D200 how to avoid over-exposure ?

Started May 26, 2006 | Discussions thread
tnielsen Regular Member • Posts: 372
Re: Spot meter on highlights

It does make sense. Just wondering why they call it 18% gray but I
read somewhere else that this is the percentage of reflection on a gray
card

Exactly .. and a grey tone which the human eye percieve as being midway between black and white

If you say 2.7 renders highlights completely white does this apply to the
JPEG or the RAW ?

This applies to the jpeg. If you shoot raw you will still get blown highlights around +2.7 (that might vary from one converter to another) but in addition to that you have somewhere around +0.6 steps worth of highlight to recover (by lowering the exposure slider). So if you really want to push it you could shoot raw, dial in an exposure compensation of +3.3 and measure for highlights, and in postprocessing lower exposure to recover highlights. By this point most of the image will look completely blown on the camera lcd. There are a few catches though:

First: The exposure meter in the camera sees only Black&White, which means that the exposure-reading is averaged across all three colour channels. Thus it may very well happen that while you overexpose by 2.7 over the averaged reading, one of the color channels goes beyond blowing. This often happens photographing red flowers.

Second: When you recover highlights in RAW there is no guarantee that all color information is retained and you may end up with either strange color casts or completely grey highlights.

I recommend that you try playing around with this and find an optimum setting of overexposure. I mentioned overexposure by +2.7 / 3.3 (raw) and this should be a very safe level. Actually you should be able to go higher than that. If you consult Phil's dynamic range test in his D200 review :

http://www.dpreview.com/reviews/nikond200/page22.asp

the real limits are closer to 3.3/4.0
(the point where the curves reaches the top of the diagramme)

All this can be taken to a lot of different levels. Just as an overexposure of 2.7 always renders completely white, an overexposure by say +1 or an underexposure of -1.6 (and so on) always renders the same lightness. Now with practice you would find some key tones. F.eks. "Tanned skin in sunlight shows a lightness corresponding to an overexposure of +1.3" .. or "Green grass in shadow corresponds to an underexposure of -2" In order to get the right exposure on these key items, you could dial in the right exposure compensation and spot meter. The above numbers are just examples.

In Ansel Adams zone system, which was developed with analogue photography in mind, he devides the tonal range from black to white into "zones", where zone 5 correspond to 18% grey, zone 4 to an underexposure of -1, zone 6 to an overexposure by +1 .. and so on. Exposing is now the task of "putting" different parts of the scene into different zones. Taken to the extreme the zone system is a whole new way of thinking, but one can take a lot of useful parts of the system and adabt it to digital photography in a less nerdish and practical manner.

best regards
Thomas

 tnielsen's gear list:tnielsen's gear list
Nikon D800 Sigma 150-600mm F5-6.3 DG OS HSM | S +9 more
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