How to test Lens - testing and resources
How to Test Your Lens
High Resolution Test Patterns
Norman Koren photography
The test charts come in several flavors, identified by their intended length when reproduced on film or a digital sensor, gamma, length in pixels, and ink spread correction. Similar test charts, with the sacle omitted, can be created using Imatest Test Charts.
Chart length: The names of the charts below (2.5 and 5mm) are the intended lengths of the chart when reproduced on film or a digital sensor. They are designed to be printed at 50, 80, or 100x magnification (relative to the intended size on the film or sensor) to avoid printer limitations.
2.5 mm charts (illustrated above) are designed to be printed 25 cm (9.84 inches) long (100x magnification) on a 4.5x11 inch strip— half of a letter sized or A4 sheet. The 7086 pixel long charts are best for printing at multiples of 720 dpi (Epson printers). The 5906 pixel long charts are best for printing at multiples of 600 dpi (Canon and HP printers). 2.5 mm charts are recommended for compact digital cameras, which have tiny sensors (11 mm diagonal or less) and lenses with relatively short focal length.5 mm charts are designed to be printed 25 cm (9.84 inches) long (50x magnification), which fits on a 4.25x11 inch strip— half of a letter sized or A4 sheet, or 40 cm (15.75 inches) long (80x magnification), which fits on half of an A3 sheet.You can print these charts any size you want as long as you note the magnification and photograph them at the appropriate distance, but I recommend the standard sizes to avoid confusion.
Print magnification: advantages/disadvantages
- On the Epson 1270 or 2200 with semigloss paper at 1440 dpi, the high spatial frequency bars are clearest when printed at the highest magnifications. At 100x, bars are clear with no tonal shift up to 200 lp/mm. At 80x, some tonal shift due to ink spreading is noticeable starting at 170 lp/mm, but the bars are still distinct at 200 lp/mm. At 50x, tonal shift starts around 120 lp/mm. Bars are still distinct at 200 lp/mm, but MTF is slightly reduced. Realistically speaking, 50x is adequate for film and digital SLRs; there is little real action above 100 lp/mm. But since "resolutions" as high as 150 lp/mm have occasionally been published, many of you (myself included) may be curious about what you can see over 100 lp/mm. A portion of a 400 dpi Epson 1640SU scan of a 50x chart printed on the Epson 1270 at 1440 dpi, between 80 and 200 lp/mm (gamma = 1.5), is shown below. This is the worst case, and it looks pretty good. I strongly recommend that you examine your printed charts under a loupe (at least 10x) to be sure the bar and sine patterns look good at high spatial frequencies.
The Imaging Resource Test Suite More than you probably wanted to know about testing digital cameras
Testing and Targets
Lens test image quality