| 摘要 |
Four lenses having a common optical axis are provided in a lens barrel 17 composing an image-forming optical system. The four lenses are termed G1, G2, G3, and G4 from the light source side first and have positive, negative, positive, and positive components, respectively. The lenses G1 and G2 have high error sensitivities, while the lenses G3 and G4 have relatively low error sensitivities. The lenses G1, G2, and G3 are held by a first lens barrel made of metal having a low thermal expansion coefficient, while the lens G4 is held by a second lens barrel made of resin having a high thermal expansion coefficient. On the other hand, an image pickup element is held by a third lens barrel made of metal having a low thermal expansion coefficient. The first lens barrel is adhered to and held by the second lens barrel, while the third lens barrel is joined to and held by the second lens barrel. Each of the first and third lens barrels is attached to the second lens barrel.
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