The resolution of a lens is limited by diffraction and calculated using the effective F-number K’. The best possible resolution is achieved by closing the lens aperture by 1 to 2 steps, so that the lens resolution approaches the diffraction limit. Adjacent image elements become distinguishable when their distance is:
With a optical wavelength λ for visible radiation of 550 nm this leads to e.g.:
| Effective F-number K’ | Diffraction limit Resolution* ∆y’min [μm] |
|---|---|
| 2 | 2.6 |
| 2.8 | 3.7 |
| 4 | 5.3 |
| 5.6 | 7.4 |
| 8 | 10.8 |
| 11 | 14.5 |
| 16 | 21.1 |
| 22 | 29 |
| *at wavelength λ= 550 nm | |
Effective F-number K’ = 8
Wavelength λ = 550 nm
Diffraction Limit ∆y’min = 10.6 μm
Schematic depiction of the imaging system and definition of variables used.
f = Lens focal length (mm)
S = Sensor length (mm)
L = Length of Region of Interest (ROI) of object (mm)
a = Object range (mm)
a’ = Image distance: Distance from sensor to HH’ (mm)
β = Magnification
w = Field angle
OO’ = Distance from sensor to measured zone (mm)
s’A = Flange focal length (mm)
∆s’ = Lens extension (mm)
LT = Tube length
A = Working distance (mm)
HH’ = Principal point distance (mm) (can lengthen or shorten OO’)
s’K = Camera flange length consisting of focus adapter series FA22 and extension rings series ZR (mm)
LO = Lens length (mm)
