# Tube Length

## Tube Length

Tube Length LT = flange focal length + lens extension (Camera flange length)

{!{!{LT=s'A_∞+∆s'-s'K}!}!}

### Example

Rodagon 4.0/80

Focal length      f = 81 mm

Magnification              β = 1/6

Flange focal length s’A = 74.7 mm

Camera flange focal length s’K = 19.5 mm

Lens extension   ∆s’ = f β = 81 mm/ 6 = 13.5 mm

Tube length   LT = 74.7 mm + 13.5 mm - 19.5 mm = 68.7 mm

The calculated tube length LT can be achieved by using e.g.:

+ focus adapter extension    6.7 mm

+ 2x extension rings ZR20    40.0 mm

Total     = 68.7 mm

Lens parameters scheme

### Imaging Parameters

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)