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Old July 30th, 2008, 04:44 PM   #1
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Shooting Thru a Windshield - tips/tricks?

We are shooting a no-budget comedy short in a couple weeks, and I am wondering how it is recommend to shoot a driver/passenger through the windshield of a car.
The main thing I am worried about is reflections, but what do you recommend for camera mount systems as well? We're shooting with a sony V1u, pretty much stock.

I'm assuming you use a large sunshade or something along those lines, but if the car is moving I could see that becoming a hazard of being ripped off by wind. And the goal is to use as much natural light as possible. Thoughts?

-Jeff
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Old July 30th, 2008, 05:20 PM   #2
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Jeff,
There are some low-budget options for hood-mounting small cameras. Filmtools offers a vacuum cup based hood mount option for under $100. We used the Gripper as its called with a DVX way back when along with a tiedown kit(that was another 250 though).
As far as reflection goes, the quickest and easiest way to reduce reflection is placing a rotatable linear polarizer over your lens.
Finally, a big tip I have from experience is try to stick to an over cast day or drive the vehicle through an area that is in shade. The polarizer can really help but it can't compensate for the power of direct sunlight.
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Old July 30th, 2008, 05:58 PM   #3
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Just an idea, if you guys have a smaller B-cam, you could place it ON the dashboard and use a wide-angle adapter instead of outside, through the windshield.
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Old August 3rd, 2008, 04:10 PM   #4
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Three words:

POLARIZED LENS FILTER

This will typically eliminate or at least greatly diminish the vast majority of window reflections and are a LOT easier to rig than a large sun shade over the windshield of a moving car.

The best are those that have a dual ring free-rotation construction so that you can change the orientation of the polarization to get the best elimination of the unwanted off-axis reflected light rays.
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Old August 3rd, 2008, 06:12 PM   #5
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I bought a polarizer for this same purpose, but it wasn't strong enough. Try to get a really strong polarizer. (I don't know whether polarizers can be stacked; if they can, you'll probably need one linear and one circular polarizer).

A great alternative is to shoot from the back seat. Makes your life real easy.
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Old August 4th, 2008, 02:39 PM   #6
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Agree on the polarizer - with a circular polarizer that you can adjust, you can literally watch glass "disappear" as you rotate the filter element.

Also, Sean, yes, you CAN stack polarizers... you can use two CP to effectively block out ALL light entering the lens ( I can only guess that an LP with a CP would function similarly, don't own a LP myself)! The reason I mention this is I just experimented with this to force a shallow Depth of Focus out of a handycam! I wasn't trying to eliminate reflections, rather I was trying to force the cam iris to open up as much as possible to make the DoF as shallow as possible... the dual polarizers basically became a variable ND filter, tunable to taste!
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Old August 4th, 2008, 02:42 PM   #7
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No need to use a circular polarizer with modern video cameras. Linear will do fine.
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Old August 5th, 2008, 12:40 PM   #8
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Agree with Charles.

True circular polarizers are pretty special use devices and are hardly ever necessary these days.

IIRC, If you're using an older style camcorder that has "always on" cheap auto focus, then the circular polarizer provides some polarizer benefits while avoiding the problem of focus hunting.

One confusion I'm reading here is the difference between an actual "circular polarizer" and a linear polarizer that's built on a swivel ring to allow easy polarizer orientation - these are two different things.

Rotating an actual circular polarizer won't change anything about how it filters the light coming in the lens. That's because the polarization embedding is itself CIRCULAR - following the diameter of the lens - so rotating it does nothing. While rotating a linear polarizer will change the angle of acceptance of the light rays being passed through the filter and make a HUGE difference on filtering out scattered light reflections as are common from reflective surfaces such as water, glass, etc.

So unless your camcorder is REALLY cheap and has "always on" auto focus, stick with common linear polarizers for best results.
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Old August 12th, 2008, 12:06 PM   #9
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Quote:
Originally Posted by Bill Davis View Post
Agree with Charles.

True circular polarizers are pretty special use devices and are hardly ever necessary these days.

IIRC, If you're using an older style camcorder that has "always on" cheap auto focus, then the circular polarizer provides some polarizer benefits while avoiding the problem of focus hunting.

One confusion I'm reading here is the difference between an actual "circular polarizer" and a linear polarizer that's built on a swivel ring to allow easy polarizer orientation - these are two different things.

