What MTF50 is Needed for Prints?
Determining MTF50 depends on the print size. If you plan to print large posters (20 × 30 inches or over), the more MTF50, the sharper your prints will appear. Any high-quality, 4+ megapixel digital camera (that is, one that produces good test results; MTF50(corr) > 0.3 cycles/pixel) is capable of producing excellent 8.5 × 11 inches (letter-size; A4) prints. At that size a fine DSLR wouldn’t offer a large advantage in MTF. With fine lenses and careful technique (a different RAW converter from Canon’s and a little extra sharpening), my 6.3-megapixel Canon EOS-10D (corrected MTF50 = 1340 LW/PH) makes very good 12 × 18-inch prints (excellent if you don’t view them too closely). Prints are sharp from normal viewing distances, but pixels are visible under a magnifier or loupe; the prints are not as sharp as the Epson 2200 printer is capable of producing. Softness or pixilation would be visible on 16 × 24-inch enlargements. The EOS-20D has a slight edge at 12> x 18 inches; it’s about as sharp as I could ask for. There’s little reason go to a 12+ megapixel camera likie the EOS 5D, unless you plan to print larger. Sharpness comparisons contains tables, derived from images downloaded from two well-known websites, that compare a number of digital cameras. Several outperform the 10D.
The table below is an approximate guide to quality requirements. The equation for the left column is
\(\mathit{MTF50}(\text{
Table 1. Print quality requirements.
|
Requirement (MTF50 in line widths ⁄ |
Quality Level |
|---|---|
|
150 |
Excellent (extremely sharp at any viewing distance, about as sharp as most inkjet printers can print) |
|
110 |
Very good (large prints [A3 or 13 × 19 inches] look excellent, though they won’t look perfect under a magnifier; small prints still look very good) |
|
80 |
Good (large prints look OK when viewed from “normal” distances, but somewhat soft when examined closely; small prints look soft, which is adequate, perhaps, for the “average” consumer, but definitely not “crisp”) |
Example of Using the Table
My Canon EOS-10D has MTF50 = 1335 LW/PH (corrected; with standardized sharpening). When I make a 12.3-inch high print on 13 × 19-inch paper, MTF50 is 1335/12.3 = 108 LW/in: “very good” quality; fine for a print that size. Prints look excellent at normal viewing distances for a print this size.
This approach is more accurate than tables based on pixel count (PPI) alone (though less refined than SQF, below). Pixel count is scaled differently; the numbers are around double the MTF50 numbers. The EOS-10D has 2048/12.3 = 167 pixels per inch (PPI) at this magnification. This table is not definitive; it was first published in October 2004, but may be adjusted in the future.