Why only flat glass under water?

[Genghis Pwn]

I bought some water-tight goggles once that were curved, but when I went underwater, I couldn't see anything. It was totally blurry. I noticed later that all goggles and masks designed to be used underwater have flat surfaces you look through.

Can you only see through flat glass underwater?

Bonus question: How come you can see sharks and fish at aquariums when you walked through those round underwater glass tubes?

[jj]

Originally posted by Genghis Pwn
I bought some water-tight goggles once that were curved, but when I went underwater, I couldn't see anything. It was totally blurry. I noticed later that all goggles and masks designed to be used underwater have flat surfaces you look through.

Can you only see through flat glass underwater?

Bonus question: How come you can see sharks and fish at aquariums when you walked through those round underwater glass tubes?

The answer depends very much on specifics, but in fact since the index of refraction is much different between air and water, a curved glass that may have neutral or nearly neutral properties in air may amount to a massive correction underwater, i.e. it may have made you very near or far-sighted.

Since I don't know the shapes and don't have the time to figure out which, I can't say.

The big tunnels you are in in demo tanks have less curvature, generally, and they are much farther from your eye, putting them in the far (image) side of the field.

[Crossbow]

Originally posted by Genghis Pwn
I bought some water-tight goggles once that were curved, but when I went underwater, I couldn't see anything. It was totally blurry. I noticed later that all goggles and masks designed to be used underwater have flat surfaces you look through.

Can you only see through flat glass underwater?

Bonus question: How come you can see sharks and fish at aquariums when you walked through those round underwater glass tubes?

It sounds to me as if there was something wrong with the goggles as opposed to the shape of the lenses.

I have used scuba masks with flat lenses and curved lenses and I have not had trouble seeing with either one. However, I have found that many swimming goggles use plastic lenses that are easily fogged and I expect that may be the source of your problem.

[Soapy Sam]

A friend who (like me) is short sighted , bought a pair of optically corrected (ie prescription) goggles to use in the local swimming pool. He found that while he could see well in air (to read the clock on the wall for instance), his underwater vision was actually worse than before. He took them back to the supplier, who said- "We didn't realise you wanted to use them underwater." This sounds silly at first, but is less so when you think about what people actually look at in a pool.

So to anyone going that route- make sure you specify what you want to use them for. (Watch the girls on the poolside or look for pennies on the bottom).I imagine they can do bi- or vari-focals.

Since waterproof watches are cheap, I don't think I'll bother.

[Genghis Pwn]

Originally posted by Crossbow


It sounds to me as if there was something wrong with the goggles as opposed to the shape of the lenses.

I have used scuba masks with flat lenses and curved lenses and I have not had trouble seeing with either one. However, I have found that many swimming goggles use plastic lenses that are easily fogged and I expect that may be the source of your problem.

No, I don't think curved lenses work AT ALL underwater. Mt vision was completely blurred, not fogged. If you look at swimming googles, they are rounded, but they always have a flat surface that you actually look through. Same with scuba googles. Always flat.

[Agammamon]

Part of the problem is that in a curved goggle, unless care is taken to match, the curvature of the outer and inner surface is different. This refracts the light significantly more than a flat pane.

[malaka]

Originally posted by Genghis Pwn
Always flat.

Sometimes (http://www.bestpriceontv.com/Outdoor%2DSports%2FWatersports%2FSwimming%2FEyewea r/CJP891095/Aqua%2DSphere%2DKids%2DSeal%2DSwim%2DMask.htm) curved. (http://www.aquasphere.it/eng/goggles/main.htm)

[c0rbin]

I was told in my scuba diving class a couple years ago that things appear 30% larger under water due to the lense affect of water.

I am not an authority so take that as it is...an anecdote.

[Genghis Pwn]

Originally posted by malaka


Sometimes (http://www.bestpriceontv.com/Outdoor%2DSports%2FWatersports%2FSwimming%2FEyewea r/CJP891095/Aqua%2DSphere%2DKids%2DSeal%2DSwim%2DMask.htm) curved. (http://www.aquasphere.it/eng/goggles/main.htm)

The first ones you cannot see through underwater. The website says they are for "watersports activities"... aka, jetskiing, windsurfing, etc. I don't think they will work to see clearly underwater.

The second googles have flat surfaces through which to see. Look closely.

[Doubt]

All of these masks are curved and work quite well. (I own one.)

Good for swimming, but not diving off starting blocks.

