Grundig GCA-B1002B Owner's Manual page 6

4.3. Back Focus Adjustment
When to adjust the back focus:
Back Focus refers to the distance from the rear lens element to the camera focal plane.
It is only required to adjust the back focus only when the focus cannot be adjusted
throughout its zoom range.
Requirements:
Tools required when carrying out back focus adjustment include:
1. Test chart / contrasting object
2. Allen Key (depending on the camera model)
How to adjust the back focus:
Step 1: Set the camera on a stable mount, with the test chart or object at least 75 feet
(23 meters) away (or as far as possible). Please loosen the Back Focus Retaining Screw
by hand or with the supplied Allen Key (depending on the camera model).
Step 2: Make sure the iris is wide open. Therefore, it is advised to keep the environment
in low light condition. To open the automatic lens completely, please use a neutral
density filter. With this filter it is possible to simulate a low light condition so that the lens
can open up completely.
Step 3: Adjust the focus to infinite far (∞).
Step 4: Turn the zoom to the wide angle position, and then focus with the back focus
adjustment on the test chart.
Step 5: Set the zoom now to the most extreme telephoto position.
Step 6: Focus on the object with the focus screw of the lens (not with the back focus
adjustment!). If this procedure is successful, the back focus adjustment is finished and
you can continue with step 8. If it was not successful, please carry on with Step 7.
Step 7: Repeat steps 3 ~ 6 until the focus can be adjusted throughout the zoom range.
When using a zoom lens, the focus does not need to be adjusted again once the back
focus adjustment has been completed. This does not apply to vario lenses.
Step 8: Tighten the back focus ring's retaining screw to fix the back focus adjustment.
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