Image capturing optical system, image capturing device and electronic device

An image capturing optical system, comprising five lens elements, the five lens elements in order from an object side to an image side comprising a first lens element, a second lens element, a third lens element, a fourth lens element and a fifth lens element, each of the five lens elements comprising an object-side surface facing toward the object side and an image-side surface facing toward the image side;

• wherein the third lens element has positive refractive power, the object-side surface of the fifth lens element is concave in a paraxial region thereof and the image-side surface of the fifth lens element is concave in a paraxial region thereof, and a central thickness of the first lens element is the largest among central thicknesses of all lens elements;
• wherein an axial distance between the first lens element and the second lens element is T12, an axial distance between the second lens element and the third lens element is T23, an axial distance between the third lens element and the fourth lens element is T34, an axial distance between the fourth lens element and the fifth lens element is T45, half of the maximal field of view of the image capturing optical system is HFOV, a maximum index among the indexes of the first lens element, the second lens element, the third lens element, the fourth lens element and the fifth lens element is Nmax, a focal length of the fourth lens element is f4, a curvature radius of the image-side surface of the third lens element is R6, and the following conditions are satisfied:
• 0.25<T12/(T23+T34+T45);
• 0<tan(HFOV)<0.45;
• 1.50<Nmax<1.75;
• and
• −0.5<f4/R6<2.0.