Do we still need a TC?

Started 11 months ago | Discussions thread
MightyMike
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Re: Do we still need a TC?
In reply to Alastair Norcross, 11 months ago

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?

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Alastair
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Not sure where you read F5.6 or faster cause thats total bunk and has been for a long time, I think early on some reviewers just assumed it was the same restrictions as one sees on a canon system but that has never been true. don't read reviews from uneducated reviewers .

Also no teleconverter for the Pentax system actually reports to the lens or body that there is a teleconverter.

Another point, I found that on all teleconverters that use screww drive there is a gear in the screw drive path that slows the focus speed by 1:2 or 1:2.5 regardless of the magnification factor. It is my opinion that this is deliberate to convince people to rather buy a more expensive longer lens than a TC. However I will be contacting some technicians tomorrow to see if the can give a legitimate reason for slowing the AF down before i post a full report on this in the forum. For Pentax those TC's that also allow SDM don't have a chip telling the lens to slow the motor down so there shouldn't be a technical reason to do so and that at the moment is my opinion. If its true that the gearing down is not necessary I'll work on converting my TC's to have no gearing and just be 1:1.

For the most part but not always a 1.4x TC will still focus most lenses fast and a 2x TC some lenses fast, but now that i know of the gearing down I can guarantee you that with the TC will never be as fast as without. that doesn't stop me from using my Sigma 1.4x EX DG on the Sigma 100-300mm F4.0 EX DG and Sigma 500mm F4.5 EX DG with great success and little difficulty.

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Mike from Canada
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