The Sony FE 100mm f/2.8 Macro GM lens has a focus collar that moves forward for Autofocus (AF) and back for Manual Focus (MF).
This is fine topside but underwater it’s not so useful. In fact, on any underwater housing, there’s a chance to inadvertently bump the collar when installing the lens. And if you’re left in manual focus without a focus ring installed, you’re going to end up missing photo opportunities. This can be avoided by easily sliding on the Focus Ring Lock.
Once pushed forward in the autofocus position, the silicone ring sits in the remaining space and blocks the focus collar from moving. This lock is not intended to be pushed down into the gap, but fit just on top of it. It can be easily removed and re-attached in between dives, just be careful not to stretch it out.
If you're planning on using autofocus with this lens, buy yourself some easy insurance and save a few headaches by adding this to your lens.
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