Lens assembly and imaging device

1. A lens assembly comprising:

a plurality of lenses; and

a lens holder accommodating the plurality of lenses and having an opening in each of a front end face of the lens holder and a rear end face of the lens holder,

wherein the opening of the front end face has a smaller diameter than an outer diameter of a foremost lens accommodated in a foremost end face side of the lens holder,

the lens holder includes a spacer ring disposed on a rear side of a rearmost lens accommodated in a rearmost end face side of the lens holder, the spacer ring abutting on a peripheral portion of the rearmost lens to keep a space between a rear face of the rearmost lens and the rear end face of the lens holder, and

the lens holder holds a rear face of the spacer ring by thermal caulking.

2. The lens assembly according to claim 1 , wherein the lens holder has a plurality of reference planes in the rear end face of the lens holder, the plurality of reference planes intermittently surrounding the opening of the rear end face and serving as a basis for optical position adjustment of the plurality of lenses, and the lens holder holds the spacer ring by thermal caulking between the reference planes.

3. The lens assembly according to claim 1 , wherein at least the rearmost lens is a plastic lens.

4. An imaging device comprising: a lens assembly according to claim 1 ; and an imaging element.