+4 diopter - where to get one?
Stupid question, but where can I get a +4 diopter as recommended on Ikelite's site? This is for a Tamron 28-75 mm XR LD Di (whew!) behind a Ikelite #5503.80 dome port.
"Zoom Lenses usually require addition of a +4 diopter close-up to the lens for full range operation underwater behind a dome port."
I've never used a zoom lens underwater before, so have never even seen or touched a diopter. Does it screw in like a filter? Are they lens diameter specific? Are there differences between different brands? Who the heck makes them anyway?
Any help is appreciated!
Thanks,
Ben