Hi David: 

-- First off thank you for all your time and effort to put together such a detailed example.   It will take me awhile to digest it, as i am not very familiar ZOS-API. 

 But from what you’ve outlined i think that if one wants to say drive axial color to zero across a limited range of surfaces (1-6), all I need to do is set the data field of UDOC11 to zero,  and sum across the range of surfaces (1-6) to define a new operator,  then use that constraint, with a target value of zero..  (I THINK ??)   I will test it out.   Once again,  thanks for your explanation and support on this. 

-- James..   

@James

As I mentioned, I’m not familiar with what it means to “achromatize” a single lens group in an assembly, so I’m not exactly sure what you want to get. I’ve just made the UDOC because I thought it would help you do what you want. You can even modify my code to have parameters for a start and stop surface, and have the code return the sum directly (I can help you with that if needed). Those UDOCs add quite a bit of overhead to the computation of the Merit Function, you kinda want to use as few as possible. If you give me more explanation about the “achromatization” process and what it means, perhaps I can come up with a better idea.

Take care,

David

@Andrey.Pravdivtsev 

Thanks for clarifying. So if I understand correctly, you want to optimize each group separately, and this should lead to a comparatively good overall design, is that right? What concerns me is: how do you know that the best lens assembly is a combination of all the best lens groups individually? Why can’t it be that the best overall zoom lens has one suboptimal lens group, for example? In other words, I don’t get why the lens group would be independant from one another. Does that make sense?

Take care,

David

If EFLY has a wavelength input, then you can use it to get the focal length of a range of surfaces at a given wavelength.  Use a few of those to build a constraint on the axial color of different lens groups.  

A couple reasons. First, you don’t want huge CA in one group that has to be canceled by another group. That will lead to tight tolerances on element power and Abbe.  Kind of like how you don’t want an element with large positive power that’s cancelled by one with large negative power. 
 

Second, I think it will optimize better.  The Zemax optimizer, especially the DLS, is weak and needs all the help it can get. 
 

Yes it will be tricky to figure out how low the CA in each group needs to be, without over constraining the overall design.  It will take some thought and maybe trial and error.  

Jeff, yes, and the optimizer won’t find those solutions on its own, so it needs constraints to pull it in the right direction.  

Several good references discuss the need to achromatize the individual groups in a zoom lens.

From Field Guide to Lens Design, by Bentley & Olson, p. 48:

 

From Introduction to Lens Design, by Sasian, p. 205:

 

From Handbook of Optical Systems Vol. 4, by Gross, p. 505:

It is interesting that the Seidel coefficients are calculated for the quite specific rays so if rays in your groups doesn’t satisfy these ray parameters these calculations looks quite useless.  Also the raypath will be different for different zoom positions.

HI ALL: 

-- I am still digesting all the great responses we got from this question that sparked a dialogue.   A big thank you to @Jeff.Wilde  and @PhotonHerder ,  who answered @David.Nguyen  more clearly than i probably could have.   So, yes i am trying to achromatize a  lens group/section, within a larger optical system,  as our veterans laid out.   
 

--  @Andrey.Pravdivtsev ,   I also liked your idea of  adding more zoom positions and “ignoring” surfaces outside the area of concern.   I am aware that ignore in available in the Non-sequential mode.   Is there also a way to achieve that in Sequential mode, when optimizing ? (EDIT-1:  I may have found MCE operands IGNR and IGNM for this ) 

(EDIT-2)

--  Another alternative, to evaluate a sub-group, while still using the the AXCL, LACL operands, is to create extra configurations, and using the GLSS (MCE-operand) and switch from the actual glasses in-use to air.  Thus, in-activating the surfaces not being evaluated.    

Again,  thanks to all who responded to my inquiry