PN,
I'm not sure which is #4, but I bought my optivisor about 5 or 6 years ago & it probably wasn't the top of the line edition. Since then, the double flip down lens has fallen off as well as the single right eye monocle. The only lens left is the one that is attached as part of the optivisor itself. I usually use my reading glasses under the visor. So far, the visor & reading glasses are plenty for me to see all the details on the 54mm guys I paint, even considering that my eyesight isn't what it used to be.
Mike