Hi Mona,

I think the easiest is to use a Analyze..Universal Plot..1-D..New.., this allows you to plot the value of a Merit Function operand against a parameter selected from a list.

You can set Independant Variable X as being the thickness of a dummy surface just before the focal plane, and have its value vary around zero, for example +/- 1 mm. You can also specify the number of steps you want to have.

Then, you can set Dependent Variable Y as the operand MTFA (I let you read the Help File about this operand and how to set it up), and you should be good to go :)

Below is the same plot from an example with the Double-Gauss sample file (attached to this post):

I hope this help.

Take care,

David