// Javascript copyright Sean T. McHugh
//Cambridge in Colour Photography
// http://www.cambridgeincolour.com

<!-- Begin Required Focal Length Multiplier Calculator
function reqfoccalc(reqfocform) {
distance = reqfocform.distance.value;
dist_unit = reqfocform.unit1.value;
height = reqfocform.height.value;
height_unit = reqfocform.unit2.value;
sensorsize = reqfocform.sensorsize.value;
if (isNaN(distance)) {
alert('Please enter a numerical value for subject distance.');
document.reqfocform.distance.focus();
document.reqfocform.distance.select();
}
else {
if (isNaN(height)) {
alert('Please enter a numerical value for subject height.');
document.reqfocform.height.focus();
document.reqfocform.height.select();
}
else {
distance_m = distance/dist_unit; //distance to subject in meters
height_m = height/height_unit; //longest subject dimension in meters
sensor_m = sensorsize/1000; //longest sensor size dimension in meters
adjfocal = 1000*sensor_m * distance_m / (height_m + sensor_m); //focal length in mm
reqfocform.reqfocal.value = Math.round(10 * adjfocal) / 10 + " mm";
   }
}
}
//  End Focal Length Multiplier Calculator -->