Infrared can see through clothes but...

Daniella68313 · Jul 20, 2003

not through something as transparent as water??? I just realized this when taking a photo of that pool and I could not see the nice pattern underwater. The water looks like it's totaly opaque.

How is it that it can see through clothing that is opaque or semi-opaque but not through water that is so transparent?

anyone care to scratch their head on that?

Jackeroo · Jul 21, 2003

very interesting !! I'm sure a couple of guru's will satisfy our curiosity with a technical explanation LOL ... they always do !! So what's the lesson ?? Simple ... if there's anything interesting under the water .. don't shoot in infra-red

) Nice shot btw.

jack
http://www.pbase.com/jackeroo

Jola · Jul 21, 2003

I'm not an expert, but IR photography is based on detecting the IR heat waves transmitted by the objects that you take pictures of.

Cold water would typically absorb IR, and would appear dark. Warmer water may transmit IR (and appear lighter), but the temperature of the water would be uniform and the whole body of water would look similar.

If you want to see anything under water you need to measure conventional light and preferably use a polarising filter to remove surface reflections.

Jackeroo said:
very interesting !! I'm sure a couple of guru's will satisfy our
curiosity with a technical explanation LOL ... they always do !! So
what's the lesson ?? Simple ... if there's anything interesting
under the water .. don't shoot in infra-red ) Nice shot btw.

jack
http://www.pbase.com/jackeroo

Fantomas · Jul 21, 2003

Interesting comparison Daniella:

I guess the explaination is this:

In conventional photography, the light comes from the sun, travels through the water without distortion, bounces at the bottom capturing the bottom's patterns, and then, comes back to the camera, again traversing the transparent light. Thus, the camera captures the bottom patterns. The camera can't capture any water pattern, because the water didn't reflected any light.

But in IR photography, it is the objects that emmit light (IR light), not the sun. This time, the water does emmit IR light. That is why the camera captures the water. The bottom also emmits IR light, but the water probably blocks this IR light, or perhaps its just that the water is before the bottom, and thus, the camera gets more IR from the water, and you can't see the bottom.

Why clothes are transparent in IR photos? maybe because clothes have low heat capacity, and emmit low IR light. The body has plenty of heat, and thus, emmit plenty of IR light.

Daniella said:
not through something as transparent as water??? I just realized
this when taking a photo of that pool and I could not see the nice
pattern underwater. The water looks like it's totaly opaque.

How is it that it can see through clothing that is opaque or
semi-opaque but not through water that is so transparent?

anyone care to scratch their head on that?

Steve Colquhoun · Jul 21, 2003

Jola said:
I'm not an expert, but IR photography is based on detecting the IR
heat waves transmitted by the objects that you take pictures of.

Cold water would typically absorb IR, and would appear dark.
Warmer water may transmit IR (and appear lighter), but the
temperature of the water would be uniform and the whole body of
water would look similar.

If you want to see anything under water you need to measure
conventional light and preferably use a polarising filter to remove
surface reflections.

I'm certainly no expert, but I'm prety sure that IR photography is based far more on IR light as opposed to IR heat. Water always appears dark because all of the IR light is absorbed by the water. Daniella, I think the reason you cannot see the items in the water is that the IR light is going into the water and not being able to reflect off the object and make it out past the surface of the water again. Maybe under certain circumstances would there be enough IR light to pierce the water surface twice, but maybe just not here. I would like to hear someone with more scientific knowledge put in their expanation.
As always, beautiful IR shot!
--
Steve C.

Olympus c4040

Marty Schultz · Jul 21, 2003

Daniella said:
not through something as transparent as water??? I just realized
this when taking a photo of that pool and I could not see the nice
pattern underwater. The water looks like it's totaly opaque.

Water is transparent to visible light but not IR. Water absorbs IR light pretty well, so the top inch or so of the water is absorbing most of the IR and there's nothing left to reflect off stuff under the water. Many plastics do not absorb much IR, and many dyes used to make them more opaque only absorb narrow bands of IR. So, a nylon fabric may look opaque in visible light but if you used IR light it would look transparent.

Now if the water was boiling hot it would emit it's own IR, but that's entirely different, you need a camera that can see more of the IR spectrum than you see in a digicam to measure heat.

Water does allow some narrow bands of IR to pass, so if you used something like IR film you might see more of what is below the water.

--
Later,
Marty

Olympus: OM-1, C-2IOO, D-49O, D-4OZ
Canon: 1OD

http://science.widener.edu/~schultz/digipicts.html

Jackeroo · Jul 21, 2003

I knew there was a simple explanation ..!!! ROFLMAO

jack
http://www.pbase.com/jackeroo

Daniella68313 · Jul 21, 2003

no the type of infrared that we capture has nothing to do with heat.

The explanation given in the thread in the Minolta forum is that water only let through shorter wavelenghts and the blue is the only color getting at any depth. all other colors are very limited and the red is completely reflected because it cannot penetrate the water. Now we really see that the Hoya R72 does not let through blue light and it does cut off most visible light. It is still strange to think that IR can see through some totaly opaque black chothes but not through something as transparent..I was really surprised.

