PROBLEM TO BE SOLVED: To provide an image capturing optical system that allows for reducing size and cost of endoscopes.SOLUTION: An endoscope includes: a lens unit 35 comprising a lens L1 as a front group lens, lenses L2, L3 as rear group lenses, and an aperture stop 51 disposed between the front group lens and the rear group lenses an image sensor 33 covered with an element cover glass 43 an adhesive layer made of an adhesive resin 37 for fixing the lenses L2, L3 and the element cover glass 43 and a tip end portion 15 formed to have an outer diameter in a range from an effective diameter corresponding to a diameter of a circumscribed circle of an image sensor 33 substrate, whose maximum outer diameter Dmax can be diced, to 1.8 mm. A total optical length OL corresponding to a distance from a most object side surface of the lens L1 to a most image side surface of the element cover glass 43, and a metal back MB corresponding to a distance from a most image side surface of the lenses L2, L3 to a most object side surface of the element cover glass 43 satisfy a relationship expressed as: 7.0≤OL/MB≤1200.SELECTED DRAWING: Figure 3COPYRIGHT: (C)2017,JPO&INPIT【課題】内視鏡において小型化、コスト低減を図ることができる撮像光学系を提供する。【解決手段】前群レンズとしてのレンズL1と後群レンズとしてのレンズL2,L3と、その間に配置される絞り51と、を有するレンズユニット35と、素子カバーガラス43によって覆われる撮像素子33と、レンズL2,L3と素子カバーガラス43とを固定する接着用樹脂37による接着層と、最大外径Dmaxがダイシング可能な撮像素子33の基板の外接円の直径に相当する有限径~1.8mmの範囲で形成される先端部15と、を有し、レンズL1の被写体側最前面から素子カバーガラス43の撮像側後端面までの距離に相当する全光学長OL、レンズL2,L3の撮像側最終面から素子カバーガラス43の被写体側前端面までの距離に相当するメタルバックMBは、7.0≦OL/MB≦1200の関係を満たす。【選択図】図3
