affect the imaging quality

magnet bullet: also called the photoelastic effect or photo elastic effect. The transparent medium some isotropic, nature has birefringencewith mechanical stress, which is also called mechanical birefringence, stress birefringence or optical effect etc.. The effective stress in the direction of the optical axis, proportional to the stress birefringence and causes.Photoelastic effect for optical processing a lot of trouble, neodymium block magnets glass annealing is insufficient or not installed good will produce stress in the glass, resulting indouble refraction