How to set the lens mount reference for thermal analysis

OpticStudio can model the thermal variation of an optical system. This article shows the default mechanical reference that OpticStudio uses for the lens mount and how this can be changed in Sequential Mode.

Authored By Nam-Hyong Kim


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In Sequential Mode, the Make Thermal tool allows to model a system in multiple environments with different temperatures. It can be used in conjunction with dummy surfaces to show how a system changes when undergoing thermal variation. This article provides a brief overview of how to set up the dummy surfaces to represent a lens mount, and then how to observe multiple configurations of the system with the Make Thermal tool. 

Default mechanical reference of the lens mount  

By default, the lens mount is assumed to contact the lenses as shown below. The rear surface of the front lens and the front surface of the rear lens physically contact the mount (shaded in green).

lens mount

The animation below shows how the optics and mount expand and contract with temperature.

3d layout

Changing the mechanical reference of the lens mount

Sometimes, the mechnical reference (contact point) between the mount and lens needs to be different. For example, having the mount contact the right surface of the right lens in the layout above. This can be achieved by using extra dummy surfaces.

extra dummy surfaces

Example showing the thermal variation

Let's modify a system to make the mount contact the rear-surface of the right lens. Open the attached sample file "rear_mount_sample_1.zar". Modify the Lens data Editor as following.

modify lens data editor

This system models nominal center air gap of 100mm. Notice how the spacer (surface #2) goes all the way to the back of the lens, by its thickness being 140 instead of 100. The dummy propagation on surface #3 needs to be same as the thickness of surface #4 at any temperature; therefore, the TCE of surface #3 has to be the same as the TCE of N-BK7 glass. The TCE of the glass is specified in the glass catalog, and for N-BK7 it is 7.1. Enter this value in the TCE column of surface #3 in the LDE.

modify lens data editor 2nd

Using the Make Thermal tool, create multiple configurations at different temperatures. If the temperature of one of the configurations is sufficiently different than the nominal, the 3D layout will look like the following: 

3d layout



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