Understanding Metering Modes?

Alright, so I sent my camera in for repair (finally, after month of procrastination) to get the focusing screen fixed, RIGHT after I bought some new equipment for my camera. You can imagine how upset I am!

ANYWAY, I read this (http://en.wikipedia.o​rg/wiki/Metering_mode) page, and am still pretty confused about what difference the metering mode makes on a picture.

Lets say I shot a picture in evaluative mode, and then shot the same picture in spot metering mode, what would the difference be? I've never really dipped into this area of my camera, so I wouldn't really know..

Evaluative: takes data from all metering zones, goes through algorithm to guess composition, and gives an exposure
Center Weighted Average: ...what it sounds like. Averages the entire scene to neutral gray, giving extra weight to elements in the middle of the frame
Partial: Poor man's spot (extends beyond spot metering circle)
Spot: Gives an exposure so the portion of the scene in the spot metering circle comes out as neutral gray.

ALL MODES take the target and try to render them to 18% gray. The primary difference in the modes is simply the selective AREA measured. Evaluative tries to assess each of the zones and still come up with 18% gray. So all modes will be fooled if the primary subject is not 18% tonality, and will be fooled if the metered zones are especially bright or especially dark. If all modes were pointed at an 18% tonality wall, all modes would give the same exposure.

Evaluative mode does get fooled. While the chosen focus zone has highest priority, the adjacent zones can bias the exposure wrongly. This illustration demonstrates that...while the focus zone is on a true 18% gray target card, the adjacent sky screws up the reading so the 18% card is underexposed!

quadwing wrote in post #9658931
Alright, so I sent my camera in for repair (finally, after month of procrastination) to get the focusing screen fixed, RIGHT after I bought some new equipment for my camera. You can imagine how upset I am!

ANYWAY, I read this (http://en.wikipedia.o​rg/wiki/Metering_mode) page, and am still pretty confused about what difference the metering mode makes on a picture.

Lets say I shot a picture in evaluative mode, and then shot the same picture in spot metering mode, what would the difference be? I've never really dipped into this area of my camera, so I wouldn't really know..

Spot metering takes a sample from a much smaller area, so you can be very specific as to what you want to meter from. So if you want to meter off of the blue sky, you would point the metering circle at the sky, set your camera up (in the case of Av/Tv mode you would lock the exposure with the "*" button) then recompose and shoot without changing the settings again. This will better expose the sky but perhaps underexpose other elements in the frame. There's no getting by this whether you use evaluative or spot. It's not magic.

Keep in mind these modes are different ways to get to the same place. There is no magic bullet. The term "Correct Exposure" is somewhat subjective, but if you get to know your camera well enough, you'll be able to guesstimate rather well, even in evaluative.

Wilt wrote in post #9659374
ALL MODES take the target and try to render them to 18% gray. The primary difference in the modes is simply the selective AREA measured. Evaluative tries to assess each of the zones and still come up with 18% gray. So all modes will be fooled if the primary subject is not 18% tonality, and will be fooled if the metered zones are especially bright or especially dark. If all modes were pointed at an 18% tonality wall, all modes would give the same exposure.

Evaluative mode does get fooled. While the chosen focus zone has highest priority, the adjacent zones can bias the exposure wrongly. This illustration demonstrates that...while the focus zone is on a true 18% gray target card, the adjacent sky screws up the reading so the 18% card is underexposed!

It should have exposed the card this way (exposure set with Spot mode)

Oh, okay. So if I'm in a tricky lighting situation, where I'd most likely get a silhouette, I'd want to use Spot?

quadwing wrote in post #9659815
Oh, okay. So if I'm in a tricky lighting situation, where I'd most likely get a silhouette, I'd want to use Spot?

Spot may help you in tricky lighting situations, but you still need to decide what the correct exposure would be. Exposing for the foreground and having a blown out background or the reverse. You can't have it both ways unless you use fill flash or bracket the shot and merge the exposure in post or do HDR.

nicksan wrote in post #9659842
Spot may help you in tricky lighting situations, but you still need to decide what the correct exposure would be. Exposing for the foreground and having a blown out background or the reverse. You can't have it both ways unless you use fill flash or bracket the shot and merge the exposure in post or do HDR.

Ahh. Fill flash seems like the way to go, seeing as that if I did an HDR or merged the exposures, what would happen is that the subject (person) might be different another exposure, so that's why I'd prefer fill.

nicksan wrote in post #9659842
Spot may help you in tricky lighting situations, but you still need to decide what the correct exposure would be. Exposing for the foreground and having a blown out background or the reverse. You can't have it both ways unless you use fill flash or bracket the shot and merge the exposure in post or do HDR.

In other words, 'correct exposure' indicated by the meter for one item might not be 'optimal exposure' that strikes a compromise so that two different parts of the scene are both given an exposure in order to best capture detail in both areas.

In my example, the correct exposure for accurate rendiion of the gray card rendered the sky somewhat blown out and lacking in color. The evaluative mode exposure might have been a compromise for both the card and the sky.

https://photography-on-the.net/forum/showthre​ad.php?t=86497

https://photography-on-the.net/forum/showthre​ad.php?t=335569

quadwing wrote in post #9658931
Lets say I shot a picture in evaluative mode, and then shot the same picture in spot metering mode, what would the difference be?

Very often there will be NO difference. It will depend on the scene, and how the subjects are lit, but for average shooting, you will not see much difference in the exposure.


In a tricky situation, there is no "Magic" that will properly expose both dark areas and light areas. In those situations, exposure compensation, chimping, and Post Processing are more valuable to me than deciding between evaluative and center-weighting.

There is a great article in this months "Outdoor Photographer" about using the Zone System for metering in digital.