Pick up the correct specification of Ramsden eyepiece from the following :

• it consists of two equal piano convex lenses
• the curved surfaces of plano-convex lenses face each other
• the two lenses are separated by a distance equal to 2/3 of the focal length of either lens.
• the distance between the diaphragm and the front lens of the eyepiece is kept equal to 1/4 th of the focal length of a lens so that rays from a point on the diaphragm enter the eye as a parallel beam
• all the above.