Question

Sign convention of spherical lens.

Answer 1

for concave lens:
focal length = (-)
position of object =(-)
position of image =(-)

for convex lens:
focal length= (+)
position of object =(-)
position of image=(+)

Answer 2

Sign convention for spherical lenses....

All distance are measured from the optical centers of the lens....
The focal length of a Concave lens is negative. The distance of the object is negative but the distance of a real image is positive.........