TIRPOR - The Irrational Pursuit Of Reason

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Introduction

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