Velocity Reviews > Water immersion: increase DOF

# Water immersion: increase DOF

Chris Malcolm
Guest
Posts: n/a

 12-30-2009
NameHere <(E-Mail Removed)> wrote:
> On Tue, 29 Dec 2009 21:39:08 +1300, Eric Stevens <(E-Mail Removed)>
> wrote:

>>The speed of light in water is less than it is in air.

> Which leads to the question, how can the speed of light ever be used as a
> mathematical constant? Since there's no such thing as a perfect vacuum,
> there's no such thing as the constant "C" known as the speed-of-light. It's
> all opinion, no matter which way you look at it.

It's not a mathematical constant, it's a physical constant. And the
same goes for all the fundamental basic constants of physics. Did you
go to one of those modern schools where they don't teach science?

--
Chris Malcolm

Chrlz
Guest
Posts: n/a

 12-31-2009
On Dec 31, 6:56*am, Eric Stevens <(E-Mail Removed)> wrote:
> On Wed, 30 Dec 2009 05:08:01 -0800 (PST), Chrlz
>
>
>
>
>
> <(E-Mail Removed)> wrote:
> >On Dec 29, 6:39*pm, Eric Stevens <(E-Mail Removed)> wrote:
> >> On Mon, 28 Dec 2009 20:36:02 GMT, (E-Mail Removed) (Harold

>
> >> keller) wrote:
> >> >Someone once told me that one effect of photographing live fish in a
> >> >glass aquarium is that the refractive index of the water somehow
> >> >increases the depth of field.

>
> >> >Has anyone else heard of this? Does it sound plausible?

>
> >> The speed of light in water is less than it is in air. The effect is
> >> to longitudinally compress the geometry of light rays in front of the
> >> lens. Everything gets compressed, including the depth of field.

>
> >> As far as your question goes, the actual depth of field is reduced but
> >> the apparent depth of field is increased. I am sure that answer will
> >> leave you increasingly confused. * *

>
> >????
> >Indeed it does...!

>
> >Eric, can you provide some links/references/whatever on this subject?
> >Perhaps even a diagram of this 'longitudinal compression of light
> >rays' and how it then results in increased dof? *Or a modified dof
> >formula, given the existing one has no refractive index component?
> >Surely, given the amount of specialised underwater cameras/lenses that
> >are out there, such a thing would exist...

>
> Its not quite what you asked for but I found this:http://www.phy.ntnu.edu..tw/ntnujava...hp?topic=378.0
>
> Its fun but you need to be able to run JAVA
>
> Eric Stevens

Thanks, Eric, that's an interesting sim. I understand the magnifying/
foreshortening effect... but I'm intrigued on what sort of 'true',
measurable, depth of field change occurs.

It's interesting that the magnifying effect of water is often referred
to, and people with myopia (shortsightedness) report seeing better
underwater (eg, me..). But rectifying myopia, normally, requires a
*de*magnifying effect..

That does all suggest a true increase in perceived depth of field, and
underwater photography sites.. I'm just trying to tie this all
together a little more scientifically/mathematically.

Eric Stevens
Guest
Posts: n/a

 12-31-2009
On Wed, 30 Dec 2009 16:38:11 -0800 (PST), Chrlz
<(E-Mail Removed)> wrote:

>On Dec 31, 6:56*am, Eric Stevens <(E-Mail Removed)> wrote:
>> On Wed, 30 Dec 2009 05:08:01 -0800 (PST), Chrlz
>>
>>
>>
>>
>>
>> <(E-Mail Removed)> wrote:
>> >On Dec 29, 6:39*pm, Eric Stevens <(E-Mail Removed)> wrote:
>> >> On Mon, 28 Dec 2009 20:36:02 GMT, (E-Mail Removed) (Harold

>>
>> >> keller) wrote:
>> >> >Someone once told me that one effect of photographing live fish in a
>> >> >glass aquarium is that the refractive index of the water somehow
>> >> >increases the depth of field.

