A professional camera uses a better quality CMOS (complementary metal-oxide semiconductor) sensor, while a semi professional /entry level camera use CCD (Charge Coupled Device) sensor.

Thus the photo quality and the price of the two types of cameras vary drastically.

Working of a Digital camera

Light from the subject is focused using the optic lens to the sensor of the camera. The optic lens quality also depends on the image quality. The sensor will process the image and the light signal is converted to electric signal. Then the signal is magnetically stored in magnetic storage media like hard disks/flash memory.