Convext lens focal length: around 10cm /5CM Convext lens diameter: about 3.5cm Optical Experiments Can Be Conducted Convex lens imaging Warning 1. Adult supervision required ! 2. Please do not look directly at the F light source, the light is strong !! 3. Please use the pry bar in the box to open the battery compartment cover to prevent scratching your nails Attention 1. NOT include battery!!! Please buy two pieces of AAA batteries yourself. We cannot ship battery internationally for safety reasons. 2. There may be slight scratches on the lens caused during the production process, which do not affect the experimental use at all. But if you mind, please do not purchase. 3. This is a children's toy for display purposes only. The lens focal length may have errors and cannot meet professional requirements. Due to different batches, there may be differences in product appearance and printed text, which will not affect use Colour:As Shown Material:plastic Package Contents: 1 * Optics Experiment Kit Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.