by Henry Koren, inspired by Paul Romanczyk, edited by Norman Koren
Not all MTF measurement systems will necessarily provide the same results. The quality of the test target can impact the measurements you obtain. Long distance tests are ideally performed at the hyperfocal distance, where there is enough depth of field to have acceptable focus at infinity. Long-range tests which exceed the available space within your lab or factory are the most challenging. A collimator or relay lens system can be used to produce virtual targets at a simulated distance. The measurements obtained through a collimator can diverge from measurements obtained from free-space test targets. This article will discuss how to cope with that.