What is the best method for photographing diamonds and jewelry (such as 18k diamond rings) (that is, the sparkling effect of diamonds and the luster of metal can be very good)

This is not a camera problem, it’s that you don’t know how to take pictures of jewelry and you don’t know how to use up the light. Photography is called "light painting" in Japanese, which can be vividly explained as painting with light. Therefore, to make diamonds shine, you must use high-brightness spotlights and adjust the lighting angle and distance appropriately to allow the light to refract into the lens. The background can be made of black gold velvet to avoid stray light interference and highlight the subject. It is best to use a tripod to secure your camera. The sensitivity does not need to be too high, otherwise noise will affect the image quality. Set aperture priority mode and shoot with different apertures, which will have different depth of field effects. Use spot metering mode, or reduce the exposure compensation by about 2 stops. Try it a few times and you will get satisfactory results. I wish you good luck.