of the biaxial crystal by utilizing internal conic refraction an optical low pass filter that can achieve the two dimensional false color reduction effect is realized by the simplest structure in the form of one crystal plate since the optical low pass filter according to this embodiment is composed of a single crystal plate it can be produced more easily as compared to conventional optical low pass filters having a complex structure that needs a plurality of crystal plates such as a birefringent plate and a phase plate which require a long processing time in the case where a plurality of crystal plates are used they frequently become defective due to dusts scratches and defects produced in the process of polishing cutting matching coating and bonding in contrast the optical low pass filter according to this embodiment suffers from less dusts scratches and defects since it is composed of a single crystal plate therefore an excellent optical low pass filter can be obtained easily the crystal used in the optical low pass filter according to this embodiment is not limited to mg 2 sio 4 forsterite but other transparent biaxial crystals belonging to the orthorhombic system the monoclinic system or the triclinic system can also achieve similar effects for example tridymite sio 2 mica kal 2 alsi 3 o 10 oh 2 chrysoberyl beal 2 o 4 aragonite cao co 3 fluorine type topaz al 2 sio 4 f 2 and gypsum caso 4 2h 2 o may also be used in the case where the optical low pass filter is used in a digital camera it is advantageous in saving space and enhancing.