Spot Metering

[Hannah]

Hi,

Ameteur question here.

I understand what it means to spot meter, however, when you hear someone say that they metered a shot in 8-10 locations, how exactly does that work?

Does that mean they take an average of all of those readings or is there a way that our cameras can adjust exposure conpensation for different areas in one single shot?

Thanks in advance,

Hannah

[robertwgross]

I understand what it means to spot meter, however, when you hear someone say that they metered a shot in 8-10 locations, how exactly does that work?

Does that mean they take an average of all of those readings or is there a way that our cameras can adjust exposure conpensation for different areas in one single shot?


If you let the camera automatically meter in 8-10 places, then that would be the most common automatic exposure/metering mode that EOS cameras use. However, that may get good average results, but poor specific results as compared to what the photographer's trained eye might see. The photographer might meter at 8-10 places and then decide that he really needs something at about the compromise of places four and five (or anything else). This would be especially true if the scene has lots of dynamic range. If you just let the camera have its way with "dumb" metering, it may occasionally pick some dumb places that will yield an exposure mess.

---Bob Gross---

[DaveG]

Hi,

Ameteur question here.

I understand what it means to spot meter, however, when you hear someone say that they metered a shot in 8-10 locations, how exactly does that work?

Does that mean they take an average of all of those readings or is there a way that our cameras can adjust exposure conpensation for different areas in one single shot?

Thanks in advance,

Hannah

Spot metering was a very useful technique when I had control over the processing of the image as well as control over the exposure.

On a bright afternoon at noon there could be highlights many stops brighter than the shadows. I could use the spot meter to empirically measure those different points. The multiple spot exposure points would let me know what kind of an exposure range my shot might have in terms of contrast. Then, with that contrasty scene in mind, I could adjust my film development to compensate for the high contrast. This could be done with shorter development times ("exposure affects density, development affects contrast" to quote my favorite photography instructor) or by using a weaker developer, a low contrast developer (Selectol Soft anyone?) or a few other tricks.

The reverse can be true as well. If the lighting is very flat on a grey overcast day perhaps I would want to increase my development time to add contrast and once again using instruments - in this case a spot meter - will give me a more reliable result than by estimating.

But this is with film, and black and white film at that, and it is a very simple example of the Zone System.

With digital captures what do I plan on doing with this multiple exposure point information? If I read a spot meter and it tells me that THAT specific point is f8, and THAT one over there is f2.8, then yup, it's contrasty. So what do I do? I can shoot at 2.8, 4, 5.6, 8 or any point in between and they all will be right and they all will be wrong. I have no control at all over the "development" of the image so the contrast is going to stay right where it is.

Digital capture like slide film, has a very limited latitude especially on the overexposure side of things, so I probably should bias the exposure towards the f8 side of that example so that I don't blow out my highlights. My shadows in that example will be lost since in order to save the highlights I have to give them up. At the end of the day I get ONE combination of aperture and shutterspeed and that's all. It's important to remember that since no matter what the spot meter or any meter tells you, it can't be more than that with digital.

Now in the real world of digital photography what do you have in your camera? A meter, probably central spot averaging with probably some type of mosaic sensor pattern. This too will give you an estimate of the correct exposure in aperture and shutterspeed. It's sloppier than the spot meter so you would think that it wouldn't be as good. But along with that tool is your histogram. The camera's meter will get you close - as close as the spot meters varried opinion - and then you can fine tune the exposure after you view the histogram.

I watch the right side of the histogram to see if I'm getting any highlight clipping and I want to keep that to a minimum especially if I'm shooting with jpegs. From all accounts you will get less noise in the image if the "hill" the histogram makes is a little to the highlight side, but of course this is a little like playing chicken.

In any case you look at the histogram and you decide what to do. You can't help with the contrast, outside of adding fill light of some kind, which could be tricky if you aren't god and your subject is that mountain over there!

You could open up the exposure or close it down some. THAT'S ALL YOU CAN DO!!! So, once again, forget about a spot meter and it's eleven exposure points when you are using digital capture. Your camera's meter will get you very close and then you can use the histogram to make any changes you want.

[santa]

nobody really answered the question. Yes, some cameras, like the MKII can allow you to hit a button (the FEL button on the MKII) which will record a spot reading. Subsequent recomposing and FEL actuations will record and average the added spot meter readings. Each is shown in the columnar readout in the viewfinder on the right side. Cameras differ as to how they do mulitple spot metering. Canon's spot meter is something like 2.5 degrees (not sure) which is not very spotty for some folks. Other cameras only allow you to do a spot metering, period. No auto averaging of multiple readings.
It continues to have its' uses, and I use it myself occassionally, but frankly, the initial method you use to get your basic exposure is just not such a big thing now that people can view a histogram and adjust the exposure precisely. In a fast paced situation where chimping is not possible and lighting is extreme, spot metering really shines.

I understand what it means to spot meter, however, when you hear someone say that they metered a shot in 8-10 locations, how exactly does that work?

Does that mean they take an average of all of those readings or is there a way that our cameras can adjust exposure conpensation for different areas in one single shot?

[Mthorpe_Davies]

Unfortunately unless you own a 1 series camera you are S**** outta luck! Canon in there ultimate wisdom don't believe non pros need spot meters. Fantastic wonderful devices they are, I used it all the time on my last camera and miss it.