K-5 IIs, AF, and fast primes
I understand that only the center point of the K-5 IIs is sensitive to f/2.8, so when focusing such a lens, it is best to set to center spot and recompose as necessary to ensure accurate AF. But what about when lenses are faster than that? I've been using a K 50mm set to f/2.0 and when I can focus to a beep (AF assist), the result is great. Since it's an old lens, it only works in center focus mode. My questions are
1) Is AF assist accurate below 2.8? I assume the AF assist and AF engine are the same, but maybe not?
2) What happens with fast AF primes below f/2.8? Does the camera know this, stop them down to 2.8, and focus them, or does it leave them wide-open and try to focus, even though it knows the result may be inaccurate?
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