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Moving lens thickness independently of other components

Question

I want to change the thickness/position of a group of surfaces (or a component group) without affecting the surfaces after the group. When I try to do adjust the first surface of the component group, all surfaces after that initial surface are affected. How do I restrict the thickness change so that it just affects the surfaces within the component group of interest?

Synopsis

Moving lens thickness independently of other components

Solution

For purposes of this discussion, let's assume that the lens or component you would like to re-position occupies surfaces 3 and 4 in your system. This corresponds to the surfaces of the negative lens in a standard triplet: There are 3 approaches outlined below that are easily implemented: The first approach involves making the surface directly following the group (surface 5) a global coordinate surface:
  1. Before you begin changing thicknesses, change surface 5 to a global coordinate surface by performing the steps:
    • In the "SPECIAL" column, choose "Coordinates(C)" from the pop-up list
    • Choose "Coodinates:" = "Global" from the resulting dialog window.
    • Accept the "global reference surface" as "1" in the pop-up window.
    • Accept the changes to the Coordinate Data window by closing it by clicking on the Green Check in the upper left cornerof the window. This effectively "locks" the position of surface 5 in place with respect to surface 1.
  2. Now you can go to the surface preceding your intended group (surface 2) and change the thickness as you wish. Only the surfaces in the intended group will be affected.
The second approach involves implementing a "minus thickness" pickup on the thickness of surface 4 which relates to the thickness of surface 2. The idea is that when the thickness of surface 2 is reduced, the thickness of surface 4 is increased by the same amount:
  1. Perform the following steps on surface 4:
    • In the "THICKNESS" column, choose "Pickups(P) >> Minus Thickness..." from the pop-up list
    • Choose "Enter pickup source surface" = 2 and
    • Choose "Enter pickup constant" = X. Where X is the addition of the current thicknesses of surfaces 2 and 4.
  2. Now change to the thickness of surface 2 to whatever you wish and the pickup on surface 4 will keep surfaces 5 and higher in the proper position.
This pickup will always set the thickness of surface 4 to be the value of X minus the thickness of surface 2. The third approach is similar to the last approach only you "minus length" pickup on the thickness of surface 4. The length pickup maintains the total length of a range of surfaces by continually adjusting one surface. The idea will be that the thickness of surface 4 will be adjusted so that the total length from surface 2 to 4 (inclusive) is maintained:
  1. Perform the following steps on surface 4:
    • In the "THICKNESS" column, choose "Pickups(P)>>Minus Length..." from the pop-up list
    • Choose "Enter pickup source surface" = 2,
    • Choose "Enter second pickup source surface" = 4 and
    • Choose "Enter pickup constant" = X. Where X is the total length from surface 2 through surface 4 inclusive (X = thickness of surface 2+3+4).
  2. Now change to the thickness of surface 2 to whatever you wish and the pickup on surface 4 will keep surfaces 5 and higher in the proper position.
This pickup will always set the total length of surfaces 2 through 4 to be the value of X minus the thickness of surface 2.