why not f/1.2 by Sony?

Started May 14, 2013 | Discussions thread
Great Bustard
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Re: Except...
In reply to franzel, May 17, 2013

franzel wrote:

Great Bustard wrote:.

So, f/1.2 on 1.5x puts the same total amount of light on the sensor for a given shutter speed as f/1.8 on FF, which will result in the same noise for equally efficient sensors.

Sorry, that's not true .

It is.

The amount of light is not measured across the entire sensor surface, that's not how sensivity measurement works .

I'm not talking about "sensitivity" -- I'm talking about the total amount of light falling on the sensor.

Any object of a certain brightness will always create the same exposure with a certain ISO/f-stop/shutter speed combination, on sensors of any size or quality - unless someone lies about the specs .

Correct.  But I'm not talking about brightness -- I'm talking about the total amount of light falling on the sensor.

Resulting image quality, noise, resolution, enlargment, that is a very different matter, but that discussion is not about ISO or aperture . 
Those are related to a degree, but not part of any reasonable comparison chart .

They are related in that, for equally efficient sensors, the same total amount of light falling on the sensor results in the same image noise.

The reason larger sensor systems are less noisy than smaller sensor systems is because more light falls on the sensor for a given exposure.

So, the recap:  the same aperture diameter results in the same DOF for a given framing and perspective (e.g 50mm / 1.8 = 33mm / 1.2 = 28mm).  It also results in the same total amount of light falling on the sensor for a given shutter speed, which results in the same noise for equally efficient sensors.

The role of ISO in all this is simply to adjust the brightness of the LCD playback and OOC jpg to the desired level.

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