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Forum: Photographic Technique
07-06-2019, 10:24 AM
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I've always assumed that the spot meters in DSLRs will have a wider angle of view than the very precise Pentax Spotmeter, but I don't know the exact figures. For digital I shoot mostly with Takumars and I usually incident meter or follow Sunny 16, but I'll sometimes use a very simplified version of the zone system using the DSLR's built-in spot meter. Since digital cameras blow out to white in a horribly abrupt way, I usually concentrate on what I want to put into zones viii and ix and let everything else fall where it will. I'm usually so concerned about avoiding nasty blown highlights that I don't even bother to meter for anything below zone iv. I just cross my fingers and hope I can recover some detail from the raw file.
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Forum: Photographic Technique
04-03-2019, 01:31 AM
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Spot metering assumes that the area you are pointing it at has a tonal value similar to an 18% grey card and gives you the correct exposure for a grey card. If you are actually pointing at something lighter or darker than 18% grey, you'll need to adjust accordingly. The most sophisticated use of spot metering is the zone system, but that's too in depth to go into in detail here.
Centre weighted metering assumes that the tonal values around the centre and bottom of the frame will tend to average out to 18% grey, so it's only accurate if that's the case. Once again, if the actual scene averages out to lighter or darker than 18% grey you need to compensate -- snow being the classic case.
Matrix metering divides the scene up into zones, meters each zone separately, compares the results against a database of different patterns characteristic of different types of scenes, and tries to work out an exposure from that.
You've mentioned the specific case of metering for brightly lit parts of the frame, so one handy method is to do some tests to work out how many stops of overexposure compared to the meter reading your sensor can handle while still retaining detail. Brightly lit parts of clouds are a good test subject, so find a nice cloud and choose the brightest part of it that you still want to capture some detail in. Now spot meter that part of the cloud, and the spot meter will underexpose it by probably two or three stops because it assumes it's seeing 18% grey. Now increase the exposure by half stops or third stops, whichever you use, until you get to the last point where there is still detail in the cloud.
Let's say it turns out that your sensor can handle overexposing by three stops above the spot meter reading while still retaining detail -- now all you need to do is choose the brightest part of any scene that you want to keep detail in, spot meter that part of the scene (which will actually give you an underexposure reading because it's assuming 18% grey), then overexpose that spot meter reading by whatever amount your previous testing with the clouds decided on. You'll have detail in the brightest part of the scene that you want detail in, and all the other tonal values will be left to fall into place around that.
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