The September 19, 2005 release of ZEMAX deleted an obsolete control: the  "Use Temperature, Pressure" checkbox on the Environment Tab of the General Data dialog. When this box was checked, ZEMAX adjusted the index data to the current environment. Since this adjustment is always correct based upon the documented way of defining dispersion data, the checkbox is considered obsolete and was removed in the September release.

Unfortunately, we became aware that at least one user had incorrectly defined the reference temperature of some custom glass data, and this change therefore altered the incorrect index data in an unexpected way. This problem will only occur if

a) The "Use Temperature, Pressure" checkbox was off,

b) User defined dispersion data had been added that was referenced to air at 20 degrees C and 1.0 ATM (which ZEMAX uses as the reference if the checkbox is off), and

c) The user defined dispersion data incorrectly defined the glass reference temperature as the actual working temperature of the glass rather than the temperature to which the index data was referenced, which must be 20°  if the checkbox is off.

In summary, if ZEMAX's own thermal adjustments were disabled, and if the reference temperature of any custom glass data was not 20 degrees, then the September 19 release will return index data different than earlier versions of ZEMAX. To maintain back compatibility with these incorrectly set up files, the checkbox has been reinstated and renamed “Adjust Index Data To Enviornment”.

It is recommended that this switch always be checked ON.

Warning messages will now be issued if this feature is checked OFF and the glass reference temperature does not match the surface temperature.It is strongly recommended that any such warning message be addressed and resolved.