Diopters

S2 Pro + Ikelite owners:

Is the +4 diopter only necessary for macro lens, or are other diopters optional?

How about other lenses - will they need the same?

Appreciate info. Am trying my best to get system ready for the ocean while waiting (Yawwwnn!) for the new Ikelite housing.

Seadeuce

I use a +4 closeup lens (sometimes called diopter) with my Nikkor 18-35ED lens with the extended dome port.

My read on the situation is that a diopter is basically just a "magnifying glass" that changes the focal distance of the lens.

Many people use diopters for "super macro" of pygmey seahorses, etc. May or may not be necessary w/ the 1.5x magnification factor of the S2.

Nexus America sells an underwater removable diopter called "Woody's Diopter" named after Woody Mahew. You can stick it on the front of the Ikelite flat port while diving if you see something especially small. http://www.nexusamerica.com/Misc/Misc.html for details.

Cheers

James

There are some good articles about diopters at the Scubageek website. They're written from a scuba photographer point of view.

In short, diopters are used to modify focusing range. They also modify focal length, but not how you might expect. Diopters in macro allow closer focusing for greater magnification. They sometimes provide greater magnification at a given distance, too, but that's actually caused by how the lens focuses internally. Diopters are not required for macro but are frequently useful.

Dome ports are another matter entirely. Scubageek has an article on dome optics that is worth reading, too. The short answer here is that the lens behind the dome must be capable of close focusing but far focusing (including infinity) is of no use. If the lens meets the close focus requirement, no diopter is used. If not, the diopter providing the least power necessary is used. For any given lens/dome combo, there is a proper diopter choice and the dome manufacturer usually specifies it.

Does that imply that you can use pretty much any lense behind a dome port, provided that the minimum focus distance of the lense meets the requirements of the dome, either natively or through the addition of a diopter?

Yes.

Yes, James is right. The centerpoint of the dome needs to be in the right spot, too. Manufacturers provide spacers for that, although I don't know the procedure for getting it right. The short focal length lenses usually work without diopters. Longer ones (and zooms) generally require them.