@RobertTheFat wrote:
@TCampbell wrote:
Something to keep in mind is how the metering system works.
If you have a hand-held light meter, the light is falling directly on the meter. There is no lens. The meter reports the amount of light.
If you have a meter in a camera, then light has to pass through the lens before it reaches the meter. Since an f/4 lens reduces the light more than an f/2.8 lens... the meter doesn't really know how much light is actually in the environment unless it also knows how much the light is reduced as it passes through the lens.
For electronic lenses that interface with the camera, that information is reported and the camera can properly calculate the exposure. But for a completely manual lens with no electronic interface, the camera has no information about the lens, doesn't know the lens aperture, and can't realistically make any prediction about any exposure (not an accurate exposure anyway).
There are some manual lenses that are "chipped". Rokinon makes lots of lenses that are comletely manual, and often they make the same version in an edition that talks to the camera. If you use a completely manual (no communication of any kind) lens, then you would need to meter with an external light meter to get an accurate meter reading. If you have the chipped version (electronic interface) then it's still a manual lens, but at least the camera knows what's attached and the f-stop ... so it can provide a meter reading which is likely to be accurate.
Isn't metering with the "DOF Preview" button pressed an easier way to achieve the same effect as using an external meter?
I really used the example to explain why the camera meter is lost if it doesn't know what lens f-stop is used while the meter reading is being measured.
But "reflected" meters can never replace "incident" meters since the "reflected" meters depends on the reflectivity of the subject. If I meter two walls ... one black, the other white. Both are illuminated with a simple light bulb (assume same light bulb and same distance) the "black" wall will meter as darker than the "white" wall because black reflects less light than white ... even though the amount of light falling on the wall (from the light bulb) is technically the same.
DOF preview would still be subject to the reflectivity issue.
An "incident" meter doesn't measure the light after it reflects off a subject. The sensor on the meter is pointed back toward the light source. It measures how much light is reaching it from that light source (regardless of subject reflectivity).
I "own" a good quality incident meter (I have a Sekonic L-758) but I mostly just use the camera meter.
If I'm using manual flash, I use the Sekonic. It can "meter" flash (even manual flash -- the camera's built-in meter can't do that). It can also calculate flash-contribution percentage (relative to ambient light) -- which is something else the camera can't do -- not even a flagship camera has that ability.
Many incident meters also have the ability to meter "reflected" light. My meter has this ... but it's controlled to a 1° spot. This is something else you can't do with a camera. If you're shooting a landscape and you need to meter the reading for the white puffy clouds or the white snow-capped mountains... but you *also* need to meter the shadows the tree line, etc. the camera's meter in "spot" mode is still subject to the angle of view of the lens. That means you might be sampling a larger area than you want ... diluting the accuracy of the meter reading.
The other thing it can do is be profiled to your camera's true dynamic range and it can tell if you if a shot will exceed the dynamic range of the camera.
You can also meter multiple critical points in a scene and it will compute the recommended exposure that guarantees those critical points wont exceed the dynamic range.
Most of the time I just use the built-in meter on the camera. But there are certain types of photography where I prefer the incident meter. It's one of these things I think ever serious photography should probably "own" ... even though they only occasionally need to use it.
Tim Campbell
5D III, 5D IV, 60Da
