D200 how to avoid over-exposure ?

Started May 26, 2006 | Discussions
Kaj E Veteran Member • Posts: 9,325
Re: D200 how to avoid over-exposure ?

I remember one post on this forum where the OP had done tests of the histograms vs. actual RAW highlight headroom and determined that the RAW image could well be overexposed by about 1/2 EV compared to where the normal contrast histogram indicated that the highlight (RGB) was maximally exposed.

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Kind regards
Kaj
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Kaj E Veteran Member • Posts: 9,325
Zone system

If you want to be really accurate with your exposure the zone system developed Ansel Adams comes in handy. Just remember that with digital and slides you typically expose for the highlights, not the shadows.

http://www.normankoren.com/zonesystem.html#Determining

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virtuamike Veteran Member • Posts: 3,569
Re: D200 how to avoid over-exposure ?

Yup, which is why you want to nail WB.

Kaj E wrote:

The important thing is not to blow the highlights in any channel
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Truman Prevatt
Truman Prevatt Veteran Member • Posts: 6,444
Re: D200 how to avoid over-exposure ?

For critical work I use a digital spot meter that I have calibrated to the D200. I meter the highlights I want texture and add four stops.

I then set the shutter and aperture to this setting in the manual. I shoot the shot and then retake it at + - one stop.

Unlike film you get the dynamic range you get so you must expose for the highlights.

Stefaan De Rore wrote:

When I shoot landscapes with a high dynamic range I get
over-exposed pictures more often then I like. I have been using
matrix metering and I shoot RAW with JPEG FINE.

Is there a way of getting the camera to avoid clipping highlights,
even when as a consequence the shadows would be to dark ?

I do not feel I can trust the after shots highlights indication of
the camera.
I get the impression that the after shot highlight indication only
applies to the in camera JPEG processing not to the RAW. I already
had cases where the JPEG was bad but the RAW was still OK and
correctable in NC by reducing the exposure.

Correct me if I am wrong but I think also the histogram shows
what's in the JPEG and not what is in the RAW.

So my first problem is to see if the picture is really over-exposed
before I can decide if an exposure compensation is necessary.

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Truman

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Mark53 Veteran Member • Posts: 6,583
In the scenario given...

Jim Fenton wrote:

Matrix metering averages and exposes based on a database of images
stored on the camera.

To properly expose, you must know how to utilize EV compensation
and to do that properly you need to understand and know how to
evaluate the luminosity of your scene / subject.
--

In his case, it's probably better to use center-weight or spot metering on the highlights to find the maximum exposure to avoid blowing the highlights. Matrix takes too many factors into consideration. Also, EV compensation is much more predictable when not using matrix, in fact, the user guide recommends not using exposure compensation in matrix mode (though we all do).

OP Stefaan De Rore Regular Member • Posts: 132
Re: Spot meter on highlights

tnielsen wrote:

Hi Stefaan

Let's for a moment assume we are talking B&W-photography
18% grey is the tone lightmeters are calibrated to "seing". What
this means is that if you point your camera towards a white piece
of paper covering the whole field of view, and let the light meter
decide on exposure, the resulting image will be 18% grey - sort of
medium grey. If you do the same with a piece of dark grey paper,
the same thing happens: The image will turn out 18% grey. The
lightmeter measures light reflected from the scene and has no
chance knowing whether the scene is dark and well-lit or light and
poorly lit. Does this make sense?

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

Now if you spotmeter from the brightest part of your scene, the
camera will set exposure as to make the highlights 18% grey. If you
overexpose by one step, highlights will by rendered "one step
lighter" than 18% grey .. and so on. On the D200 an overexposure of
2.7 steps will render highlights completely white - on the verge of
blowing. There is nothing physical about 2.7 .. this is just how
the sensor in D200 behaves .. on the D70 it was more like 2.3

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

At higher ISO-settings the dynamic range of the D200 decreases and
you reach the point of blowing highlights sooner.

I hope this made a bit more sense

It does, thank you for the information.

best regards
Thomas

OP Stefaan De Rore Regular Member • Posts: 132
Re: D200 how to avoid over-exposure ?

virtuamike wrote:

The highlight indicator is inaccurate if WB is off, which is why
it's crucial to nailing WB. Generally I've found that if it's blown
out on the LCD then it'll be blown out when I process the NEFs. And
regardless of what the indicators say in Capture, blown highlight
detail won't come back. It'll pull the tones down for highlight
recovery, but the detail is gone.

I experienced this too and I often see color alterations. When I could not recover in NC I supposed that some of the channels were blown.

If it's an issue of too much dynamic range to capture in your
scene, then bracket.

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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

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OP Stefaan De Rore Regular Member • Posts: 132
Re: Spot meter on highlights

Thanks a lot Thomas for the usefull information.
I am going to experiment a bit as soon as its stops raining.

Kind Regards,

Stefaan

Truman Prevatt
Truman Prevatt Veteran Member • Posts: 6,444
Re: Zone system

I think the zone system is more important for digital sensors than film. With digital sensors you get what you get - you have no latitude with development. Digital sensors are not forgiving with over exposure.

Kaj E wrote:

If you want to be really accurate with your exposure the zone
system developed Ansel Adams comes in handy. Just remember that
with digital and slides you typically expose for the highlights,
not the shadows.

http://www.normankoren.com/zonesystem.html#Determining

Kind regards
Kaj
http://www.pbase.com/kaj_e
WSSA member

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Truman

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Larry Lueck Senior Member • Posts: 1,258
Re: D200 how to avoid over-exposure ?

Can you download curves for the D200?
May help: http://home.earthlink.net/~ladlueck/Tone%20Curves.htm

Stefaan De Rore wrote:

Correct me if I am wrong but I think also the histogram shows
what's in the JPEG and not what is in the RAW.

So my first problem is to see if the picture is really over-exposed
before I can decide if an exposure compensation is necessary.

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