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Frequently asked Questions (FAQ)

Answers to frequently asked questions. If you have a question not answered here, send an email to

I have entered a tilt value on a specific surface but I do not see any effect in the lens layout plot.
You must activate tilted and decentered surfaces in the ray trace by specifying "D" in the surface type. In the command line, type "SUT s3 SD" (without the quotes), where "SD" means that the surface (3) is spherical and decentered. Alternatively, in the surface spreadsheet editor, simply add "D" to the existing surface type qualifiers. Similarily, for a decentered aspherical surface, enter "AD" (A = aspherical, D = decentered/tilted).
This method also allows deactivating surface decenter/tilts by simply removing the "D" qualifier.

Rays are not blocked on a surface with central obscuration.
Rays are only checked, whether they are inside or outside a surface aperture, if height checking is activated. For example, to activate height checking on surface 3, type in the command line "FHT s3 1" or, in the surface editor, enter 1 into the "*" column on the appropriate surface in the surface editor.

I always get 100% transmission irrespective of the optical system in use.
Transmission analysis is controlled by two settings. To take reflection losses at optical interfaces into account, use the ''POL yes'' command prior to transmission analysis. Transmission losses due to absorption in bulk material are included with the ''TRA yes'' command. Both settings can also be conveniently controlled via the configuration dialog, which is accessed from the main menu Edit/Configuration data. Check ''Include Transmission'' and/or ''Include Polarization'' in the ''General'' tab.

How does a user scroll the Text Window lines from the keyboard?
The PgUp and PgDn keys scroll entire pages whereas the arrow-up and arrow-down keys scroll lines. Make sure that the Text window has focus (i.e. click on it before scrolling). Likewise, if the command line has focus, the up/down arrow keys invoke the history of commands entered.

Rays in the Lens Layout Plot do not change after modification of system parameters, e.g. field or aperture settings.
Open the option dialog of the lens layout window and check "Auto-update rays". Then rays are permanently updated when a new lens layout is drawn.

Optimization stopped with error message "Probable cause in targets/constraints definitions", for example at SPD f1 = 0
This is an error function definition that will most likely not work because in almost all cases it is impossible to have the spot diameter (SPD) EXACTLY zero. So, the program tries to do something impossible and recognizes this. Therefore the warning message. A better optimization function would be "SPD f1 0", that is omitting the equal sign "=". Then, aberrations are minimized instead of exactly solved.

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