Question

what are the sigm convention used in lenses??​

Answer 1

The sign convention used in lenses are -

1) All the distances are to be measured from optical centre of lens

2) Distances measured in direction of incident rays are taken as positive and in opposite direction taken as negative. In other words, the distances to the left of optical centre are taken as negative and to the right of optical centre taken as positive (Assuming object is at left side of lens)