Our camera's metering system is TTL .... Through The Lens. It takes a meter-reading of the light that is coming through the lens. Poorly made lenses have a lot-of light reduction. In severe cases, such as the kit-lenses, the optical viewfinder even looks dim! Where with PRO lenses, the viewfinder is very bright, much brighter than our naked eyesight! Well, the light meter, no matter what brand or model, the light meter doesn't know how much light is reaching the sensor. It doesn't know if you've got a circular polarizing filter on the lens that is reducing the light by -3 EV. It doesn't now if you've got a ND filter on your lens. All the light meter does is give you a very, very accurate reading of the light that's actually there. It is your job to compensate for the lens and any filters that you might be using.
I know that you're thinking this is too much hassle. But it's simple to do. Using a incident light meter is much, much more ACCURATE than even the very best camera. Now that I'm past the learning, I am sold on light meters!
To calibrate the meter, you merely take a reading with the light meter, set the camera to that value and take a picture of the exposure disk or any 18% gray card or cloth. Then you look at the histogram of that image, and adjust the light meter or camera till the spike is centered in the middle-of the histogram. (18% gray is dead-center of our histogram. If the spike is not centered, the exposure is off). I find it EASIER to calibrate the light meter so that I don't have to fuss with the camera's exposure settings as I switch from "M" manual-exposure to "A" aperture-priority mode (which I also use. You cannot use a light meter for distant objects that you cannot walk up to and take a meter reading of). MOST of my photography is of people. (still life portraits in their every day atmosphere. Whether I use ambient lighting or supplement it with flash,
the light meter is the most accurate way of getting the exposure correct! And that's true no matter what brand of camera you are using. Light meters are by far more accurate than a camera!)
Once the meter is calibrated to your lens, you don't have to recalibrate it. As long as all of your lenses are pretty close, or if you mainly use one lens for all of your portrait or still life photography, you don't need to recalibrate. And if you do have lenses that are different, just remember the setting you used and quickly set it to that value for that lens! Our PRO lenses are close enough that the same setting works for either lens.
I was shocked to see how much of a DIFFERENCE that a light meter makes on an image! Check out Sekonic's info, which isn't merely a selling point, but quite frankly, the TRUTH! (You'll probably have to highlight, copy and paste the link into your browser's url www address bar as the links might-not work).
Sekonic Classroom: Metering Techniques
As far as whether one can "fix it" later in software, here's a very informative guide I personally found interesting:
http://www.sekonic.com/images/files/...rkTogether.pdf
*** Pay special attention to the part on the histogram of the "fixed" RAW file. Even though the image appeared to be fixed, the correctly exposed histogram looks completely different than the histogram of the "fixed" image!!! I am CONVINCED from that illustration that we cannot "fix" it later. A digital image just doesn't have as much dynamic range as film, and film does not anywhere near as much dynamic range as our eyesight! Therefore, if a digital image doesn't have anywhere near the dynamic range of our eyesight, then any exposure-error means that we've lost what little bit-of dynamic range that our camera has! Therefore, its all the more IMPORTANT to get he exposure CORRECT when we take it! Agree?
By the way, we use a D300, and never had any exposure problems with any of our lenses until we bought the 18-200mm "kit" lens. As long as the lens is wide-open, the exposure is fine! (Or at least acceptable). However, it works "fine" only when the lens is wide-open. We've had nothing but exposure-trouble with the 18-200mm lens. GREAT image stabilization, but beyond that, we've had too much exposure-trouble with this lens. And it causes the same exposure problems with other Nikon cameras! So from what we've found, there's something crazy about this lens (or at least ours). The D300 has had no exposure problems for us with other lenses. Only that 18-200mm kit lens.
We all have different levels of expectations. (Which is fine! We're all got different expectations!) If close-enough is good enough for you and your exposures, then I'm sure you're happy with your images. But if you want the best-possible image and details, then like me, you'll want a light meter!