>>
>> >> >Has anyone else heard of this? Does it sound plausible?

>>
>> >> The speed of light in water is less than it is in air. The effect is
>> >> to longitudinally compress the geometry of light rays in front of the
>> >> lens. Everything gets compressed, including the depth of field.

>>
>> >> As far as your question goes, the actual depth of field is reduced but
>> >> the apparent depth of field is increased. I am sure that answer will
>> >> leave you increasingly confused. * *

>>
>> >????
>> >Indeed it does...!

>>
>> >Eric, can you provide some links/references/whatever on this subject?
>> >Perhaps even a diagram of this 'longitudinal compression of light
>> >rays' and how it then results in increased dof? *Or a modified dof
>> >formula, given the existing one has no refractive index component?
>> >Surely, given the amount of specialised underwater cameras/lenses that
>> >are out there, such a thing would exist...

>>
>> Its not quite what you asked for but I found this:http://www.phy.ntnu.edu.tw/ntnujava/...hp?topic=378.0
>>
>> Its fun but you need to be able to run JAVA
>>
>> Eric Stevens

>
>Thanks, Eric, that's an interesting sim. I understand the magnifying/
>foreshortening effect... but I'm intrigued on what sort of 'true',
>measurable, depth of field change occurs.
>
>It's interesting that the magnifying effect of water is often referred
>to, and people with myopia (shortsightedness) report seeing better
>underwater (eg, me..). But rectifying myopia, normally, requires a
>*de*magnifying effect..
>
>That does all suggest a true increase in perceived depth of field, and
>underwater photography sites.. I'm just trying to tie this all
>together a little more scientifically/mathematically.

A standard diagram of the way a camera works has rays of light coming
from the point of focus on the object and being bent where they pass
through the lens. Hopefully they are focussed to a point where they
meet the focal plane. I won't go into all the hoopla about depth of
field but in the real world it is theoretically possible to put in
markers at the front and rear edges respectively of the in-focus
field.

Now without changing the camera setup in any way, consider what
happens when you are photographing the inside of a fish tank through
its glass sides. The bending of the light rays as they leave the water
causes the point at which they focus on the object to be brought
closer to the camera. Yet, as far as the camera is concerned the rays
of light are still entering the lens at exactly the same angle as
before. But, if you put in markers at the front and back of the
in-focus field you will discover that they are both closer to the
camera and closer together than in the earlier situation when the
light rays were entirely through air.

If you then reach into the top of the tank with a pair of calipers or
similar and then measure their spread once you have got them out of
the water you will find the depth of focus is less than it was in air.
If the depth of field in air was (say) 10cm your calipers might tell
you (again, say) that the actual depth of field in water is only 8cm.
That's why I said "the actual depth of field is reduced".

If you now look at things from the point of view of the camera. The
light rays entering the camera still do so at the original angle and
the camera still thinks (do cameras think?) that the depth of field,
as it appears to the camera, is 10cm. But the actual depth of field
really is still only 8cm. That's why I said the "apparent depth of
field is increased" (over and above the actual depth of field). This
would be much easier to explain if I could draw a diagram.

Eric Stevens

NameHere
Guest
Posts: n/a

 12-31-2009
On Thu, 31 Dec 2009 23:50:28 +1300, Eric Stevens <(E-Mail Removed)>
wrote:

