What situations are best suited for spot metering?

Question

I have found myself using spot metering on several occasions in order to get the right exposure, such as sunsets and on bright days with a subject in the shade. What other situations are well suited for spot metering instead of the standard matrix mode?

Answer

Shooting the moon is a pretty good time to use it. :-)

Basically anytime the subject you actually want a clear photo of is drastically different in brightness compared to the rest of the scene.

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How do I use spot metering?

Question

What's the right way to use spot metering? Is it better to use in manual mode than one of the priority modes?

There are questions about when to use spot metering, but none that serve as a tutorial to describe how to use it.

Please address the issue of exposure compensation. I am under the impression that spot metering is hard to use in aperture priority because you can't (to my knowledge) over/under expose an image in these modes since the camera will adjust other variables to get the proper exposure. (So I need to meter off something that is gray-ish since I can't meter off something black and compensate?)

This question is motivated by another one that I asked here. It became clear that I didn't really know how to use spot metering, and @rfusca suggested I ask a separate question about this.

Answer

I wrote a tutorial about this very subject on my website. You can read it here.

To summarise, there are two advantages to using it in manual mode:

1. Once you've set your meter for the prevailing lighting conditions, you shouldn't need to worry about the exposure again (unless you need to change the aperture or shutter speed, or the lighting changes significantly)
2. Using manual mode allows you to move beyond the 2 stop range you get on most cameras with exposure compensation.

Learn the zones (see link); then find something in your image that you want to assign to a particular zone. Spot metering is the best way to isolate a small part of your image without any extraneous elements getting in the way of the metering. I now shoot almost exclusively with manual spot metering.

Of course there may be valid reasons why it's not appropriate to use manual mode - you may be shooting in rapidly varying lighting conditions, for example. But learning how to use spot metering in conjunction with manual mode will add another tool to your belt.

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Does spot/partial metering always assume 18%?

Question

I'm beginning to work on understanding and hopefully effectively using different metering modes in my photography. I have done some reading and understand the benefit of using spot and partial metering in portrait photography. I am using a Canon 500D for reference, but I imagine it would be the same for most DSLR cameras.

My question is this: When I set the camera to spot metering, find the location in the frame which is the "most important" and let the camera meter that spot, will the camera always set the exposure with the assumption that the location I metered has 18% luminance?

To this effect, if I'm shooting a portrait and focus on the forehead for example, I can assume the camera set the exposure as if it were neutral gray, and then increase the compensation for lighter skinned people, and decrease compensation for darker skinned people?

Answer

Yes, that's how it works.

This can be helpful when you want to ensure that some subjects are to be exposed correctly. For example, meter off a white shirt and open up 1.5-2 stops to ensure it's not blown out. Another classic example is a black leather jacket. Metering off it and then stopping down 1,5-2 stops will ensure it looks black without losing detail.

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