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Working at 2k Vs Field of view for 35mm lenses


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#1 oscar jimenez

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Posted 08 September 2008 - 09:02 AM

Hi everyone.
I was going tru some tests with a RED ONE build 15. I was testing High Speed of camera to get to know how it looked.
So camera was set at 60 fps with the equivalent of a 45 deg shutter on. the lens that I had at hand was a 18mm ( 35mm prime lens ), but somewhat it "feeled and looked" a little bit Narrower field of view that would normally do on a 35mm camera, I was so into testing the high speed of the camera that I didnt paid too much attention to this, now Im still wondering if at 2k and in a 2:1 aspect ratio of the sensor ( choosed from the menu of the camera ) would it be the
same as using 35mm lenses on a super 16 camera? that was the way it looked on the RED monitor, is it this the way it works on the RED? so my question here is that 1. If set to 4k on proy preferences will the 35mm lenses have the same field of view as they should 2. If I work at 2k will the 35mm lenses loose their original field of view or have it transformed like if it was putting them on a sup 16 camera? so they become narrower?
Another funny issue is that I was doing a water pouring at 60fps on a glass coup against black velvet and over black velvet, when I set the camera to an equivalent shutter angle of 11 degrees, suddenly part of the image turned sort of gold / brownish. Lightning was a 1200 par HMI with magnetic ballast ( that's why I choose 60 fps ) Diffussion frame with 216 and a 6x6 Bounce board on the other side, so I cant really see why reflections on the cup turned out brownish / gold. quite strange. Cam exposure set to 320 ASA so whas my meter but always checked on the Illegal color setting on the onboard monitor, exposure was very much consistant with the light meter.
Cheers and many thanks for any clues on this subject.
Oscar
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#2 Mitch Gross

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Posted 08 September 2008 - 09:25 AM

2K one the RED uses a sensor area smaller than regular 16mm.

If you close your shutter angle too far down, your exposure time narrows to a point where a unit such as a magnetic ballast HMI will show numerous artifacts including the color cast you describe.
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#3 thomas-english

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Posted 08 September 2008 - 09:32 AM

I am thinking of buying a RED to use on my s16 lenses. All the literature I have read says that you can shoot a full s16 frame at 2k. It says you can choose between 35mm, s16 2/3rd inch.

When shooting high speed I was hoping/planning on using the full s16 frame at 2k. Am I wrong?

Please explain to me the ins and outs of shooting s16 on the RED. I would really appreciate it as I am confused.
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#4 Mitch Gross

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Posted 08 September 2008 - 09:39 AM

When shooting at 2K on the RED, one is simply "windowing" a smaller portion of the sensor. This image area is smaller than that of regular 16mm. One can use 16mm, S-16, or 35mm format glass and all will cover this image area. 2/3" B4 mount lenses can be used with an adaptor which will add a very slight magnification factor to cover the 2K image area.
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#5 thomas-english

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Posted 08 September 2008 - 10:09 AM

really, so essentially my s16 lenses will have a slight magnification factor in Field of View to what I am used to on my sr2.

I could shoot full frame 4k and crop down but I would rather shoot full frame s16 at 2k.
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#6 Mitch Gross

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Posted 08 September 2008 - 01:38 PM

To mimic Super-16 image area on the RED one would shoot at something like 2.6K.
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#7 John Sprung

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Posted 08 September 2008 - 07:18 PM

On my chart, the width of Super 16 is given as 0.458". The RED chip has 4520 photosites across 0.961", so the math works out to 2154 photosites for the equivalent width, which is basically just about 2K. It's too close to worry about.



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#8 thomas-english

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Posted 09 September 2008 - 03:26 AM

So It's not as marked a FOV loss as using my s16 on the silicon imagingi camera with its 2/3rd inch chip.

Can anyone tell me the actual FOV loss relative to s16 of shooting 2k on windowed RED?

I understand that a B4 video lense covers the RED windowed chip with slight magnification. A B4 lens just about covers a s16 gate. If your saying a B4 lens has slight magnification relative to video on a windowed RED, your saying that a windowed RED chip is SMALLER than 2/3rd inch. So will have CONSIDERABLE magnification relative to s16

Edited by thomas-english, 09 September 2008 - 03:27 AM.

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#9 Mitch Gross

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Posted 09 September 2008 - 11:46 AM

The RED One at 2K will be fully covered by a regular 16mm lens. The SI-2K at 2K requires a S-16 lens for full coverage -- a regular 16mm lens will cut off in the corners. The SI-2K will be closer in image size to Super-16 than the RED One at 2K. The magnification is fairly small on the RED One and extremely small on the SI-2K.

A B4 lens projection is smaller than 16mm. It needs to be magnified to fit on either the RED One or the SI-2K.
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