Method for Resolution Measurement on Film

Resolution tests were run at varying distances from the target. An Edmund Scientific lens resolution chart was illuminated with a monolight flash adjusted with a flash meter at each aperture exposure. The lenses were mounted on a Bogen 3033/Arca Swiss B1 tripod/head combination with a large Kirk bean bag weighing down the tripod/head to dampen vibration. Three exposures at 1/250th second were taken at each aperture with an EOS-1v via cable shutter release on Kodak Technical Pan film rated at ISO 25 and developed in Technidol. The central autofocus point was centered over the center pattern for each exposure. No focus bracketing was used. In previous tests, it was determined that camera autofocus function yielded consistently higher line pairs per mm scores than trying to use manual focus and bracketing with an eyepiece magnifier. The lens was manually defocused, and then refocused using autofocus for each exposure. Line patterns were read under a compound brightfield microscope at a magnification of 40X.

Measurements were made for the following lenses:

• EF 70-300mm f/4.5-5.6 DO IS USM
• EF 75-300mm f/4-5.6 III USM
• EF 100-400mm f/4.5-5.6 L IS USM
• EF 70-200mm f/2.8 L IS with EF 1.4X extender (280mm)

Other lens resolution data was used for charts based on previous tests. See the index page to link to specific lenses.

Measurement were made at the center pattern, a middle pattern, and the far upper right pattern on the three exposures. The highest resolution score for each aperture from the three exposures were used to graph the data. Center-weighted resolution was calculated (60% center; 30% middle; 10% edge). Resolutions at each f/stop were calculated using the method on the chart as follows.

Image lines pairs per mm (image lpm or lp/mm) = lpm resolved on chart X (D-fo) / fo) where fo = focal length of lens and D = Distance from the chart to the middle of the lens.

Edmund Scientific Lens Resolution Chart	Detail of USAF 1951 test pattern