"wet" vs "dry" close up lens

[stepfen]

Hi guys,

I know that wide-angle wet lenses need water to operate. What about wet close-up lenses? Do they need water too? From optics point of view I can't see why. They are just a piece of (magnifying) glass.

I've seen Inon advertising their lens as being "Dual use underwater / land" so I guess dry/land lenses should be ok underwater too. Fortunately the metal ring around them seems to be made of aluminum or so, so rust won't be a problem either, I hope.

It all started recently when a fellow diver let me use one of his close up lenses (diopter 6) to try it out during a night dive. He even helped me pointing out several small creatures for me to try to shoot. It was difficult but I managed to get a couple of nice (for a newb like me) shots. Since then I am attracted to the idea to be able to shoot small things (not tiny - yet) but I also don't feel I'm hooked to macro photography to the extend justifying investing large amount of money to it. Specialized wet lenses are way too expensive for me.

I can find some cheap (~50$) sets of land lenses on eBay and carrying a lens like that just in case seems quite attractive idea to me. Of course I don't expect perfect results. Mostly I want to be able to experiment with it.

Any thoughts?

Thanks

 

[tursiops]

You need underwater close-up lenses. They have an air layer sandwiched between glass layers. This allows the magnification to be independent of whether the lens is underwater or not. Land lenses barely work underwater. Don't bother.

Summary: a lens made for use underwater will work fine on land, but not vice-versa.

 

[bvanant]

Lenses work because there is a mismatch between the medium where the light is traveling and the glass. For an air/glass interface the index of air is essentially 1 and the glass is somewhere around 1.4 (depends strongly on the glass composition). The difference is then about 0.4 in index. For water/glass the index of water is 1.33 (more or less, depends on temperature and wavelength and how much salt is in the water) so the difference is only 0.07 which is about 17.5% of the difference for air. As tursiops has said a good underwater lens has air between the water piece and the actual lens which means that for all practical purposes the good UW lenses work as well in air as in water.

Cheers
Bill

 

[stepfen]

Thanks a lot folks. That makes sense. I was hopping to give macro a (cheap) try. Seems I'll need to wait a bit more.
Thanks anyway

 

[tursiops]

Thanks a lot folks. That makes sense. I was hopping to give macro a (cheap) try. Seems I'll need to wait a bit more.
Thanks anyway

You can often find used u/w macro lens on sites like WetPixel for a decent price.

 

[outofofficebrb]

Thanks a lot folks. That makes sense. I was hopping to give macro a (cheap) try. Seems I'll need to wait a bit more.
Thanks anyway

Maybe you can get a used GoPro and then get Backscatter's Macromate Mini +10. It is a relatively inexpensive way to shoot macro for a beginner and you can get some decent video with a filter as well. When you get tired of it and want to upgrade, you can sell it - there's a great second hand market. If you love it, you can add lights and a tray....Or eventually, if you ever upgrade, you can mount it onto your camera's shoe.

Users report the Olympus TG5 does decent macro as is without an extra lens but obviously way better with one. Some things and options to consider.