Spreadsheets to help the focussing process

Part of largeformatphotography.info.

An spreadsheet for determining plane of focus and depth of field using Merklinger's method

by Eirik Berger © 2002

I made a spreadsheet (Excel) which helps you to determine the plane of sharp focus. It also gives you information about areas where you have acceptable sharpness at different apertures. This table is a perfect tool in the field, print one table for each lens. You need to input:

The spreadsheet gives yo the plane of sharp focus at different lengths (A) between lens and film. The little table at the bottom tells you in what area you have acceptable focus. The "math" is based on the content of Merklinger's articles "The Scheimpflug rule" part 1-4 and "Depth of field for view cameras" part 1-2.

Here is an example: the focal length is 90mm, and the distance (J) from the lens to the "hinge line" where the plane of sharp focus meets the "parallel to film" (PTF) plane is set to 175 cm. And then we want the angle of the plane of sharp focus to be 60 degrees (0 degrees is upwards along the film plane). The tilt-angle of the lens is 2,9 degrees (or 3 to make it simple) Then we can read out of the table that the lens to film distance (A) must be 93 mm. The plane of sharp focus will "rotate" around the hinge line beneath the lens. Then we decide to use aperture f64, in the lower table we see that g=3,84mm (or 4mm to make it simple). Then you count 4 mm up and down from 93 mm and determine the near limit and far limit of the zone of acceptable focus. At aperture 64 the zone of acceptable focus is between 36 and 104 degrees. If you use a different aperture the outer limits of the zone will change accordingly.

Download the Excel file

Spreadsheats to estimate on-film resolving power

by Frank Loeffel © 2003

These spreadsheets try to estimate on-film resolving power based on defocus, film resolution and lens resolution. The premise is that final resolution is more interesting when focusing than resolution solely based on a circle of confusion.

There are two versions. One is for large format work, where defocus can be determined by the displacement at the ground glass. The other one is for medium (and small) format work, where defocus can be determined by displacement at the lenses' DOF scale.

Download LF Excel file

Download MF Excel file