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

<!-- Begin
function doField(form) {
distance = (form.distance.value)*1000;
CoC = (document.form.format.options[document.form.format.selectedIndex].value);
aperture = (document.form.aperture.options[document.form.aperture.selectedIndex].value);
focal = form.focal.value;
if (isNaN(distance))  {
alert('Please enter a numerical value for subject distance.');
document.form.distance.focus();
document.form.distance.select();
}
else {
if (isNaN(focal)) {
alert('Please enter a numerical value for focal length.');
document.form.focal.focus();
document.form.focal.select();
}
else {
hyperfocal = (focal * focal) / (aperture * CoC);
dofNear = (hyperfocal * distance) / (hyperfocal + (distance - focal));
form.dofNear.value = Math.round(dofNear) / 1000 + " m";
dofFar = (hyperfocal * distance) / (hyperfocal - (distance - focal));
if (dofFar < 0) {
form.dofFar.value  = "\u221E (infinity)";
}
else {
form.dofFar.value  = Math.round(dofFar)/1000 + " m";
}
dofTotal = Math.round(dofFar - dofNear);
if (dofTotal < 0) {
form.dofTotal.value  = "\u221E (infinite)";
}
else {
if (dofTotal >= 0 && dofTotal < 0.001) {
form.dofTotal.value  = "<1 mm ";  
}
else {
form.dofTotal.value = dofTotal / 1000 + " m";  
         }
      }
   }
}
}
//  End -->