>On Wed, 30 Dec 2009 16:38:11 -0800 (PST), Chrlz
><(E-Mail Removed)> wrote:
>
>>On Dec 31, 6:56*am, Eric Stevens <(E-Mail Removed)> wrote:
>>> On Wed, 30 Dec 2009 05:08:01 -0800 (PST), Chrlz
>>>
>>>
>>>
>>>
>>>
>>> <(E-Mail Removed)> wrote:
>>> >On Dec 29, 6:39*pm, Eric Stevens <(E-Mail Removed)> wrote:
>>> >> On Mon, 28 Dec 2009 20:36:02 GMT, (E-Mail Removed) (Harold
>>>
>>> >> keller) wrote:
>>> >> >Someone once told me that one effect of photographing live fish in a
>>> >> >glass aquarium is that the refractive index of the water somehow
>>> >> >increases the depth of field.
>>>
>>> >> >Has anyone else heard of this? Does it sound plausible?
>>>
>>> >> The speed of light in water is less than it is in air. The effect is
>>> >> to longitudinally compress the geometry of light rays in front of the
>>> >> lens. Everything gets compressed, including the depth of field.
>>>
>>> >> As far as your question goes, the actual depth of field is reduced but
>>> >> the apparent depth of field is increased. I am sure that answer will
>>> >> leave you increasingly confused. * *
>>>
>>> >????
>>> >Indeed it does...!
>>>
>>> >Eric, can you provide some links/references/whatever on this subject?
>>> >Perhaps even a diagram of this 'longitudinal compression of light
>>> >rays' and how it then results in increased dof? *Or a modified dof
>>> >formula, given the existing one has no refractive index component?
>>> >Surely, given the amount of specialised underwater cameras/lenses that
>>> >are out there, such a thing would exist...
>>>
>>> Its not quite what you asked for but I found this:http://www.phy.ntnu.edu.tw/ntnujava/...hp?topic=378.0
>>>
>>> Its fun but you need to be able to run JAVA
>>>
>>> Eric Stevens

>>
>>Thanks, Eric, that's an interesting sim. I understand the magnifying/
>>foreshortening effect... but I'm intrigued on what sort of 'true',
>>measurable, depth of field change occurs.
>>
>>It's interesting that the magnifying effect of water is often referred
>>to, and people with myopia (shortsightedness) report seeing better
>>underwater (eg, me..). But rectifying myopia, normally, requires a
>>*de*magnifying effect..
>>
>>That does all suggest a true increase in perceived depth of field, and
>>underwater photography sites.. I'm just trying to tie this all
>>together a little more scientifically/mathematically.

>
>A standard diagram of the way a camera works has rays of light coming
>from the point of focus on the object and being bent where they pass
>through the lens. Hopefully they are focussed to a point where they
>meet the focal plane. I won't go into all the hoopla about depth of
>field but in the real world it is theoretically possible to put in
>markers at the front and rear edges respectively of the in-focus
>field.
>
>Now without changing the camera setup in any way, consider what
>happens when you are photographing the inside of a fish tank through
>its glass sides. The bending of the light rays as they leave the water
>causes the point at which they focus on the object to be brought
>closer to the camera. Yet, as far as the camera is concerned the rays
>of light are still entering the lens at exactly the same angle as
>before. But, if you put in markers at the front and back of the
>in-focus field you will discover that they are both closer to the
>camera and closer together than in the earlier situation when the
>light rays were entirely through air.
>
>If you then reach into the top of the tank with a pair of calipers or
>similar and then measure their spread once you have got them out of
>the water you will find the depth of focus is less than it was in air.
>If the depth of field in air was (say) 10cm your calipers might tell
>you (again, say) that the actual depth of field in water is only 8cm.
>That's why I said "the actual depth of field is reduced".
>
>If you now look at things from the point of view of the camera. The
>light rays entering the camera still do so at the original angle and
>the camera still thinks (do cameras think?) that the depth of field,
>as it appears to the camera, is 10cm. But the actual depth of field
>really is still only 8cm. That's why I said the "apparent depth of
>field is increased" (over and above the actual depth of field). This
>would be much easier to explain if I could draw a diagram.
>
>
>
>Eric Stevens

LOL!!! And you think this doofus is going to understand what you just said?
The very same thing has already been explained at least 5 different ways.
You and I are being TROLLED.

But if you insist in a "diagram":

With water:

camera-> glass|water fish fish fish fish water|glass

No water

camera-> glass|air fish fish fish fish air|glass

replace "fish" in the second example with "dead fish" due to being only in
air, "fish" was only used to keep the ASCII spacing correct.

Reading USENET is like subjecting one's self to retarded kindergartner's.