TIRPOR - The Irrational Pursuit Of Reason





This page contains an interactive calculator for depth of field, effective aperture and suggested slice depth when stacking images.

The calculator is biased towards my equipment- if you have specific lenses, CoC values, apertures, etc you want adding just let me know.

You can get bogged down in theory - s the way I work is to use these values as a starting point and then check what happens in practise.

Simple symmetric lens

First for a typical use of a reversed enlarger lens on a bellows, modelled as a symmetric lens, to give around 1 to 5x optical magnification we have:

Parameters Equations
F = lens aperture Magnification =(Si-f)/f
c = circle of confusion Effective aperture = F * (1+m)
m = magnification Symmetrical DOF = 2Fc((m+1)/(m^2)
f = lens focal length  
Si = Image distance (sensor plane to lens plane)  
User parameters> Calculated values
Circle of Confusion Optical Magnification
Lens focal length Effective aperture
Sensor to lens (Si) Depth of Field
Lens aperture Recommended slice (70%)
Working distance for a reversed El-Nikkor 50mm f2.8N, Newtonian model, reversed planes. Other lenses may not work.

Microscope objectives

The next case is for using microscope objectives. The ones I have available are for finite tube length Nikon ELWD and SLWD PLAN versions. the Depth of field formula is a bit different this time and takes into account the refractive index of the medium in which the sample is immersed and the wavelength we are using. I only use air (you can increase DoF by using oil or high refractive index liquids) and usually consider 550nm (or 0.55 microns) as an appropriate wavelength.

Parameters Equations
l = wavelength F = 1/(2NA)
c = circle of confusion Effective aperture = F * (1+m)
m = magnification DOF = (ln/NA^2) + c(n/mNA))
NA = objective numerical aperture  
F = lens aperture  
n= refractive index  
User parameters> Calculated values
Circle of Confusion Magnification
Objective magnification Effective aperture
NA Depth of Field
Recommended slice (70%)

El_Nikkor 50mm f2.8N Enlarger lens reversed on bellows - terminology

El-Nikkor 50mm f2.8N reversed