Canon IV-S2 - Manual (Page 37)

Mounting
Before fitting the new lens into place be sure to un­
screw the Lens Dust Cap. First turn the lens counter­
clockwise a little way and then clockwise. You will
find the thread will be introduced more easily. Do
not hold the lens by any part other than the base
using the Milled Ring or the Lens Focusing Lever.
Take care not to use force if the threads bind while
turning, as you have crossed the thread.
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