focal length, fresnel, objective (beginner stuff)

[ppmz]

Hi All,

This is a real newbie question, but it's hard to know what keyword to search for to find this answer.

I have the following items:

TFT: 15" (381mm)
Fresnel: Focal length 220mm/317mm
Objective: Focal length 320mm

An externally hosted image should be here but it was not working when we last tested it.

Is my diagram correct? Is there more to be considered? Does the objective's focal only determin the image size, and nothing else?

I suppose the TFT size doesn't matter, as long as the fresnel covers it?

Thanks.