Of course, the first question is why would I wanted to buy a meter that costs as much as my camera body?
The quick answer is because in addition to using an external light meter to get the right exposure, you can also and, more importantly, use an external light meter to control the amount of light coming from your light sources. Light sources? You mean there’s more than one! You bet. If you’re shoot available light (non-flash) you can make a huge difference to the image quality by introducing light modifiers such as reflectors. An external light meter can make this a piece of cake.
If you’re shooting with the flash off camera, which you absolutely should be doing if you want to create three-dimensational images, a flash meter will prove itself invaluable.
Now, boys and girls, if you’re interested in HDR photography an external light meter will ensure you’re not guessing at your exposure range.
The instructor said to use the spot meter to measure the light on the brightest area of the photo (typically white clouds) and set your highest exposure at two stops below that exposure (set the camera to manual mode and change the shutter speeds and not the aperture which will change the depth of field which is not desirable when shoot HDR).
Why two stopes? Because your camera can handle a four to five stop differential in exposure and two stops down is well within the ability of the camera to capture the correct exposure.
Why not just shoot five or six images at different exposures?
First: It uses up a lot more space on the memory car;
Second: It takes longer to download;
Third: It takes longer to process; and,
Fourth: There is no appreciable benefit to the final image.
The Sekonic guys figure two or three images at two stops apart should suffice.
Now you can use the spot meter in your camera but a Sekonic L-758 (d or dr) will make the job easier and more accurate as it is a high-precision spot meter (which is essential if you’re contemplating using Ansel Adam’s Zone System when shooting black and white images).
Considering I already own an L-358 and an L-398A I still can see an L-758 in my future.
BTW if you come to any of my classes on shooting either available light or flash photography you’ll see I always use my Sekonic light meters. (Highly recommended.)