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.

I think,

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



1 Answer 1


The DoF calculators won't work well here, unless they are specifically designed to handle these extremely short distances.

To calculate DoF for macro distances you can use magnification-based formula

DOF = 2*N*c*((m/P+1)/m*m)

Where N is f-number, c is circle of confusion (typically 0.025 mm or 0.001 in), m is magnification and P is pupil magnification. f-number you know, circle of confusion is above, magnification you can figure out. The problem is the P - pupil magnification. For symmetric lenses it should be 1, but your lens is most likely a telephoto construction, for which P should be less than 1, possibly 0.5. I am not sure if you can figure out P for your lens exactly.

There is a detailed article Depth of Field on Wikipedia.

It is a good idea to consider these DoF calculations only as a starting point, because there are many factors like lens construction, size of the print etc. that play important role in the final perception.


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