it is all mathematics. There is probably a calculator available that can do this.
The issue is that not all crop sensors are the same. Some are 1.4. 1.5 or 1.6 crops, and then you have the 4/3rd system and now micro 4/3rds. This is without considering the compacts and their sensors. Any calculation needs to be based on the crop factor of any particular cameras sensor.
"It is one thing to make a picture of what a person looks like, it is another thing to make a portrait of who they are" - Paul Caponigro
Constructive Critique of my photographs is always appreciated
Nikon, etc!
RICK
My Photography
If you have a look at this on line depth of field calculator you can enter differing camera ( FX or Dx ) formats, makes and models to show you the resulting depth of field at varying apertures.
Just read an article that clears this up. 1.5crop at 3.5 is same as FX at 5.6!
That's just crazy, now I know why some insist on FX, hmm.