofocus-type objective being arranged to be focused by advancing said third lens component and said fourth lens component and, moreover, to fulfill the conditions (1) and (2) shown below:

• ##EQU3## where reference symbol f.sub.1 represents the focal length of the first lens component, reference symbol f.sub.2 represents the total focal length of the second through the fifth lens components, and reference symbol f.sub.a represents the focal length of the lens system as a whole when focused on an object at a short distance,
• said objective further satisfying the following conditions:
• D/f.sub.a <0.7 (3)
• where reference symbol D represents the airspace between the first and second lens components,
• and further fulfilling the conditions (4), (5) and (6) shown below:
• ##EQU4## where reference symbol r.sub.1 represents the radius of curvature of the surface on the object side of the first lens component, reference symbol r.sub.4 represents the radius of curvature of the surface on the object side of the second lens component, reference symbol r.sub.6 represents the radius of curvature of the surface of the object side of the third lens component, and reference symbol r.sub.10 represents the radius of curvature of the surface on the image side of the fourth lens component.