Scanning lens, scanning device, and image forming apparatus including same

A scanning lens to scan a document image, comprising:

• a lens;
• and
• a retainer to retain the lens bonded and fixed to the retainer by an adhesive,
• wherein:
• 0
• ≤
• 
• α
• large
• /
• α
• small
• ×
• (
• ∑
• i
• n
• ⁢
• Vp
• i
• -
• ∑
• i
• n
• ⁢
• Vm
• i
• )
• /
• (
• ∑
• i
• n
• ⁢
• Vp
• i
• +
• ∑
• i
• n
• ⁢
• Vm
• i
• )
• 
• <
• 3.5
• ⁢
• ⁢
• (
• i
• =
• 1
• ,
• 2
• ,
• …
• ⁢
• ⁢
• n
• )
• and
• 0
• <
• Vb
• /
• Va
• <
• 0.5
• and
• 0<Vb/Va<0.5
• Where
• ∑
• i
• n
• ⁢
• Vp
• i
• is a total volume of an adhesive protruding in a positive direction of a main scanning direction beyond a bonding portion between the retainer and the lens at at least one bonding location, at which the lens is bonded to the retainer by the adhesive, the main scanning direction including the positive direction and a negative direction opposite to the positive direction,
• ∑
• i
• n
• ⁢
• Vm
• i
• is a total volume of an adhesive protruding beyond the bonding portion at the at least one bonding location in the negative direction,
• i is a number of bonding locations,
• αlarge is a greater linear expansion coefficient between a linear expansion coefficient of the retainer and a linear expansion coefficient of the lens,
• αsmall is a smaller linear expansion coefficient between the linear expansion coefficient of the retainer and the linear expansion coefficient of the lens,
• Va is a volume of the adhesive in the bonding portion between the retainer and the lens at the at least one bonding location, and
• Vb is a volume of the adhesive protruding beyond the bonding portion toward the lens at the at least one bonding location.