Do we still need a TC?

Started Nov 11, 2013 | Discussions thread
awaldram
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Re: Do we still need a TC?
In reply to Alastair Norcross, Nov 11, 2013

Alastair Norcross wrote:

So, just to be absolutely clear, these are using phase-detect AF, not live view AF? So everything I read about the PD AF system needing lenses with a maximum aperture of F5.6 or faster in reviews of the K5 and K5II was wrong? Or is this with a non-reporting TC? What is the AF speed like?

I don't think I've ever read a review stating f5.6 for Pentax cameras , as I say the only cameras this applies to is canon and even there it's a deliberate limit set in firmware of the converter.

I can't confirm what the k5ii will focus to but pretty obviously its greater than f5.6 else Bigmas , sigma super zoom etc would all be useless as there slower than that.

Maybe you or the reviewer are mis-understanding the specs.?

Pentax cameras upto and including the k5 have f5.6 sensors this means the base line extends to a max aperture of f5.6, So any lens faster cannot be more accurate than that from readings.

Later cameras have varying numbers of f2.8 sensors which means they have a wider baseline and can achieve higher accuracy reading from faster (2.8 and better) lens.

Neither of these directly reflect the max PD lens aperture that the camera can focus though it is related. the point 'blackout' occurs is the point the lens will no longer focus.

This point is dependent on sensor baseline + lens contrast +t stop + af module light losses.

As F stop goes up light requirements also rise to maintain decent AF speed, I can't tell you how fast AF is as indoor hand held at 1000mm is very sluggish but that is more related to my ability to hold target than the AF lock period.

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Alastair
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