telecentic + afocal = ??

[James S]

I've been working up a telecentric scan lens, but when I try to use telecentric aiming in combination with afocal mode I get extremely peculiar ray traces. The central reference ray is bent at the last surface so that it is parallel to the optical axis.  This is completely non-physical behavior, and goes away if I switch back to focal mode.  Any thoughts what could be causing this or how to solve it?  Any help would be very much appreciated.

Thanks,

  James

[DC Howards]

Afocal means the image (and object) are at infinity.

Telecentric implies that the exit (or entrance) pupil is at infinity.

Optically, you can't have both, which is likely the issue with the software. 

--
You received this message because you are subscribed to the Google Groups "OSLO-Talk" group.
To unsubscribe from this group and stop receiving emails from it, send an email to oslo-talk+...@googlegroups.com.
To post to this group, send email to oslo...@googlegroups.com.
Visit this group at http://groups.google.com/group/oslo-talk.
For more options, visit https://groups.google.com/groups/opt_out.

[James S]

Hi Joe,

Thanks for the idea, but I'm not entirely convinced this is the issue.  OSLO's "afocal mode" doesn't appear to actually require that the lens be "afocal."  So far as I can tell, it just means that image space rays are reported in angular units, which is exactly what I want.  Here is the paragraph from the manual:

-------

Afocal mode
An afocal system is one in which the principal points and focal points are at infinity. This does not
necessarily imply that the object and image are at infinity. However, in the case where the image
is at infinity, special procedures must be used in ray tracing because image-space rays can not
actually be traced to infinity. The term afocal on the image side is sometimes used to describe the
situation where the image is at infinity, whether or not the actual system is afocal.

OSLO has an evaluation mode called afo that causes image-space ray displacements to be reported
in angular measure, optical path differences to be referred to a plane wave in the exit pupil of a
system, and field sags to be reported in diopters. Afocal mode has no effect on single ordinary
rays.

-------

I also found an "aberration mode" that can be set to transverse or angular, but this doesn't seem to affect how the spot size is reported.  I also considered just adding a perfect lens at the end of the system, the issue there is that it is rather tough to constrain the EFL of the part of the system that I actually care about.

Thanks,
  James