Jola said:
Cold water would typically absorb IR, and would appear dark.
Warmer water may transmit IR (and appear lighter), but the
temperature of the water would be uniform and the whole body of
water would look similar.

If you want to see anything under water you need to measure
conventional light and preferably use a polarising filter to remove
surface reflections.

Jackeroo said:

very interesting !! I'm sure a couple of guru's will satisfy our
curiosity with a technical explanation LOL ... they always do !! So
what's the lesson ?? Simple ... if there's anything interesting
under the water .. don't shoot in infra-red ) Nice shot btw.

jack
http://www.pbase.com/jackeroo

Click to expand...

--
Daniella
http://www.photosig.com/viewuser.php?id=26918
http://www.pbase.com/zylen
C7OO FORUM: http://www.c700uz.com

c7OOuz, Dimage-7, Tcon14tele, C210tele, Cokin-173, Grad-ND, Hoya-red-Intensifier, Hoya_R_72.

Daniella68313 · Jul 21, 2003

Steve Colquhoun said:
I'm certainly no expert, but I'm prety sure that IR photography is
based far more on IR light as opposed to IR heat.

yes you're right.

Water always

Steve Colquhoun said:
appears dark because all of the IR light is absorbed by the water.

is it absorbed or reflected? All I see is mostly reflection on the surface of that pool.

Steve Colquhoun said:
Daniella, I think the reason you cannot see the items in the water
is that the IR light is going into the water and not being able to
reflect off the object and make it out past the surface of the
water again. Maybe under certain circumstances would there be
enough IR light to pierce the water surface twice, but maybe just
not here.

hmmm I think I will experiment with more pool depth..and angle just to see.

I would like to hear someone with more scientific

Steve Colquhoun said:
knowledge put in their expanation.
As always, beautiful IR shot!
--
Steve C.

Olympus c4040

--
Daniella
http://www.photosig.com/viewuser.php?id=26918
http://www.pbase.com/zylen
C7OO FORUM: http://www.c700uz.com

c7OOuz, Dimage-7, Tcon14tele, C210tele, Cokin-173, Grad-ND, Hoya-red-Intensifier, Hoya_R_72.

Daniella68313 · Jul 21, 2003

Marty Schultz said:
Water is transparent to visible light but not IR. Water absorbs IR
light pretty well, so the top inch or so of the water is absorbing
most of the IR and there's nothing left to reflect off stuff under
the water.

but if it absorb it all, how can I see the very clear reflection on the surface of the water? It has to reflect it somehow...and I may be wrong but it if is absorb it, it can't reflect it no?

Many plastics do not absorb much IR, and many dyes used

Marty Schultz said:
to make them more opaque only absorb narrow bands of IR. So, a
nylon fabric may look opaque in visible light but if you used IR
light it would look transparent.

Now if the water was boiling hot it would emit it's own IR, but
that's entirely different, you need a camera that can see more of
the IR spectrum than you see in a digicam to measure heat.

Water does allow some narrow bands of IR to pass, so if you used
something like IR film you might see more of what is below the
water.

--
Later,
Marty

Olympus: OM-1, C-2IOO, D-49O, D-4OZ
Canon: 1OD

http://science.widener.edu/~schultz/digipicts.html

--
Daniella
http://www.photosig.com/viewuser.php?id=26918
http://www.pbase.com/zylen
C7OO FORUM: http://www.c700uz.com

c7OOuz, Dimage-7, Tcon14tele, C210tele, Cokin-173, Grad-ND, Hoya-red-Intensifier, Hoya_R_72.

Lucy · Jul 21, 2003

........reading these forum threads!

This is quite interesting......I think I now understand why the newest scanners at the airports can show naked people! Oh my.....

--
Lucy
Olympus C3020Z
http://www.pbase.com/lucy

Daniella68313 · Jul 21, 2003

Lucy said:
........reading these forum threads!

This is quite interesting......I think I now understand why the
newest scanners at the airports can show naked people! Oh my.....

they can? are they using them on people?

Lucy said:
--
Lucy
Olympus C3020Z
http://www.pbase.com/lucy

--
Daniella
http://www.photosig.com/viewuser.php?id=26918
http://www.pbase.com/zylen
C7OO FORUM: http://www.c700uz.com

c7OOuz, Dimage-7, Tcon14tele, C210tele, Cokin-173, Grad-ND, Hoya-red-Intensifier, Hoya_R_72.

Marty Schultz · Jul 21, 2003

Daniella said:
but if it absorb it all, how can I see the very clear reflection on
the surface of the water? It has to reflect it somehow...and I may
be wrong but it if is absorb it, it can't reflect it no?

Reflection is more complicated.

One way to think about it is to think of the water as a polished surface, ever see your reflection in a black object that was polished? The black object should be absorbing all the light, but the polshied surface still reflects. On a highly polished surface some of the light bounces off without really interacting with the material so it doesn't get absorbed.

I won't go into index of refration and the more complicated stuff.

