Panasonic LUMIX DMC-ZS100 Owner's Manual page 174

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AF Lock only is effective in the following case:
• Manual Exposure Mode
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During Manual Focus, only AE Lock can be used.
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The subject can be focused again by pressing the shutter button halfway, even when AE is locked.
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Program Shift can be set even when AE is locked.
174
Taking pictures by locking the focus and/or exposure (AF/AE Lock)
Adjusting the focus and brightness (exposure)
ZS100
SQW0547