Why Exposing to the Right (ETTR) is BAD!

Started Mar 30, 2013 | Discussions thread
apaflo Veteran Member • Posts: 3,854
Re: Why Exposing to the Right (ETTR) is BAD!

mike703 wrote:

schmegg wrote:

Could you explain why?  As far as I can see if you underexpose by three stops (by using ISO 800 instead of 6400, but with the same exposure settings) you are just telling the camera not to multiply the signal by a factor of 8. Instead you do it yourself afterwards in PP (whilst protecting highlights).  Why would this not work so well with a Canon?

Because Canon sensors have noisy readout when compared to the EXMOR based systems (which I'm guessing you were discussing). So, if you underexpose by three stops and then bring it back up in post, you will end up with a noisier image than you will if you simply use the 'metered' ISO.

Yes, that discussion did indeed centre precisely on the EXMOR sensors.  Thanks for the explanation.  Now I've learnt two useful things in as many hours, not bad for a bank holiday!

It should also be pointed out that even with Nikon cameras it has the same difference, except it isn't as large.

The exact effect depends on where in the ISO range this is done, because analog gain is used up to somewhere between ISO 1200 and 1600, and there is not a 1 to 1 ratio of ISO to change in SNR.  Above ISO 1600 there may be one of two different types of digital gain being used.  With either type there is a distinct 1:1 ratio for the changes, but with the latest camera models it appears there is a significant different from earlier methods for digital multiplication.  Previously it was post ADC, and yes that means there is no difference at all between what happens in the camera and what you do in post processing to brighten the image.

However, it appears that modern ADC's have a variable DC comparitor voltage to directly produce "digital multiplication".  That means the brightest level still has the same number of tone levels available (i.e., 8192 levels in the top fstop  of a 14-bit ADC). Generally that isn't something you'll see making any difference... unless you do anything at all in post processing that compresses or expands tonal levels (brightness, contrast, white balance, sharpening, saturation, etc etc).

Hence there is a difference with Nikon cameras, and while it isn't as dramatically bad as what we used to see 10 years ago, it is indeed one of those finer points that makes the difference between "good enough" and genuinely professional products.

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