Just what is the correct exposure?

Just what is the correct exposure?

This is a vexed question that crops up frequently and can be the source of conflicting pieces of advice from all quarters. So, just to keep the fire burning, here is Professional Imagemaker's twopence.

The first thing that has to be said is that the correct exposure is the one which delivers, for the photographer, the optimum balance of colour and overall image density. This in itself can be a variable feast and an image situation may call for an adjustment, either global or selective to achieve the photographer's version of the most pleasing result. By this we mean that the photographer is at liberty to take the 'optimum' exposure and then bias it, typical examples being:
• A desire to show extra detail in a wedding dress might cause you to darken the dress – an exposure correction.
• You may prefer your Caucasian bride to look a little more tanned and so alter the colour temperature – a colour balance correction.

Such 'local' circumstances may not be of any use to a beginner who perhaps has been told by a mentoring panel that their exposures are off but has no clear idea of how to get things back on track. In this situation you need to achieve an optimum exposure before you start to make artistic adjustments. Too many images are too far beyond redemption at the start of the process to need to worry about subtleties of tweaking colour temperature by 100 degrees. There is a wealth of advice out there but much of it is myth, not the least of which is that Photoshop and RAW files can enable you to recover a situation later. Some of the advice centres on the use of a hand-held meter rather than the camera meter. In our experience a well-used camera meter will always outperform a badly used hand held one and a hand spot meter provides inexperienced hands endless ways of getting things hopelessly wrong!

The first big decision is to determine if you are going to expose for an accurate mid-tone grey or try to push your exposure histogram as far to the right as you dare, the so-called ETTR method (expose to the right). The latter is billed as being better because the bit depth is higher for the brighter parts of the image, halving with each successive stop darker. This is a popular misconception that is only partially true. Image density is a logarithmic, not linear, mathematical function and there are sound, science-based reasons why the ETTR method has some flaws (see 'The ETTR Myth' http://www.rags-int-inc.com/).

The thing that everybody agrees on is that over-exposure is bad for digital images and that beyond a certain point no amount of clever mouse clicking in Adobe RAW will recover your detail.


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