Velocity Reviews > Water immersion: increase DOF

# Water immersion: increase DOF

Harold keller
Guest
Posts: n/a

 12-28-2009
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?

Harold Keller

Eric Stevens
Guest
Posts: n/a

 12-29-2009
On Mon, 28 Dec 2009 20:36:02 GMT, http://www.velocityreviews.com/forums/(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.

Eric Stevens

NameHere
Guest
Posts: n/a

 12-29-2009
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.

Ray Fischer
Guest
Posts: n/a

 12-29-2009
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.

LOL! So if your opinion is that the speed of light is 1000mph then it
must be so? You're pretty silly.

--
Ray Fischer
(E-Mail Removed)

Harold keller
Guest
Posts: n/a

 12-29-2009
>>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.
>
>
>
>Eric Stevens

Do you mean it is reduced within the water, but appears greater from
outside the aquarium/water?

On a practical level, if my camera is outside of the aquarium, and I
am photogrpahing fish swimming inside it, does the DOF become less
critical, or increased, in proportion to the refractive index of
water?

Harold Keller

NameHere
Guest
Posts: n/a

 12-29-2009
On Tue, 29 Dec 2009 13:34:37 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.
>>
>>
>>
>>Eric Stevens

>
>
>Do you mean it is reduced within the water, but appears greater from
>outside the aquarium/water?
>
>On a practical level, if my camera is outside of the aquarium, and I
>am photogrpahing fish swimming inside it, does the DOF become less
>critical, or increased, in proportion to the refractive index of
>water?
>
>Harold Keller

Let's see if we can explain this in a way you'll understand.

Anything within the water will have the distances between them
foreshortened. Meaning, all subjects within the water will appear closer
and more compressed, back to front.

Let's, for the sake of argument, suppose you have set your camera to have a
useful DOF of 3 ft. for your chosen subject distances, of 2 to 5 ft. away
from your camera lens. Outside of that aquarium all subjects from 2 to 5
ft. will be in useful focus. Let's say the aquarium itself is 3 ft. in
depth, front to back. But due to the refraction of water it will appear to
have a depth (front to back) of only 2 ft. (Slight exaggeration for
explanation only.) Therefore, everything within that tank will be in focus,
as well as anything one foot in front of the tank will still fit within
your 3 ft. DOF range (you still have 1 ft. of DOF to use up, 2+1=3). In
effect, you are now getting a 4 ft. DOF range because 3 ft. of the
available distance has been compressed to a 2 ft. depth by the refraction
of water.

It matters not if your camera is within the water or outside of the water.
What matters are any subjects within the water. All of them will appear to
have their distances between each other more compressed, compared to the
same distances they would all have outside of the water. Therefore, the
useful DOF set by your camera's optics becomes less critical for all
subjects within the water.

On an even more practical level, I have photographed many fish in aquariums
in the past (as well as in their native environments). Never did I concern
myself with this issue because it's all relative to each subject, framing,
distance, and light levels at the time for each photograph, no two
circumstances ever the same. I just previewed the DOF in my viewfinder,
selected a useful aperture, and took their images. Are you asking this
again because you really have a need for this information and truly can't
grasp what is happening? Or are you just another troll thinking up silly
questions and feigning stupidity for the attention it will bring to you.

Chrlz
Guest
Posts: n/a

 12-30-2009
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...

nm5k@wt.net
Guest
Posts: n/a

 12-30-2009
On Dec 29, 7:34*am, (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. * *

>
> >Eric Stevens

>
> Do you mean it is reduced within the water, but appears greater from
> outside the aquarium/water?
>
> On a practical level, if my camera is outside of the aquarium, and I
> am photogrpahing fish swimming inside it, does the DOF become less
> critical, or increased, *in proportion to the refractive index of
> water?
>
> Harold Keller

I don't think it really matters much. The camera will see the same
thing your eyes are seeing, so it shouldn't be much of an issue.
I took a picture of a tank about three weeks ago and it was basically
point and shoot. Also took some HD video of it. That came out real
well.
Here is one example.. Not the greatest picture as I was just grabbing
a couple of snaps off it, but as you can see, the camera saw the same
thing my eyes did, so not much to worry about as far as taking
pictures
of it.
http://home.comcast.net/~disk100/fish.jpg

MikeWhy
Guest
Posts: n/a

 12-30-2009
(E-Mail Removed) wrote:
> On Dec 29, 7:34 am, (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.

>>
>>> Eric Stevens

>>
>> Do you mean it is reduced within the water, but appears greater from
>> outside the aquarium/water?
>>
>> On a practical level, if my camera is outside of the aquarium, and I
>> am photogrpahing fish swimming inside it, does the DOF become less
>> critical, or increased, in proportion to the refractive index of
>> water?
>>
>> Harold Keller

>
> I don't think it really matters much. The camera will see the same
> thing your eyes are seeing, so it shouldn't be much of an issue.

The liquid/air interface refracts light and so acts as a lens, and so
changes the effective focal length. Anecdotally, wearing a mask or goggles
underwater without corrective lenses lessens the effect of my myopia. The
water serves to shorten the effective focal length. It would be good to see
an analysis.

Eric Stevens
Guest
Posts: n/a

 12-30-2009
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