# Estimating the optical resolution of a lens

In Tony & Chelsea Northrup's recent video titled 5 Lies Camera Companies Tell You, they mention that the optical resolution of a kit lens is often lower than the resolution of the sensor at around 5 minutes in. Wikipedia has a section dedicated to measuring the optical resolution.

However, this is not comprehensive. Is there a relatively simple method of estimating the resolution of a lens? I don't have an actual use for this information, so if it's significantly easier to estimate rather than calculate, that is satisfactory too.

Some lenses - such as the Raspberry Pi lenses for the High Quality Camera - do quote a number for resolution, but none of the lenses on my system (Micro-Four Thirds) as far as I was able to find.

Norman Koren has a test chart for measuring MTF 10/MTF 50... you can also use the chart to visually estimate the MTF to w/in about 10% accuracy. But the results will be system MTF and not the MTF resolution of the lens alone.

• You should substantiate the 10% accuracy claim. That would place the human eye at about half as good as imatest. Usually in "man vs machine" for precise sensing, man loses. Jun 21, 2020 at 0:35
• @BrandonDube, I just restated what is in the article... although, I have used it myself and I got numbers reasonably close to Imatest results posted online (actually a little higher; but I was using a D850, evaluating the jpegs, and it's a best estimate). Jun 21, 2020 at 14:31

Each lens, as it comes off the assembly line is unique. In other words, each likely varies somewhat from the specifications of the design criteria. Now all lenses suffer from the twin demons of refection and interference. Both plagues, diffraction happens when light rays just graze the blades of iris diaphragm (aperture opening). These rays are not choked off, instead they are caused to alter their path and intermix (interference) with nearby rays that did not encounter an obstacle. The result is series of interference bands. The intensity of the bands decrease in intensity and spacing thus they trail off and become naught.

This phenomena effects every lens and was well studied by John Strutt, English Physicist, 1842-1919, Nobel Laureate, Physics, a nobleman, 3rd Baron Rayleigh. His published works on lens resolution is know as the Rayleigh Criterion (remains today as the basis of lens resolving power) "the revolving power of a lens will decrease as the diameter of the aperture increases (opens up)".

This will differ somewhat as to wave length. For pictorial devices, 589 millimicrons is often quoted.

f/1 = 1392 lines per millimeter f/1.4 = 557 lines per millimeter f/2 = 696 lines per millimeter f/2.8 = 497 lines per millimeter f/4 = 348 lines per millimeter f/5.6 = 249 lines per millimeter f/8 = 174 lines per millimeter f/11 = 127 lines per millimeter f/16 = 87 lines per millimeter

Note: These are the maximum possible resolving power. The resolving power for f/8 is higher than that of a pictorially useful film emulsion.

• Reflections cause ghosts, which do not reduce resolution. Manufacturing variation is orthogonal to OP's question. Jun 21, 2020 at 0:41