I am using Nikkor 105mm f/2.8G and its close focus is: 1 foot (0.314m, 31.4 cm). And depth of field for this distance is about 0.5cm (I have an application on my Android phone). How will change depth of field (close focus will be reduced, I think), if I add extension tubes , for example, 12mm, 20mm, 36mm. How can I calculate it fast? Have anyone know a program that can do it or better does anyone know the fast method how to calculate this.
1) Should calculate the new close focus distance
2) Should calculate new focal length of this construction
3) Should use DoF calculator for by typing focal length and focused distance to get DoF