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Gain dBs <> ISO


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#1 Flora Dias

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Posted 13 October 2007 - 06:24 PM

Hi,
i'll be shotting with HVX next month external nights. Well I would like to know how much the increase of 1dB of gain changes the ISO of the camera. If there is a value already known for all digital cameras or if someone did any test like this.

thanks
Flora
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#2 Phil Rhodes

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Posted 13 October 2007 - 06:29 PM

Hi,

Every 6dB of gain is twice as much - so if you have an ISO100 camera and apply +6dB, it becomes an ISO200 camera, give or take a bit for CCD linearity. Apply another 6dB and it becomes an ISO400 camera.

Why do you need to know this? Rating video cameras for ISO is difficult, and using the information correctly is more difficult.

Phil
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#3 Flora Dias

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Posted 18 October 2007 - 07:40 AM

Hi, Phil. Thankx for your help. I thought i' d replied your post last week, but something i did, didn't post it.
Well, I'll have the camera one day before i shoot, and this material will be transfer to film. So, since i won't be able to make any test with it, I thought about going to the location and test (or guess), with a still digital camera what is the mininal ISO necessary to get any information there. That's why i needed the information about the gain. Since we'll be transfering the material, noise isn't what i want. I'll try to use it just the extremely necessary.

Flora



Hi,

Every 6dB of gain is twice as much - so if you have an ISO100 camera and apply +6dB, it becomes an ISO200 camera, give or take a bit for CCD linearity. Apply another 6dB and it becomes an ISO400 camera.

Why do you need to know this? Rating video cameras for ISO is difficult, and using the information correctly is more difficult.

Phil


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#4 Michelob Fedusenko

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Posted 29 November 2007 - 09:43 PM

If you are doing a film transfer then you might want to look at what the lab can do to brighten it up (expose the print longer for the darker frames). It may just save you that nasty grain, but then again, you might also lose data in the low end of the exposure. Let us know what you do and how it turns out.
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#5 Adrian Sierkowski

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Posted 29 November 2007 - 10:22 PM

From my experience the noise on the HVX with gain is ugly! Avoid gain if at all possible!
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#6 Jonathan Bowerbank

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Posted 29 November 2007 - 10:54 PM

...and this material will be transfer to film.


There's a budget for a filmout, but no budget for lights?

I don't think it's possible to increase the gain by a single dB, pretty sure it's always in 3's. But +6dB is the MOST I would go, and you can do some noise cleanup in post (but it'll still be very imperfect, noisy and soft). But ideally, you don't wanna go over +3dB.
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#7 Michelob Fedusenko

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Posted 30 November 2007 - 06:44 AM

Let us know what you decide to do and share your results.
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