Shimul's Diamond rule of image formation

A new pedagogical approach for predicting image formation of all lenses and mirrors is proposed, named Shimul’s Diamond Rule. The method provides a geometric mnemonic using a diamond-shaped diagram with three real arms and one virtual arm. By drawing a horizontal line from the object’s position, the intersection with the corresponding arm predicts whether the image will be real or virtual, its orientation, and relative magnification. Comparative analysis demonstrates that the rule is fully consistent with the Gaussian lens/mirror formula 1/f = 1/v - 1/u