Method Note 1

Resolution tests were run at a working distance of 7.7 meters. 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 balanced Wimberley head mounted on a Gitzo 1548 tripod. The head was locked and weighted with a large bean bag to dampen vibration. Two exposures at 1/250th second were taken at each aperture with an EOS-1n 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. After several tests, it was determined that camera autofocus function yielded consistently higher lpm 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.

Measurement were made at the center pattern, a middle pattern, and the far upper right pattern on the two exposures. The highest resolution score for each aperture was recorded to minimize the the effect of potential autofocus error (The standard deviation in autofocus tests with the EF 300mm f/2.8 lens was calculated as 5.9% [4.96 lpm]). Center-weighted resolution was calculated (60% center; 30% middle; 10% edge). Resolutions (lpm) at each f/stop were calculated using the method on the chart as follows.

Image lines per mm (image lpm) = 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