Not for Scuba, since your nose is outside the mask.

http://www.sealmask.com/products/ironman/ironman.html#

[Genghis Pwn]

Again, the lenses do not appear to be curved...

http://www.sealmask.com/products/ironman/ir_images/gl_masks/IR_mrsil_glow.jpg

[_Q_]

Originally posted by jj


The answer depends very much on specifics, but in fact since the index of refraction is much different between air and water, a curved glass that may have neutral or nearly neutral properties in air may amount to a massive correction underwater, i.e. it may have made you very near or far-sighted.

Since I don't know the shapes and don't have the time to figure out which, I can't say.

The big tunnels you are in in demo tanks have less curvature, generally, and they are much farther from your eye, putting them in the far (image) side of the field.

I'll go with jj here. Ignoring the material of the lens itself, an interface is being formed between air and water. The shape of that interface and the refractive indexes of the respective media are going to determine how light passes through them. The larger the radius of curvature, the less dramatic the effect.

I don't think that goggles for underwater use have to be perfectly flat - just of large enough radius of curvature that, given the relative positions of your eye, the interface, and the object being viewed, the effect doesn't trouble the wearer.

So, both the curved and not-curved people are right - get ye back to the "less filling - tastes great" issue. :)


_Q_

[biglee]

Well, these googles appear curved
http://www.divemachine.co.uk/images/masks/sealmask.jpg


This one is definately curved
http://www.divemachine.co.uk/images/masks/divator.jpg

Source http://www.divemachine.co.uk/masks.htm

[calladus]

Hey, if the mask doesn't cover the nose, then it isn't any good for diving, only for swimming fairly close to the surface! (For me, goggles hurt even when I skin dive to 12 feet or so! No equalization!)

As for lenses, I have pretty severe stigmatism, and I was too poor to get a mask custom made for my pretty radical perscription. So I used a spare pair of glasses without the arms, siliconed them into my regular (flat glass) mask (with side windows) and saw just fine underwater.

I could read my gauges, watch, and see the detail in the coral this way just fine.

I dunno why this worked, and am too lazy to pick up my physics book and figure it out before school starts again.

[Genghis Pwn]

Originally posted by biglee
[B]Well, these googles appear curved
http://www.divemachine.co.uk/images/masks/sealmask.jpg

http://www.divemachine.co.uk/images/masks/divator.jpg



The first ones look like sport goggles (jet skiiking, etc.) and the second one IS NOT CURVED!!!! You can see the mask has a flat surface!!!!!!!!!!!!!!!!!! Look closely.

[bjornart]

Originally posted by Genghis Pwn


The first ones look like sport goggles (jet skiiking, etc.) and the second one IS NOT CURVED!!!! You can see the mask has a flat surface!!!!!!!!!!!!!!!!!! Look closely.

"Multiple exlamation points, a sure sign of a deranged mind."

It's hard to see at that angle, but I think the helmet has a slightly curved surface, just much less curved than the helmet itself. The slight curvature, and the distance from the eyes (as pointed out above by others) ensures that the distortion won't be a problem for the diver.

[MRC_Hans]

The reason you need googles or a mask to see underwater is that the refraction index of water is different from that of air. This means that the lenses of your eyes wont functon properly when in contact with water. A flat pane introduces a layer of air between your eyes and the water, enabling you to see clearly. There are still some problems, though: When light passes through the pane, which has water on one side and air on the other, some refraction happens, just like when light passes the surface of water. This leads to a shortening of the view: You see objected closer than they are (look into a swimming-pool and try to judge the depth). By giving the glass pane a proper curvature, you get a lens effect which can compensate for this.

Most diving masks have flat panes, because this is the simplest. Many divers are used to the distance distortion. Also, a flat pane is less susceptible to scratches.

On a really advanced mask, however, the glass can have this curvature, with edges protruding in fron of it to protect it from scratches, like the mask in that picture.

Hans

[Doubt]

Originally posted by Genghis Pwn
Again, the lenses do not appear to be curved...

http://www.sealmask.com/products/ironman/ir_images/gl_masks/IR_mrsil_glow.jpg

They are curved. None of the sealmask products have flat lenses. They are used in place of swim goggles for improved vision. The curve helps with peripheral vision.

[Crossbow]

Originally posted by Genghis Pwn


The first ones look like sport goggles (jet skiiking, etc.) and the second one IS NOT CURVED!!!! You can see the mask has a flat surface!!!!!!!!!!!!!!!!!! Look closely.

Gee whiz GP! Just go out and look at some underwater googles and masks yourself and perhaps that will convince you that sometimes the lenses are made flat and sometimes they are made curved.