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09-17-2016, 04:18 PM   #1
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PDAF with stacked teleconverters

Hi Pentaxians,

I have two Kenko pz af 1.5x SHQ teleconverters and both work fine with 60-250 on K5.

The problem is when I stack them, where K5 can not focus using viewfinder (PDAF) unless the subject is far (~100 m at 250 mm). But using the Live View (CDAF) AF works well at any distance.

Is this normal?

Thanks.

09-17-2016, 04:39 PM   #2
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PDAF generally doesn't work with f/8, except with special sensors. Canon makes a big deal out of that in their marketing for the 5D Mark IV. It's not a matter of light. It's a matter of aperture doing I forget what but the sensors just don't work.

CDAF just moves the lens around until it finds a good spot so it doesn't care about anything except the amount of light.
09-17-2016, 05:11 PM   #3
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Yup, this is normal. Even without TC's, a F8 lens would really struggle to focus.

Adam
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