Today’s Question: When I talked to you at an event a few months ago, you mentioned a lens cap that attached magnetically. Can you remind me where I can find that lens cap?
Tim’s Quick Answer: The lens cap I’m using is from a company called Xume Adapters. They produce magnetic filter holders (which I love), as well as a lens cap (which is incredibly convenient). You can find the 77mm version of the lens cap here: http://timgrey.me/77xcap.
More Detail: To my knowledge, the lens cap is not currently available in sizes other than 77mm. And it is important to note that the lens cap is really an accessory to the filter adapters offered by Xume Adapters. So, for example, if you get a set of adapters so you can easily swap filters on a given lens, in place of a filter with a magnetic adapter you can place the Xume Adapters lens cap on the lens, provided the magnetic adapter for the filters is already attached to that lens.
In other words, the lens cap from Xume Adapters makes use of the same functionality as the filter adapters they offer. You can see the Xume Adapters in action (though only for filters, not the lens cap) in an episode of Tim Grey TV via YouTube here: