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02-19-2008, 10:16 AM   #1
Igilligan
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How does the Pentax tc focus with a MF lens

So I see every once in a while in the marketplace a AF Pentax TC that goes for +$400. It is said it can focus with the old MF lenses. You dial in close focus and the TC can fine focus the rest of the way.

How exactly does that work? Do the elements in the TC actually move slightly?

And do you get the focus indicator and beep like you do with a AF lens? Most of the old lenses I am trying to slowly collect are faster, with goodecent bokeh. I know the TC will affect the speed, but does it affect the bokeh too? It must, right?

What else makes this TC worth the 4-5 hundred dollars.
Thank you to the lens gurus who can help me with these questions.

02-19-2008, 11:00 AM   #2
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I have this TC. Personally, I think it is a little overrated. In fact, I like the Kenko 1.5x AF TC much more. But maybe I haven't tested the 1.7x AF adapter well enough.

Having said that: yes, the elements inside the 1.7x AF adapter move slightly when you press the shutter half-way. It's much like the IF (Internal Focusing) mechanism of some of the longer Pentax lenses. You also have the AF confirmation in the viewfinder.

And yes, it does affect the Bokeh. But it depends on the circumstances if it's bad or not...
02-19-2008, 11:47 AM   #3
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I have the 1.4 - expensive yes. Does it work, yes. Am I happy with it, yes.

The point is, not having to fork-out new money for new lenses with AF.
02-19-2008, 12:11 PM   #4
Igilligan
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Hey JC
Oh that makes sense... I dont know why, but I thought it was a 1.7x ... but at 1.4x it is not bad.. A 50mm would only end up at 70mm. That is much more usable than a 1.7 or 2.0x

Thanks, it is attractive as an AF for MF lenses....

02-19-2008, 12:17 PM   #5
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QuoteOriginally posted by Igilligan Quote
Hey JC
Oh that makes sense... I dont know why, but I thought it was a 1.7x ... but at 1.4x it is not bad.. A 50mm would only end up at 70mm. That is much more usable than a 1.7 or 2.0x

Thanks, it is attractive as an AF for MF lenses....
I think JC got his facts wrong. There is no 1.4x adapter that lets you autofocus MF lenses. He's probably mentioning the Sigma 1.4x EX AF teleconverter, a regular teleconverter for AF lenses.

Last edited by Asahiflex; 02-19-2008 at 12:25 PM.
02-19-2008, 01:14 PM   #6
Igilligan
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I am sorry I did not see the other thread...

Wow I never do the search right.... I dont know how I missed the other thread....
I just realized someone else posted this same question before me... My apologies to all and the moderators can remove this if they want.

thanks to those who answered.

Asahiflex I think you are right about the 1.4 tele that JC was discussing. I was asking about the pentax 1.7x that can auto focus MF lens. I actually have a tamron 1.4 AF that works well as a TC but obviously does not AF the MF lenses.

Jc, if you do have a 1.4 tc that can auto focus the old manual lenses I would be interested in hearing more about it.

Thanks again
02-20-2008, 07:12 AM   #7
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JC certainly did get MY facts wrong. I WAS referring to the 1.7x although I do have the other TCs referred to.

However, the point remains the SAME, one needs not purchase AF lenses and "throw" away the manual focusing ones.

As for the other thread, although similar to this one, the questions was HOW does it work.
02-20-2008, 07:29 AM   #8
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I recently aquired the 1.7 AF TC and have tested it a little. The instructions say you should only use it with MF lenses, and only with lenses with a maximum aperture of 2.8 or greater. It also says it should not be used, and will not work, for macro.

It works well. I used it on a 100mm A lens and it worked fine. It works by moving the internal elements of the TC. I also just played around with it a little, and it actually will work with an AF lens and it will also work with macro, but it's trickier of course, because macro focusing is kind of an art in itself anyway. Naturally works better at infinity focus. So it takes a while sometimes to get the auto-focus indicator to light. But so far, I'm pretty impressed with everything except the price.

Cheers

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