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Canon VIXIA Series AVCHD and HDV Camcorders
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Old December 2nd, 2012, 11:16 PM   #1
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Hf g10 gain = iso

Thought the title would get some attention. I have a nice digital light meter for photography work, and I'm wandering how I can use it with my G10. My DSLR and my meter work in ISO. THe G10 obviously works with the concept of a gain on the sensor. Does anyone have math or a formula that converts gain into ISO or something close? Otherwise I have a lot of experimentation to do.....

Thx.

-mike
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Old December 3rd, 2012, 07:21 AM   #2
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Re: Hf g10 gain = iso

Is that O'Fallon, MO? Welcome aboard.
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Old December 3rd, 2012, 10:22 AM   #3
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Re: Hf g10 gain = iso

Yup. You are correct.
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Old December 4th, 2012, 06:32 AM   #4
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Re: Hf g10 gain = iso

I believe that adding gain is a bit more like push processing in film speak, but it enables exposure at a higher (or lower) effective ISO.

ISO is a numerical factor that is used to map/convert between light level and exposure (shutter and aperture) using a meter. It is determined based on exposure needed to produce a specified image density on the film under a defined (for that film) standard development process (chemicals, time, and temperature). If you expose film at a higher than rated ISO you may need to push process it (e.g., more development time, higher developer concentration, and/or higher temperature) to obtain the same image density on the film. This push processing usually bring other artifacts with it, like increased grain and perhaps color and gamma shifts.

Film shooters typically need a light meter as an aid because one does not see the results of the exposure until the film is souped. Even Polaroid had a minute or so wait.

Because a video capera gives instant image feedback (on the monitor) it is in effect a light meter, and you see all of the image; highlights and shadows, so you can adjust expsoure on the fly to optimize the scene. A separate light meter is not needed, but may come in handy when building and lighting a set without a video camera at hand.

If you want to determin an "effective ISO" then setup the camcorder to provide the image you want, record the shutter, aperture and gain, Take a light meter reading of the scene, and then adjust the meter to show what ISO is needed to produce that shutter and aperture. Not difficult or time consuming if you have a devent light meter. At that point you have an effective ISO at that gain setting.

I believe the zero gain reflects the camcorder maker's "sweet spot" in the sensitivity curve of the sensor that provides what the manufacturere believes is the best compromise among image grain, noise, light sensitivity, color performance, shadow and highlight detail, etc. for the market segment the camcorder is trying to reach.

If you search the several forums here you will probably find various reports on effective ISO/ASA by users. From recollection, numbers around ISO300, give or take a stop or two are common
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