Nikon will never reveal their real designs, but instead patents facsimiles of them.  Try patent searches, that's about as close as you're going to get.

Hi Marzanna,

What is the lens you are trying to simulate? Patent search is one way as @Mike.Jones pointed out, but a first approximation is to simply use a paraxial lens. It can already get you a long way.

One thing to note is that Nikon is generally using a 200-mm tube lens focal length. The magnification is the ratio between the tube lens and objective lens focal length. So, if your objective is 10X (in air), its focal length is 200 / 10 = 20.0 mm. You could use a Paraxial surface with a focal length of 20.0 mm to simulate the objective at first.

If you use an immersion lens, you may want to look into this custom surface by @Jeff.Wilde:

I also attempted to make a similar model based on a paper, but couldn’t reproduce the results of said paper:

So, it isn’t conclusive yet. I hope this helps.

Take care,

David

Hi,

Thank you for your answers. The objective I am using is 

with two Thorlabs lenses that make a telecentric setup

Best,

Marzanna