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© Rodenstock GmbH
Status: September 2023
6.2 Measurement accuracy
Technische Messgenauigkeit:
• Resolution in x- and y-direction: 0.11 mm (in measuring distance 600 mm to mirror)
• Resolution in z-direction: 0.16 mm
6.3 Repeatability (standard deviation with repositioning of the customer)
The following values are results from numerous test series with the ImpressionIST® measuring devices. In these,
the accuracy of the 3D measurement system was verified and studies on habitual head and body posture as well
as on convergence behavior were conducted.
Pupillary distance < ± 0.2 mm
Cornea vertex distance: < ± 0.6 mm
Face forme angle: < ± 0.6 °
Pantoscopic tilt: < ± 1.5 °
Lens length: < ± 0.2 mm
Lens height: < ± 0.2 mm
Distance between lenses: < ± 0.2 mm
6.4 Measurement procedure
On the following pages you will find detailed information on all measurement methods used by the
ImpressionIST® 4+.
6.4.1 Measuring principle
Recording your customer with the two integrated cameras enables precise 3D measurement of the individual
parameters: Camera 1 is placed on the right in the center of the camera slide, camera 2 is integrated in the lower
left corner in the camera slide.
▪ The principle:
Since both cameras are triggered at the same time, two images of the customer are created
simultaneously. The image from camera 1 shows the customer laterally from the left and camera 2
shows him diagonally from the bottom right. These synchronous images are the basis of our patented
stereo measurement principle.
• Habitual head and body posture
The barely visible cameras record the customer with his frame while he stands in front of the mirror in a
situation he is used to.
▪ The benefit:
Your customer adopts an unconstrained habitual head and body posture, which means that the
measurement is performed in a posture that is habitual for your customer and appropriate for the case of
use, further increasing the accuracy of the measurement. Nevertheless, as with all centering devices, it
is important that you observe the client's head and body posture. If necessary, ask him to walk a few
steps and stand in front of the device again.
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