If the distance of object and image are not measured from optical centre (C), but from first and second principal foci respectively, then newton’s formula states

{f_1}\,{f_2}\, = \,{x_1}\,{x_2} Where,

{x_1}\, = \,{F_1}\,O\, = \,distance of object from first focus F1.

{x_2}\, = \,{F_2}\,I\, = \,distance of image from second focus.

If medium on either side of lens is same, then {f_2}\, = \, - \,{f_1}\, = \,f.

So, Newton’s formula takes the form,

{x_1}\,{x_2}\, = \, - \,{f^2}


Post Author: E-Physics

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