--
Later,
Marty

Olympus: OM-1, C-2IOO, D-49O, D-4OZ
Canon: 1OD

http://science.widener.edu/~schultz/digipicts.html

Guy Parsons · Jul 21, 2003

Isn't it that some cloth types are more transparent to IR? I remember one ordinary indoor daylight shot with my slightly IR sensitive C-730 did once make a white blouse look very transparent, it was a back view - so no embarrasment.

I vaguely remembered that natural fibres may block IR but some synthetics are very transparent to IR.

Have you tested this at all?

When visiting airports it is probably advisable to wear aluminium foil underclothes!

Regards............ Guy

Fantomas · Jul 21, 2003

so let me get this right:

all the IR light that the camera captures, comes from the sun?, and not from the internal heat of the objects?

then, if you shoot a IR photo at night, you won't get anything?

sorry but I have no experience in this field, I was just guessing the answer

Marty Schultz said:
Daniella said:

but if it absorb it all, how can I see the very clear reflection on
the surface of the water? It has to reflect it somehow...and I may
be wrong but it if is absorb it, it can't reflect it no?

Click to expand...

Reflection is more complicated.

One way to think about it is to think of the water as a polished
surface, ever see your reflection in a black object that was
polished? The black object should be absorbing all the light, but
the polshied surface still reflects. On a highly polished surface
some of the light bounces off without really interacting with the
material so it doesn't get absorbed.

I won't go into index of refration and the more complicated stuff.

--
Later,
Marty

Olympus: OM-1, C-2IOO, D-49O, D-4OZ
Canon: 1OD

http://science.widener.edu/~schultz/digipicts.html

DeagleDave · Jul 21, 2003

You can see the design in this pic: (if it's the same pool that is)

--
-Dave
http://www.DeagleDaveAlbum.DavesPhotoAlbum.photoshare.co.nz

Ted · Jul 21, 2003

Note to self: Only use the IR filter when photographing Dry T-shirt contests...

Daniella said:
not through something as transparent as water??? I just realized
this when taking a photo of that pool and I could not see the nice
pattern underwater. The water looks like it's totaly opaque.

How is it that it can see through clothing that is opaque or
semi-opaque but not through water that is so transparent?

anyone care to scratch their head on that?

Daniella68313 · Jul 21, 2003

I have not teste chothes transparency because I have not much interest in seing wonderbra thing under shirt

but that's about all you would see. You cannot see a totaly naked person under the clothes, you can only see bits of underwear and no skin.

Guy Parsons said:
Isn't it that some cloth types are more transparent to IR? I
remember one ordinary indoor daylight shot with my slightly IR
sensitive C-730 did once make a white blouse look very transparent,
it was a back view - so no embarrasment.

I vaguely remembered that natural fibres may block IR but some
synthetics are very transparent to IR.

Have you tested this at all?

When visiting airports it is probably advisable to wear aluminium
foil underclothes!

Regards............ Guy

--
Daniella
http://www.photosig.com/viewuser.php?id=26918
http://www.pbase.com/zylen
C7OO FORUM: http://www.c700uz.com

c7OOuz, Dimage-7, Tcon14tele, C210tele, Cokin-173, Grad-ND, Hoya-red-Intensifier, Hoya_R_72.

Daniella68313 · Jul 21, 2003

Fantomas said:
so let me get this right:

all the IR light that the camera captures, comes from the sun?, and
not from the internal heat of the objects?

then, if you shoot a IR photo at night, you won't get anything?

If you shoot IR photo at night you will get a nice black frame

we cannot capture that type of heat infrared but only the near infrared that is generated by the sun and some incandescent lamps.

IR photography does not do very well in low light too..it does work in overcast sky so looks like the IR light is going through clouds:

http://www.pbase.com/image/15574481

that was taken in a totaly overcast day with a thick haze cover plus some low clouds. The shutter speed increased and the foliage is less white than in full sunlight or bright light.

Fantomas said:
sorry but I have no experience in this field, I was just guessing
the answer

Marty Schultz said:

Daniella said:

but if it absorb it all, how can I see the very clear reflection on
the surface of the water? It has to reflect it somehow...and I may
be wrong but it if is absorb it, it can't reflect it no?

Click to expand...

Reflection is more complicated.

One way to think about it is to think of the water as a polished
surface, ever see your reflection in a black object that was
polished? The black object should be absorbing all the light, but
the polshied surface still reflects. On a highly polished surface
some of the light bounces off without really interacting with the
material so it doesn't get absorbed.

I won't go into index of refration and the more complicated stuff.

--
Later,
Marty

Olympus: OM-1, C-2IOO, D-49O, D-4OZ
Canon: 1OD

http://science.widener.edu/~schultz/digipicts.html

Click to expand...

--
Daniella
http://www.photosig.com/viewuser.php?id=26918
http://www.pbase.com/zylen
C7OO FORUM: http://www.c700uz.com

c7OOuz, Dimage-7, Tcon14tele, C210tele, Cokin-173, Grad-ND, Hoya-red-Intensifier, Hoya_R_72.

Daniella68313 · Jul 21, 2003

It was taken at Hearst Castle on the California coast.

Infrared can see through clothes but...

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