Why Exposing to the Right (ETTR) is BAD!

Started Mar 30, 2013 | Discussions thread
schmegg Veteran Member • Posts: 5,768
Re: Why Exposing to the Right (ETTR) is BAD!

Barrie Davis wrote:

schmegg wrote:

Barrie Davis wrote:

With a similarphotographic result.

NO. You are wrong.

Under standardised lighting conditions the affect at the sensor is precisely the same every time you expose it for 1/100th second @ f/8. That is "the exposure"... and it made in accordance with an effective ISO, even if not the ISO the camera happens to be set at... (see below)

The exposure does NOT change because the processing changes. In this regard ISO is just processing.

The sensor readout is not treated the same if the ISO setting is different. So exposing for ISO 200 with the camera set at ISO 400 is simply not the same as exposing at ISO 200.

It doesn't matter what the ISO is at the point of exposure because ISO only determines output afterwards. Output from the exposure is variable depending on how it's processed, and doesn't itself determine the exposure unless you allow it to in reading the meter. As we have seen, you can overexpose or underexpose from the meter, anytime, if you choose to.

But a delivered 1/100th @ f/8 is always 1/100th at f/8, and that will always be the same exposure no matter how it is arrived at...

The amount of light that is gather by the sensor is the same - yes.

What happens to it then, though, is not.

The photons are collected and generate a voltage. This voltage is then read from the pixels and amplified. The amount of amplification is dependant upon the ISO setting you have selected. The amplification may also introduce noise - and the significance an magnitude of this varies depending upon the particular sensor you are discussing.

So - even though the exposure is the same, the raw values recorded from it will vary depending upon both the ISO setting and the sensors ADC capabilities.

Your assertion that a shot exposed for ISO 200 but taken with the camera set at ISO 400 is "exactly" the same as the same shot taken with the camera set at ISO 200 is just plain wrong.

.... no matter how much underexposure is deliberately applied to nominally "higher" ISO settings, or how much overexposure has been added to nominally "lower" ISO settings. If the resultant exposure is 1/100th @ f/8, and that is what is delivered to the sensor by the shutter and diaphragm working together, then that is always the same, if the light strength is the same.

Yes. The number of photons striking the sensor is the same.

That is why 400-ISO shot with one stop's worth of overexposure for the sake of ETTR, is identical to 200-ISO shot straight. Please take note: Not just "similar in every way that matters"... but THE SAME, NO DIFFERENCE.

No. The resultant raw file is different.

Now, you can fart about with the histogram as much as takes your fancy after the event, but at the point of shooting they are THE SAME, NO DIFFERENCE, photographically identical.

No. Similar - and I'd go as far as to agree that in many circumstance the difference would be trivial and irrelevant - but, still, not the "same".

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