Similar to plano- concave lenses, a bi-concave lens diverges parallel input rays and has a negative focal length.

It has a virtual focus at the object side of the lens. Bi-concave lenses are usually suitable for absolute conjugate ratios closer to 1:1.

• Material:                          BK7 grade A, fine annealed
• Focal Length (f'):             ±2% at 587.6nm
• Diameter(φ) Tolerance:    +0.0/-0.20
• Center Thickness(Tc):      ±0.1
• Centration:                       3′
• Form Error:                     1~5 fringes
• Irregularity of Fringes:      0.2~0.5 fringes
• Surface Quality:               60-40 scratch-dig
• Coating:                          1/4 wave MgF2 coating at 550nm for 0° angle of incidence
• Clear Aperture:               90% diameter