The potential distribution along the axis of two long equal coaxial conducting cylinders has been found to be empirically expressible in terms of the radius and separation of the cylinders. The empirical expression checks well with the single special case (zero separation) which is known to have been solved analytically. The general empirical expression, combined with the theoretical lens equation of Hansen and Webster yields an algebraic formula for lenses of this type directly relating object and image distances to readily measurable quantities.