Method Note 1

Resolution tests were run at 87 inches 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. Four 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.

Measurement were made at the center pattern, a middle pattern, and the far upper right pattern on the four exposures. The highest resolution score for each aperture was recorded for data in the center-weighted resolution graph. Center-weighted resolution was calculated (60% center; 30% middle; 10% edge). For the graph displaying central point resolution, the means and standard errors based on all four exposures were calculated. 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.

Resolution performance data was run on 4 samples of the EF 85mm f/1.2 L and 1 sample of the EF 85mm 1.8 lens and one EF 85mm f/1.2L II. Three of the 1.2 L lenses gave similar results to data shown in both the first and second edition of the review. One refurbished lens had defective resolution performance and was returned to the seller. No data is shown from that defective/damaged lens.

Edmund Scientific Lens Resolution Chart

Detail of USAF 1951 test pattern