Imaging lens

An imaging lens comprising:

• a first lens group;
• a second lens group;
• and
• a third lens group, arranged in this order from an object side to an image plane side,
• wherein said first lens group includes a first lens having positive refractive power, a second lens, and a third lens,
• said second lens group includes a fourth lens having negative refractive power and a fifth lens,
• said third lens group includes a sixth lens having negative refractive power and a seventh lens,
• said imaging lens has a total of seven single lenses,
• said first lens, said second lens, said third lens, said fourth lens, said fifth lens, said sixth lens, and said seventh lens are arranged with a space between each of the lenses,
• said second lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius,
• said third lens is formed in a shape so that a surface thereof on the image plane side has a positive curvature radius,
• said fourth lens is formed in a shape so that a surface thereof on the object side has a negative curvature radius,
• said sixth lens is formed in a shape so that a surface thereof on the image plane side has a positive curvature radius, and
• said first lens has an Abbe's number νd1 so that the following conditional expression is satisfied:
• 40<νd1<75.