Concave lens – radius of curvature (`R`)
We should all know what a radius of a sphere is, so it should be easy to remember that:
The "radius of curvature" of a concave lens is the distance between the centre of curvature (`C`) and the curvature of sphere.
There are two radii of curvature for a concave lens, as below.
![](/images/user/base/Maths/Logarithms/Reference%20Tables/reference-log-table-1.4df6ee6.jpg)
![](/images/user/base/Maths/Logarithms/Reference%20Tables/reference-log-table-2.d516bb3.jpg)
![](/images/user/base/Maths/Logarithms/Reference%20Tables/reference-anti-log-table-1.b0b0513.jpg)
![](/images/user/base/Maths/Logarithms/Reference%20Tables/reference-anti-log-table-2.f89189d.jpg)