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Image Engineering
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3.4 Using the included 4-prong alignment aid
The 4-prong alignment aid can be used to set up the DUT (Device Under Test) at the optimal
depth inside the diffuser to ensure uniformity of above 90% for your measurements. Steps 1 - 5
(
) illustrate the process and how to position the DUT. The camera in this example uses
a circular fisheye lens with an angle of view of 180°. The lens, not the CAL3-XL creates the
visible keyhole effect.
Step 1
Step 2
Step 3
Step 4
Step 5
Figure 5: Using the 4-prong alignment aid
Image 1 shows the removable alignment aid mounted on the CAL3-XL
from the DUT’s point of
view. Images 2 through 5 show the DUT moving closer to the optimal depth inside the diffuser.
In image 5 you can see, illustrated by the red dotted lines, that the correct depth is reached as
soon as the four prongs have completely left the frame captured by the DUT. This process
works both for circular and non-circular fisheye lenses and it does not depend on the angle of
view of the DUT. What does, however, depend on the angle of view is the necessary depth
inside the diffuser to fulfill these criteria. Devices with an angle of view smaller than 180° do not
need to be positioned as deep inside the diffusor as devices with an angle of view of 180°.
In case your DUT uses a non-circular fisheye lens that reaches its maximum angle of view
diagonally, it becomes necessary to rotate the device around its optical axis so that the four
prongs are as close to the edges of the frame as possible.
3.5 Measurement precautions
Ensure the device under test is completely encased in a black housing with only the lens
uncovered. If it is not, we advice covering it with a black, non-reflective fabric such as Molton.
Covering the DUT will ensure that light from the CAL3-XL will not reflect off the DUT (especially
colored devices) and back onto the diffuser and distort the test results.
