Fixing device, image forming apparatus, and fixing method

A fixing device comprising:

• a fixing rotary body rotatable in a predetermined direction of rotation;
• a heater disposed opposite and heating the fixing rotary body;
• an opposed body contacting the fixing rotary body with releasable pressure therebetween to form a fixing nip therebetween through which a recording medium is conveyed;
• a heat shield interposed between the heater and the fixing rotary body and movable in a circumferential direction of the fixing rotary body to shield the fixing rotary body from the heater in a variable circumferential direct heating span of the fixing rotary body where the heater is disposed opposite the fixing rotary body directly;
• and
• a controller operatively connected to the heater and the heat shield to move the heat shield after the controller turns on the heater as a print job starts so as to change an area of the direct heating span of the fixing rotary body.