Whats ISO for on the GH1?

Pietro Impagliazzo said:
No Frausto, it's the other way around.

+6dBs over what? What is 0db? What the manufacturer determined, but you don't know what is it.

ISO is a standard! ISO100 is ISO100 in whatever system you use.
Click to expand...

When it comes to sensor output, 0db means there is no gain reduction or boost. ISO is a film sensitivity term and has nothing to do with ccd or cmos sensor output voltage.
 
fraustosound said:
You are getting into semantics. As a broadcast engineer, I have set up and shaded many a video camera, from older analog and digital SD cameras to modern HD broadcast cameras. Like you I use chip charts, WFM monitors and vectorscopes but I have yet to work with a broadcast level camera that has any form of ISO adjustment. I suppose you can find a way to convert luma voltage readings on a WFM to an ISO rating but that seems pointless from an engineering standpoint. If anything I'd call it signal-to-noise ratio before I call it ISO.

Anyway, I still would like to see proof of which ISO setting on the GH1 and GF1 is 0db gain.
Click to expand...

ISO is an illumination reference point. Native ISO is the setting for a digital sensor that produces equal DR above and below 18% gray at the camera's nominal 0 gain setting. Exposing at a different ISO for the same gain setting will trade off shadow noise for highlight protection, or highlight burnout for cleaner shadow detail. Increasing gain above the minimum setting may reset the 18% gray ISO reference point, but it also usually reduces available dynamic range. Noise is amplified and highlights clip sooner. 6dB gain is equal to a one stop shift or doubling of ISO speed. But depending on conditions one may get a better image with no gain.
Rather than specifying an ISO rating, video camera makers specify sensitivity as an f-stop rating at a particular illumination reference, usually 2000 lux or about 200fc. Matching this specification setting on a chip chart will result in 18% gray falling at 50-55IRE on a waveform monitor. One can enter these values into a programmable light meter and get an ISO reference point, but that likely will not be ideal many conditions.
If you are a gaffer prelighting a set, gain tells you nothing about the required light levels or contrast ratios one must provide to establish the look and dynamic range of the recorded scene. Light meters use ISO reference and EV scales.
Gain provides no guidance for adusting ND filters, iris, or shutter speed to achieve a particular look for a scene, shallow DOF for example if one is shooting outdoors on a bright day. If you know your camera's ISO sweet spot, this is much easier to plan, and you can precisely determine your exposure trade offs for the desired result.
It is much more than semantics, it is about knowing your photographic instrument, whether film or digital, to a degree that gives one more precise creative control, especially under conditions where you are shooting without studio control room instrumentation and monitoring conditions. One cannot practically judge exposure in the field with a viewfinder or LCD to a very fine degree, and this is especially true of low end cameras. In camera meters and zebras are pretty crude too. Forget auto iris if you want anything approaching a film like look. The only practical way to get a consistent predictable film like look is with fully manual exposure techniques and intimate knowledge of the characteristics of your camera.
 
I would agree with all that you mention here, but I'd really still just love to know the native ISO of the GH1. Regardless of if we are approaching from a video engineering background or a film background, we still need to know the native ISO of the camera, so we can squeeze the best performance out of it.
 
doccutter said:
I would agree with all that you mention here, but I'd really still just love to know the native ISO of the GH1. Regardless of if we are approaching from a video engineering background or a film background, we still need to know the native ISO of the camera, so we can squeeze the best performance out of it.
Click to expand...

Agreed. Wish I could help more with that question.
 
I cannot disagree with anything you said Razz, good info all around.

As a video engineer I mostly adjust the camera to suit the lighting whereas you adjust the lighting to suit the camera. Different approaches with the same goal in mind.
 
fraustosound said:
I cannot disagree with anything you said Razz, good info all around.

As a video engineer I mostly adjust the camera to suit the lighting whereas you adjust the lighting to suit the camera. Different approaches with the same goal in mind.
Click to expand...

Thanks, actually a bit of both, camera and lighting. The key is to know what the light is doing by using a good incident and/or spot meter, then to take best advantage of it with exposure.
I will post a couple of still frames and exposure info from my old GL2 to illustrate how well shooting video like film can work.
 
Razz16mm said:
The key is to know what the light is doing by using a good incident and/or spot meter, then to take best advantage of it with exposure.
Click to expand...

I'm usually not allowed near any lights, hehe. If it were not for my WFM and vectorscope I would have no idea what's going on. :huh:
 
You must log in or register to reply here.
Back
Top