Reinhard Schuster 
  
vertical goniometer (CVG). The test programs are run automatically and the results directly linked to the LH Systems 3. 
databases. 
3.2 CVG Hardware TI 
el 
The CVG was developed in 1998 by upgrading an existing vertical goniometer. Its main goal was the electronic testing 
of film-based analogue lenses under realistic operational conditions. Later, with the advent of digital cameras, hardware 
and software modifications were added to test the lenses together with the digital camera head (Pacey et al., 1999). 
  
Figure 9. Inserting optical systems into the CVG: 
a) objective UAGS for testing the optics b) engineering model of the ADS40 for calibration Un 
the 
Figure 9 shows the installation of test lenses into the CVG, whereby the lens entrance pupil must coincide with the pix 
swivel axis of the goniometer. Inside the swivel arm an auxiliary optics images a small code pattern to infinity. The len 
ADS40 lens under test refocuses the code pattern on to its digital sensors. Rotating the swivel performs a field scan 
along the CCD-line at nadir position. However, to address pixels outside the nadir line, a mirror scanner, moveable in Ow 
the x-direction, is mounted on top of the goniometer arm. From the contrast of the transferred image we deduce values the 
for the image quality; from the actual angles of swivel and x-scanner we gain the registration properties. the 
wit 
The code pattern consists of a series of stochastically arranged black and white bars of width 3 um pointing in two 
orthogonal directions. The code is designed to be sensitive to small lateral displacements to increase the accuracy for 3.5 
the registration measurement, and to possess sufficient spatial bandwidth for the image quality tests. 
The 
3.3 Measurement of the Image Quality unc 
eng 
As criteria for the image quality of a pixel the OTF (optical transfer function) across and along the CCD-lines is chosen. 
The OTF describes the complex variation of the transferred contrast through the optics with the spatial frequency. To 
ensure that the digital sensor lines are at best focus, the OTF must be measured at different depths of focus. This is 4 
easily accomplished by defocusing the small code pattern in the swivel arm. 
Phc 
Figure 10a shows the results of a measurement: The ideal code pattern (red) has contrast one, while the measured code pre 
signals (blue) show smaller contrast values. The OTF is mathematically deduced from both functions. Its amplitude the 
function MTF (modulation transfer function, upper curve in figure 10b, is already visible in the measured signals in the 
figure 10a, where code sequences with low frequencies exhibit a larger contrast than those with high frequencies. Note assi 
further that the OTF's phase function PTF (lower curve in figure 10b) is nearly zero over the full frequency range, thus the 
indicating a perfect, coma-free test lens. Again, this is nicely visualised in figure 10a, where the shape of all measured ordi 
code elements is highly symmetric. diff 
mul 
Int 
isn 
  
292 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B1. Amsterdam 2000.