N-BK7 plano-concave lenses are flat on one side with a precision concave surface on the other side. Plano-concave lenses bend parallel input rays so they diverge from one another making them usefully for beam expansion applications. PCV lenses have a negative focal length, so they are used for image reduction or to spread the light. N-BK7 is an excellent lens material for most visible and near infrared applications. N-BK7 is the most common borosilicate crown optical glass, providing great performance at a good value.
Production capabilities:
| Diameter available | 2mm-700mm |
| Tolerance | +/-0.02mm |
| Thickness tolerance | +/-0.05mm |
| Surface quality | 40-20 or 20-10 |
| Surface figure | L/4 or better |
| Centering | 3 arc mins or better |
| Chamfer | 0.1mm to 0.3mm |
| Coating | AR coated @ visible wavelengths, or NIR, reflective coating mirror coating for concave surface |
| Glass | N-BK7 or H-K9L |
Introduction of our manufacture specifications:
1), Diameter tolerance: The diameter tolerance of a circular optical component provides the acceptable range of values for the diameter. This manufacture specification can vary based on the skill and capability of the particular optical shop which is making the optics. Anyway, diameter tolerance does not have any effect on the optical performance of the optics itself, but it is a very important mechanical tolerance that must be considered if the optics going to be mounted in any type of holder. Normally, we make the diameter tolerance as +0/-0.1mm, for high precision requirement, we can be able to make it as +0/-0.01mm.
2), Center thickness tolerance: The center thickness of a optical lens, is the material thickness of the component measured at the center. Center thickness is measured across the whole production process. The change of the center thickness of a optical lens can affect the optical performance because center thickness along with radii, determines the optical path length of rays passing through the lenses. The highest center thickness tolerance we can do is +/-0.01mm.
3), Radius of curvature: The radius of curvature is defined as the distance between optical lenses vertex and the center of curvature. So it could be positive, zero or negative depending on the surfaces. The radius of curvature plays a important role to decide the optical path length of rays passing through the lenses, and also decide the power of the
Surface. The highest tolerance for radius we can do is +/-0.01%.
In addition, the centering and bevel are important specifications when fabricate lenses.
