Hi @Yadong.Wang,

I don’t manage to give you a full answer. But, the reason your STOP has a fixed value is because you are using an aperture type: Float By Stop Size in the System Explorer. That means the aperture stop of your system is directly controlled by the Clear Semi-Diameter of the STOP. In the video that you linked, we don’t see the System Explorer, so I can only guess what aperture type Mark used. It’s definitely not Float By Stop Size, otherwise you’d have the same issue, and during the optimization, the entrance pupil diameter (ENPD) in the blue ribbon at the bottom of the screen changes quite dramatically (from 87.5243 to 388.047), so not Entrance Pupil Diameter. I wouldn’t use Image Space F/# because Mark seems to control the exit pupil with his REAY operands. That leaves us with Object Space NA, Paraxial Working F/#, or Object Cone Angle. And at this point, it would be best to ask the man himself. @Mark.Nicholson would you please do us the favor?

Take care,

David

Just saw this…let me have a look and I’ll reply fully