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Base ISO Question

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Kevin Camin
Base ISO Question
on Apr 3, 2017 at 6:15:03 pm

It is my understanding that base ISO is where the sensor's signal is not be amplified. I'm still having issues with noise on footage I receive from cameras where the footage was shot at a base ISO. Does shooting at a lower ISO have advantages on these cameras--for example, if the camera had a base ISO of 800, would shooting at 400 or 100 somehow produce a less noisy image?

Best regards,

Kevin Camin


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john sharaf
Re: Base ISO Question
on Apr 3, 2017 at 8:20:03 pm

HI Kevin,

Good instinct! Lowering the ISO does lower the noise.

Of course the other unintended result is to raise the middle gray so that there's less above and more below.

Manufacturers typically rate the nominal ISO to be either at an acceptable (to them) level of noise and/or so the middle gray allows an equal number of stops above and below.

Some brands are noisier than others, and reflect both the quality of the sensor itself and the subsequent amplification.

The exception is the Panasonic Varicam, which has "Dual Native ISO" technology of mothe 800 and 5000 with one dB of noise difference.

JS



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Kevin Camin
Re: Base ISO Question
on Apr 3, 2017 at 8:37:19 pm

Thanks, John!

One question to you or anyone else. If a base ISO is an unamplified sensor capture, what happens at a lower ISO than the base ISO? Is the sensor just less sensitive so with that comes less noise?

Best regards,

Kevin Camin


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Gary Huff
Re: Base ISO Question
on Apr 3, 2017 at 10:30:30 pm

[Kevin Camin] "for example, if the camera had a base ISO of 800, would shooting at 400 or 100 somehow produce a less noisy image?"

The answer is: it depends.

Noise comes from starving a sensor of light, not merely from the amplification of the sensor. Some cameras handle underexposed areas really well (C300 Mark II, A7S Mark II). Some cameras do not handle underexposed areas well at all (GH4). If you underexpose anything on a GH4, you get noise. Why would you underexpose? Well, some things actually [i]are[/i] dark, and you might want more contrast if you're shooting to get as close to the final image as possible. This is where a waveform monitor comes in handy because you can actually see if you're underexposing anything.


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Kevin Camin
Re: Base ISO Question
on Apr 4, 2017 at 2:28:44 am

Gary,

The situation would be the base ISO is say, 800, but we decide to shoot at 400 or 200 or 100 in an attempt to reduce the noise. We would be doing a proper exposure by using more x2, x4 or x8 the amount of light we would have at 800.

I was just wondering since the sensor doesn't amplify at base ISO 800, what is it doing under that ISO, and would that really provide a less noisy image, provided we are lighting things properly.

Thanks for your time on this! Much appreciated. : )

Best regards,

Kevin Camin


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Gary Huff
Re: Base ISO Question
on Apr 4, 2017 at 12:02:54 pm

[Kevin Camin] "I was just wondering since the sensor doesn't amplify at base ISO 800, what is it doing under that ISO, and would that really provide a less noisy image, provided we are lighting things properly."

The answer is: it depends.

Noise comes from starving a sensor of light, not merely from the amplification of the sensor. Some cameras handle underexposed areas really well (C300 Mark II, A7S Mark II). Some cameras do not handle underexposed areas well at all (GH4). If you underexpose anything on a GH4, you get noise. Why would you underexpose? Well, some things actually [i]are[/i] dark, and you might want more contrast if you're shooting to get as close to the final image as possible. This is where a waveform monitor comes in handy because you can actually see if you're underexposing anything.


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Kevin Camin
Re: Base ISO Question
on Apr 4, 2017 at 2:20:10 pm

I don't think I'm starving the sensor of light if I'm lighting things correctly.

My example is that the base ISO is 800. I decide to shoot at ISO 100. I pump enough light into the scene to get a proper exposure. I don't think I'm starving the sensor of light. My question is why would this produce less noise. It's not amplifying the signal at 800 or 100. What is the driver in this situation.

Best regards,

Kevin Camin


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Gary Huff
Re: Base ISO Question
on Apr 4, 2017 at 10:26:21 pm
Last Edited By Gary Huff on Apr 5, 2017 at 12:11:23 am

[Kevin Camin] "I don't think I'm starving the sensor of light if I'm lighting things correctly."

Then your scene would have low contrast.

[Gary Huff] "Why would you underexpose? Well, some things actually [i]are[/i] dark, and you might want more contrast if you're shooting to get as close to the final image as possible."

Think of shooting an interview against duvetine. You aren't going to "properly" expose the duvetine to keep it from being black in the image...you want it to look black and you probably don't want any of the details (wrinkles, stains, etc.) that lighting it would showcase. Some cameras will handle this fine, otherwise will be noisy because of the way you are exposing.

[Kevin Camin] "My question is why would this produce less noise. "

Because the ISO rating of the camera has nothing to do with it. The ISO rating of my C300 Mark II is rated for 800 ISO because that is the amplification of the sensor where the DR is best. When shooting Clog 2, I cannot go lower. Clog 1 is rated at 400 ISO, which I suspect is the native of the camera overall.


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Robin Probyn
Re: Base ISO Question
on Jun 23, 2017 at 11:14:21 am

you can only actually raise the noise level by over exposing the image.. say 1 or 2 stops and correcting in post.. your not changing the sensitively of the sensor..



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