Either form can be used with positive or negative lenses and predicts the formation of … 2. Sign convention for lens: Sign convention for lens is similar to that of spherical mirror. Watch all CBSE Class 5 to 12 Video Lectures here. Sign Convention for Spherical Mirror: Cartesian Sign Convention: In the case of spherical mirror all signs are taken from Pole of the spherical mirror, which is often called origin or origin point. Following sign convention is used for measuring various distances during the formation of images by lenses: All distances on the principal axis are measured from the optical center. Watch Sign Convention and Lens Formula in English from Sign Convention for Lenses and Lens Formula and Magnification here. Thin Lens Equation. Image Distance d i is the same sign as that of the object if the image is formed on the opposite side of the lens from the object. All the distances are measured from the optical centre of the lens. In numericals, we need to calculate some things likeObject distanceImage distanceObject heightImage heightFocal lengthTo calculate them correctly, we need to find whether it is positive or negativeThe sign convention mentioned below helps us in itWe can see the sign convention in … The new sign convention is known as New Cartesian Sign Convention. This way you can ignore the sign of the lens radius and simply set the sign terms ($\beta_1$ and $\beta_2$) to correct values for the particular type of lens you are studying. According to cartesian sign convention, 1. Cartesian sign conventions are used for measuring the various distances in the ray diagrams of spherical lenses. The object is always placed on the left side of the lens. A common Gaussian form of the lens equation is shown below. This sign convention is known as New Cartesian Sign Convention. 3. 2. Signs are taken left of the optical centre as negative, right of the optical centre as positive, above of the principal axis as positive and below of the principal axis as negative. This is the form used in most introductory textbooks. MIT 2.71/2.710 02/16/09 wk3-a-How to make sense of the sign conventions 11 • Recall: light propagates from left to right; therefore: • if an object is to the left of the optical element – then the distance from the object to the element is positive; • if an object is to the right of the optical element – then the distance from the object to the element is negative; Lens sign convention 1. SIGN CONVENTION. Object Distance d o is + (real) if the object is on the same side of the lens as the original object d o is - (virtual) if the object is on the opposite side of the lens from the original object . Sign is taken as – (negative) from pole of a spherical mirror towards object along the principal axis. A form using the Cartesian sign convention is often used in more advanced texts because of advantages with multiple-lens systems and more complex optical instruments. The sign convention I have applied is: $\beta_1=+1$ when left surface is convex $\beta_1=-1$ when left surface is concave $\beta_2=+1$ when right surface is concave