If the thumbnail is hidden on init (example: in a bootstrap carousel),

I'm using zoomy on images inside a bootstrap carousel, as they are hidden on zoomy init, lensSize evaluates to zero, so I added a fix (recalculates lensSize on show if needed).
Instead of merging this pull request, may be we should refactor zoomy to compute lensSize on show instead of on init. What do you think ? How to do it ?