Originally posted by lotech What is 'correct' exposure ?
It is what you decide it to be...assuming one has the knowledge and tools to make the decision.
To be quick and honest, nothing has really changed from working with film except that making a digital exposure exposes less flexible in regards to both dynamic range and tonal reproduction and/or detail capture of low values. One can still use a spot meter to place exposure and/or to measure the range of light in the frame. The difference is that the a range of light scan for digital capture is done with the intent to plumb the need to merge multiple exposures to retain shadow detail and tonality.
A gray card is still a very suitable substitute for an incident light measurement and on a Pentax dSLR should result in a nicely-centered histogram of a blank wall and/or reasonably exposed subjects when values within the frame are confusing to even our best matrix metering. FWIW, I carry both a gray card and an incident meter in my bag. I also have been known to use fill flash.
From the simple standpoint of correct metering, a centered histogram from a gray card is still "correct" exposure.
As noted above, it is probably easier to detect and critique "bad" or "wrong" exposure than to create a general rule or technique for "correct" exposure. To that end here are the bad hombres:
- Blown (clipped) highlights are unrecoverable since there are no available numbers to express the intensities that struck the sensor. The analogous case exists for all transparency films where there is truly nothing there. The common symptom is featureless snow or clouds.
- Blocked up (clipped) shadows are also unrecoverable since no data (true black) are no data. The most common symptom might be dark-gray textured fabric that renders as black. The analogous case for film photography is with negative films, though the "cliff" to black for a film negative is less severe in that an equivalent exposure that failed for digital may still be recoverable with many films at the same ISO.
- Muddied mid-to-low values that do not improve with combination pull/contrast boost. Inadequate data are inadequate data and while our software may do its best, there is little to work with in the lowest three stops of dynamic range.
- Poor color saturation and unintentionally "thin" rendering of high values.
- Blocked appearance of areas of saturated color despite detail being present in the subject. This is not true clipping, but happens none-the-less and is difficult to resolve in PP.
Working strategy? Work with the camera's meter while keeping ETTR in mind and remembering that either HDR or fill flash may be the only answers for some subjects.
Steve