Onboard metering on the D70

[Blagsta]

OK, that's what it's doing.

But why?

Considering that most pics look better with something close to white in them, and the digital camera has a histogram, "knows" where the right-hand part of the histogram, and does all sorts of other clever things, why doesn't it do your exposure compensation job for you and whack the histogram over to the right for you automatically?

Because the camera doesn't know what its looking at. It only knows that most scenes look good at average of mid grey. It can't discriminate between scenes.

 

[alef]

The problem is that the light at the camera can be quite different to the light where the lens is pointing. A handheld lightmeter gives you perfect settings because you hold it directly in front of your subject. But for anything far away or out of reach you have no way of measuring the light that is there.

Instead the spot/matrix/whatever meter has to measure the light reflecting off the objects rather than the light itself -- a very big difference. Objects reflect light differently based on their colour (in fact that is what creates colour). So the only thing that can be done is to assume that everything should balance out to this magic 18% grey. I suppose we should try to remember what that shade looks like and always aim the spot metering directly at something in the picture that matches.

But on the whole I'm happy with cameras set to Auto or Aperature priority and then vaguely mess about if I'm snapping snow or dark silhouettes.

 

[Paul Russell]

Yes, but most scenes look good with a white point that is white, not grey, as well.

It only knows that most scenes look good at average of mid grey.

 

[Robster970]

mid tone grey = 18% reflectivity

camera likes mid tone and 18% reflectivity

white is 36% and black is about 9%

white bounces twice as much light into the lens as mid tone grey. therefore camera exposes 1 stop under. to get proper exposure you need to dial in +1 ev

black bounces in half as much light as grey. therefore camera exposes 1 stop over. therefore to get proper exposure you need to dial in -1 ev

camera thinks everything should be 18% reflectivity. the world just isn't like that as we know.

 

[Paul Russell]

camera thinks everything should be 18% reflectivity. the world just isn't like that as we know.

Is there someone I can complain to about this?

The Daily Mail?

 

[Robster970]

Is there someone I can complain to about this?

The Daily Mail?

I'd try your local MP first. The Mail will just twist it into something like

18% of Cameras admit to taking Drugs

 

[camouflage]

Almost, you obviously need to give increased exposure here though rather than 'negative' so as to lighten it.

So if the image is too dark, step up abit (positive) if the image is too light, step down abit (negative).

Yeah, you'd think it's obvious, I've only just learnt that you don't use a camera by bashing the subject with it untill the indentations in the casing form an image.

 

[Hocus Eye.]

Robster

While the mid grey to which light meters are calibrated is 18% the tone at 36% will not be white, just another grey that is twice as light. Similarly a 9% reflectance tone will not be black but just a grey twice as dark as the original grey.

White light can be up to 100% reflectance. Similarly black can be 0% i.e. no light at all.

For practical purposes a camera sensor or film can record a range of tones up to a maximum of about 8 stops that is a ratio of 128 to 1. If you expose for a mid grey tone in the subject you should be able to record the white end and the black end equally. If you over expose by 1 stop then you will lose detail at the white end and also risk a lack of contrast in the blacks. If you underexpose by one stop then you will lose detail in the blacks and risk losing a pure white in your image.