How well do u trust ur camera's metering?

[Paddington]

Originally posted by ckiang


Actually, the grey card reflects 18% (or 13%, depending on which school you belong to) of the light falling on it. It not necessarily has to remain "grey". 18% of a bright sunlight is obviously different from 18% of indoor flourescent.

Thanks again for the helpful explanation. So that does mean a grey card is pretty useless in bright conditions right? That's my deduction. It's ok for me that the card doesn't have to remain grey. In fact, I can use a red card as long as I have a way to predermine it's equivalent to middle grey. What I'm more concerned is the limitations of the grey card.

From my experiment, the camera will always try to expose the card such that it becomes middle grey (which is what its metering system is programmed to do anway). In bright light, the card shimmers or glows (whiter in other words) and loses its "greyness". The camera, in turn, tries to bring it back to middle grey. The overall result though, is that I get underexposure. Cos, even if you don't do this simple test yourself, you will know that the card should be of a paler grey or brighter, not middle grey. In other words, the grey card is no longer accurate and becomes useless in helping one get a correct exposure. Please check my explanation as I hope to make sense and get it right.

The next question I have is: how will you know what is the limit of light shining on it that the grey card can hold before it becomes inaccurate?

 

[ckiang]

Originally posted by erwinx
agree with Ckiang. Bracket Bracket Bracket. (and then find out the Nikon matrix gives the right exposure most of the time ) Still, with 3 bracketed exposures, you can make the image even more 'perfect' by doing a 'digital ND grad'.

Nikon 3D Matrix is accurate 99% of the time. About the only time it's inaccurate for me is when there's backlight, or when shooting night-scene type photos.

Regards
CK

 

[Red Dawn]

Hi

I have also found metering my own hand pretty reliable.

Btw just because u use a grey card doesn't mean you can just take the meter values as is. That's a myth many believe about using grey cards -the cards may be calibrated to 18% grey, but your camera's meter is ACTUALLY calibrated to 13%.

Yup that's right. Manufacturers have taken to speaking of 18% as a convenient measure. (Though this really has to be tested on different cameras)

I think the ANSI standard is 13% (read that off somewhere).

Which means your grey card is lighter than wat the camera thinks it should be, and the meter will try to force it to 13% grey, thus underexposing the scene if u feed the values directly into the camera.

Further proof of this comes in the instruction I received with my Kodak Grey Cards. It says.....

Meter Readings of the grey card should be adjusted as follows:

- For subjects of normal reflectance increase the indicated exposure by 1/2 stops

- For light subjects use the indicated exposure; for very light subjects decrease exposure by 1/2 stop

- If the subject is dark to very dark increase the indicated exposure by 1 to 1-1/2 stops

Note that these are moderate exposure adjustments compared with the large errors that may result from making reflected-light exposure-meter readings directly from very light or very dark scenes

 

[Red Dawn]

Originally posted by Paddington


Thanks again for the helpful explanation. So that does mean a grey card is pretty useless in bright conditions right? That's my deduction. It's ok for me that the card doesn't have to remain grey. In fact, I can use a red card as long as I have a way to predermine it's equivalent to middle grey. What I'm more concerned is the limitations of the grey card.

[snipped]

The next question I have is: how will you know what is the limit of light shining on it that the grey card can hold before it becomes inaccurate?

Again, if u read the instruction that comes with the grey cards...........

....................be sure the grey card is illuminated by the same light as the subject you are photographing.

Position the grey card as described below so that there are no shadows on it, no brightly colored objects reflecting light on it, and no glaring (specular) reflections on the card itself

there are a few diagrams illustrating correct use of the card which unfortunately i can't reproduce here.....

 

[tsdh]

Originally posted by Red Dawn
Btw just because u use a grey card doesn't mean you can just take the meter values as is. That's a myth many believe about using grey cards -the cards may be calibrated to 18% grey, but your camera's meter is ACTUALLY calibrated to 13%.

Yup that's right. Manufacturers have taken to speaking of 18% as a convenient measure. (Though this really has to be tested on different cameras)

I think the ANSI standard is 13% (read that off somewhere).

Maybe not the ANSI standard, but the 13% grey has a point.
This excerpt was quoted from page 137 of National Geographic Photography Field Guide :

"Scientific studies now indicate that an average scene actually reflects 13 percent (not 18 percent) of the light that falls on it. For the sake of consistency, gray cards have continued to be 18 percent gray, as is the one in this book. When using any 18 percent gray card for substitute metering, increase exposure by a half stop (+0.5 compensation factor) for most subjects, as Kodak recommends. If the subject is very light--a snow-covered landscape, for example-- decrease exposure instead, by a half stop (-0.5 compensation factor) from the gray card reading. This will help maintain detail and texture."

 

[Paddington]

Originally posted by Red Dawn


Again, if u read the instruction that comes with the grey cards...........

there are a few diagrams illustrating correct use of the card which unfortunately i can't reproduce here.....

Ahh...specular reflections... so that explains. Need to check my Kodak guide again. :embrass:

But I'm sure I placed the card in the exact same lighting as the subject. I suppose in this case (very bright day) using a grey card is useless. The card is exposed to a middle grey as if it was an overcast condition while my subject is severely underexposed. But surprisingly, even the external light meter I used didn't give me an accurate reading... I still can't understand this part.