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pulling focus underwater


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#1 aurelia

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Posted 28 May 2007 - 12:55 PM

Does anyone have advice /rules for pulling focus underwater. compared to out of water, normal focus pulling
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#2 Alexander Joyce

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Posted 28 May 2007 - 01:22 PM

You could use a whip like this one.

Hydroflex

You could also perhaps use a wireless remote system. That could ofcourse make things unnecessary complicated, but it could work.

Here's a discussion on CML on shooting under water.

CML - Underwater Filming
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#3 aurelia

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Posted 28 May 2007 - 02:59 PM

You could use a whip like this one.

Hydroflex

You could also perhaps use a wireless remote system. That could ofcourse make things unnecessary complicated, but it could work.

Here's a discussion on CML on shooting under water.

CML - Underwater Filming

hi thanks for the info
i didn't mean physically, i have all the remote stuff. just meant is there some sort-of equasion to it
for example if the subject above water is 4 feet what is he below? i've heard it's differnet but i don't know the math. we will be shooting above water then going under...
thanks
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#4 Jon Kukla

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Posted 28 May 2007 - 03:14 PM

I believe it's something like 9" to the foot. Don't know which way, unfortunately, but that should be easy to find out online on in the ASC manual. I've had the privilege to watch one of the top guys in the UK pull focus wirelessly from above the water, and apparently he pulls focus by monitor, based on the size of the object in the frame.
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#5 Daniel Sheehy

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Posted 28 May 2007 - 05:02 PM

The rule of thumb they teach you when you learn to dive is that objects underwater appear 25% larger.
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#6 Alexander Joyce

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Posted 28 May 2007 - 05:03 PM

hi thanks for the info
i didn't mean physically, i have all the remote stuff. just meant is there some sort-of equasion to it
for example if the subject above water is 4 feet what is he below? i've heard it's differnet but i don't know the math. we will be shooting above water then going under...
thanks



In the ASC manual it says that for shots that transition from above water to below or vice versa one should use a flat port on the underwater housing. Now according to the manual that causes a few problems. Refraction being the biggest of them.

Refraction: The focal length of your lens increases by approx 25%. The 25% magnification produces an apparent shift of the subject towards the camera, to 3/4 it's true distance.

Radial Distortion: Progressive blur increases with large apertures on wide lenses.

Chromatic aberration: different colours slightly overlap, causing a loss of sharpness and colour saturation that is more noticable on wider lenses.

This is written by Pete Romano and is in the underwater cinematography chapter of the ASC manual.
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#7 Dominic Case

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Posted 28 May 2007 - 07:03 PM

Focus the lens at 3/4 of the measured (actual) distance.
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#8 David Mullen ASC

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Posted 28 May 2007 - 07:46 PM

"aurelia" seems to be the second person to join today who didn't read the instructions when registering about using a real first and last name.

I wonder if the instructions are clear enough? People seem to miss it all the time, even though I recall it being the first thing listed. This is from the Forum Guidelines page:

Members on this forum are required to use their full real names for their Display Name. The format to use is your first name followed by a space followed by your last/family/surname. Please capitalize the first letter of each. Accounts that do not comply will be removed and cannot be reactivated. Display names can be edited in My Controls / Change Display Name once you?re logged in.
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#9 Daniel Sheehy

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Posted 28 May 2007 - 09:47 PM

In the ASC manual it says that for shots that transition from above water to below or vice versa one should use a flat port on the underwater housing. Now according to the manual that causes a few problems. Refraction being the biggest of them.


In addition; if you are using a zoom lens, then the flat port is also best. It won't cause distortion as the focal length changes.

If however you are using prime lenses, under water only, a domed port is best, as the hemispherical shape ensures that diffraction & reflection of light incident on the lens from oblique angles is minimised.
Precise positioning of the camera in relation to the port is needed.
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