Algorithm used to calculate automatic settings in camera modes?

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Rob
Rob
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Algorithm used to calculate automatic settings in camera modes?
2 months ago

I was looking at the shutter settings my cameras picked in aperture priority mode (in conjunction with auto ISO), and that got me to wonder about the algorithm used to calculate the settings.

Now, assuming it's an Olympus E-M1, and I set the auto ISO limit quite high at 256,000, the lens is a 45mm MTF (90mm equivalent in 35mm), and aperture is set to f/1.8 (roughly f/3.6 in 35mm equivalent). When the camera looks at this setting, what type of calculation is it doing?

I would assume the first thing it tries to do is to get the ISO as low as possible to avoid noise. But I've noticed it would try and not get slower than 1/100, and I'm assuming this is because it is trying to avoid camera shake by keeping the shutter speed slightly faster than the focal length (which is 90mm). So now the shutter speed is overriding the need to lower the ISO, so the ISO will get bumped up to match the 1/100 speed. And if I want lower ISO, I can set it manually, which will then force the camera to set slower shutter speed in order to match the ISO.

But at the same time, the E-M1 has built-in image stabilization, so shouldn't that be taken into consideration as well? If not, then that means the camera disregards image stabilization when calculating automatic settings, and it's up to the user to set a shutter speed he thinks is slow enough to get away with, according to the subject he's shooting (moving or still subjects). In that case, it's better to use shutter priority or manual mode.

Am I pretty close in my assumptions about how cameras calculate and prioritize the automatic settings? Are there factors I overlooked and should consider? (For example, it might calculate the distance to the focal plane of the subject and take that into consideration?)

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Rob
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