Rotating an actual circular polarizer won't change anything about how it filters the light coming in the lens. That's because the polarization embedding is itself CIRCULAR - following the diameter of the lens - so rotating it does nothing. While rotating a linear polarizer will change the angle of acceptance of the light rays being passed through the filter and make a HUGE difference on filtering out scattered light reflections as are common from reflective surfaces such as water, glass, etc.

So unless your camcorder is REALLY cheap and has "always on" auto focus, stick with common linear polarizers for best results.
Bill, such a device as you describe may well exist, but "circular polarizer" generally means a combination of a linear polarizer and a quarter wave plate. The output of this combination is two perpendicular electromagnetic plane waves of equal amplitude and 90 difference in phase. If it were possible to see the electric field vector, it would appear to be rotating around the direction of propogation, hence "circular polarized".
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Old August 13th, 2008, 08:31 AM   #10
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Thank you Steve for an elegantly put explanation although I will freely admit that it goes over my head (my understanding of physics is just enough to be able to do my job and not much more!)

For those like myself, this may require further clarification (and Bill, this disagrees with your statement about circular pola's deliver the same results regardless of rotation).

From Tiffen's site:

"A Circular Polarizer is a linear one to which has been added,on the side facing the camera, a quarter wave "retarder." This "corkscrews" the plane of polarization, effectively depolarizing it, eliminating the problem. The Circular Polarizer otherwise functions in the same manner."

A polarizer that does not change when rotated would be pretty useless in actual practice, right? It would simply function as an ND.6...!

I've never really seen a specific listing of which camcorders (cheap or not) have their auto-focus affected by a linear pola, but apparently there are (or were) some. And while some cameras with beam-splitters were affected, this were apparently all film cameras and the issue came with the video tap image which would black out with a linear pola in use (the film image and viewfinder image was fine), but most of these have been phased out. While 3-chip video cameras use beam splitters, they do not have problems with linear pola's. I have personally never needed a circular pola on any film or video camera I have used, it's probably safe to say that they are not needed on current models.
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Old August 13th, 2008, 04:45 PM   #11
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I probably don't need to say this, but the most important thing to do when shooting through glass is to get it CLEAN. The most insignificant layer of grime will look like a bed sheet pulled over your image when it gets hit by the sun. Clean it thoroughly inside and out. If it is an older car, the glass is probably etched by years of use and could be a problem. I polished my windshield before I did a shoot last year and it was difficult but the shot would have been useless without. If you shoot from inside the car facing out the windshield, you will need to put some black fabric on the dashboard to eliminate glare. I used gaffer tape to hold the fabric and even just the bit of gloss on good gaffer tape ruined the first shot.
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Old August 14th, 2008, 11:54 AM   #12
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Thanks all,
I'm thinking about picking up a mattebox and a pair of 4x4 linear polarizers. Because the mattebox has one rotating filter frame and one stationary, that would work to rotate the polarizers right? I'd assume it's pretty much the same. As well, I think we're going to extensively clean the windshield and try to shoot on a less-sunny day. I'm sure it will be posted when the whole thing is shot.
Once again, thanks for your help
-Jeff
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Old August 14th, 2008, 12:04 PM   #13
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Jeff, why are you getting two polarizers? You only need one.

I recommend the Schneider True-Pol, it's an industry standard for maximum effect.
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Old August 16th, 2008, 03:59 AM   #14
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Quote:
Originally Posted by Steve Brady View Post
Bill, such a device as you describe may well exist, but "circular polarizer" generally means a combination of a linear polarizer and a quarter wave plate. The output of this combination is two perpendicular electromagnetic plane waves of equal amplitude and 90 difference in phase. If it were possible to see the electric field vector, it would appear to be rotating around the direction of propogation, hence "circular polarized".
I'm pretty sure this isn't the ONLY piece of quasi technical mis-information that's been rattling around in my brain all these years.

Mea Culpa - and thanks Steve for the MUCH better explanation.

(I guess I should have studied more Physics and less Mass Comm back my school days!)

And I second the advice about needing only one polarizer. Generally, if you stack two polarizers up, and rotate one, you just get to a point where the double polarization of the light just eliminates all the light entering the lens. Useful only if your video is entitled "Black cow in a coal mine - a video study"

;)
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Old August 16th, 2008, 03:35 PM   #15
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Yep - stacking polarizers gives you the ability to go completely black... or make your camera open up its iris to the max... still playing with the possibilites... first tests were promising on improving DoF on an HD handycam.
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