Wet Macro Lens

[reign180]

Hey gang,

This may be a silly question but I'm wondering what the difference is between a standard screw in macro lens that I can buy for a camera on the surface VS a screw in macro wet lens?

They both seem to be made of glass and aluminium, and have the same threads. Is the glass different because of the properties of water?

Thanks.

 

[bvanant]

No the glass is not different but an underwater lens actually is quite complicated. A lens that has a 2x magnification in air will typically only have about 1.3x magnification in water since the index of refraction of water is significantly higher than air. A typical underwater lens has basically a flat piece of glass that touches the water and then a small air gap then the lens that does the magnification then another air gap, then another piece of flat glass. This way the magnifier is working in air rather than touching the water. You can of course use a standard air lens in the water, you just won't get much magnification.

Bill

 

[Lorenzoid]

I, too, am unfamiliar with the term "wet lens," but a couple of recent posts that used this term raised my curiosity. To me, "wet lens" sounds like a misnomer, since the lens is actually dry--suspended in air between two glass cover windows.

 

[stuartv]

Wet lens means that it is intended to be exposed to the water when you dive. It is attached to the outside of the housing that holds the camera. As opposed to a "dry" lens (I guess) that is inside the housing with the camera, so the lens itself never gets wet.

And the wet dome lenses you see are filled with air, which stays inside the lens when under water, but the front and back glass (or plastic) are exposed to the water when you dive. And you have to have water between the front of the housing and the back side of the Wide Angle wet lens in order for it to work.

For macro lenses, I'm kind of surprised (by the OP) that the threads are the same. The cameras and housings I have looked at have bigger threads on the housing than what is on the front of the camera itself. So, a wet macro lens that screws onto the housing would not be the same size as a "dry" macro add-on lens that is intended to screw onto the end of a regular lens.

I think Bill's response is a little misleading. The glass is not different in a physical composition sense. It is different (in simplistic terms) in its shape. Because water refracts differently than air. So, as Bill said, the same lens would not provide the same magnification under water. Or, conversely, a wet lens that provides X magnification and a dry lens that provides the same magnification would not be the same size/shape at all.

 

[bvanant]

I think it is more than a shape difference. Typically you have 3 elements in an underwater diopter. Two outside lenses/pieces of glass that touch water and a magnifier on the inside that is in contact with air. If you simply take even a very good air diopter like the Marumi you can get 2x magnification in air but using it in water you will only get 1/3 of that or less (depends on the index of refraction of the glass in the lens).

Bill

 

[Lorenzoid]

I think it is more than a shape difference. Typically you have 3 elements in an underwater diopter. Two outside lenses/pieces of glass that touch water and a magnifier on the inside that is in contact with air. If you simply take even a very good air diopter like the Marumi you can get 2x magnification in air but using it in water you will only get 1/3 of that or less (depends on the index of refraction of the glass in the lens).

Bill

Okay, newbie here, trying to learn the terminology. I have seen the term "diopter" used as you do, to refer to some sort of physical lens device. However, the only definitions of "diopter" I can find use it to refer to a unit of measurement. For example: the definition of diopter. What is this other definition that divers seem to use, and where did it come from?

 

[stuartv]

Okay, newbie here, trying to learn the terminology. I have seen the term "diopter" used as you do, to refer to some sort of physical lens device. However, the only definitions of "diopter" I can find use it to refer to a unit of measurement. For example: the definition of diopter. What is this other definition that divers seem to use, and where did it come from?

My understanding, just from reading and interpreting in context, is that u/w photographers say "diopter" and the are talking about a wet lens that adds on to the housing that essentially functions as a magnifying glass. They are rated in numbers like "+5" or "+8" or "+10" (or similar). I think those ratings are actually the diopter measurements. So, a "+10 diopter" is a lens that attaches to your housing (that you would use when doing macro photography) that gives you more magnification (than without or than with, say, a +5 diopter).

 

[Lorenzoid]

My understanding, just from reading and interpreting in context, is that u/w photographers say "diopter" and the are talking about a wet lens that adds on to the housing that essentially functions as a magnifying glass. They are rated in numbers like "+5" or "+8" or "+10" (or similar). I think those ratings are actually the diopter measurements. So, a "+10 diopter" is a lens that attaches to your housing (that you would use when doing macro photography) that gives you more magnification (than without or than with, say, a +5 diopter).

Thanks. I think I've got it now. "Diopter" is photographer shorthand for "dioptric lens." For example: Canon Diopters | B&H Photo Video. The product is a "Canon Dioptric Adjustment Lens." But the heading on the page uses the apparently common shorthand term: "Canon Diopters."

 

[stuartv]

Thanks. I think I've got it now. "Diopter" is photographer shorthand for "dioptric lens." For example: Canon Diopters | B&H Photo Video. The product is a "Canon Dioptric Adjustment Lens." But the heading on the page uses the apparently common shorthand term: "Canon Diopters."

Interesting that all those are lenses to go on the viewfinder, not lenses to affect the pictures you're taking.

This is a typical u/w photographer's "diopter":

SubSee +10 diopter

 

[Lorenzoid]

I see. Looks like SubSee also uses the word "diopter" by itself as shorthand for the product labeled "magnifier." So the full name of the thing would be a "+10 diopter magnifier" or "+10 diopter close-up lens." Anyway, if someone uses the term, I now know what they mean: a magnifying lens.