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05-16-2010, 03:21 PM   #1
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Pentax 1.7 AF adapter.. where to buy and will it work with FA 300mm?

I was wondering if anyone knows of where I can find the Pentax 1.7x AF adapter in either Japan or the United States?

I was also wondering how well it would work with the FA* 300/2.8 as far as data goes? Will the camera know that the adapter is there and will it adjust for it?

Thanks in advance. Best wishes,

-albert

05-16-2010, 03:31 PM   #2
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I see the Pentax 1.7X AFA on eBay once in a while. About a month or two ago, I saw a listing for a bunch of them, shipped from Japan. IIRC, they were listed at US$ 350 shipped each.

About data, the 1.7X AFA modifies the aperture data from the lens to reflect the actual aperture of the combo lens + AFA. For example, if the max. aperture of the lens itself is F/4, the camera will see F/6.8.

But the AFA blocks the focal length data. In fact, with the AFA + lens (any) attached, the body when turned on will ask you to enter the focal length.
05-16-2010, 04:56 PM   #3
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QuoteOriginally posted by SOldBear Quote
But the AFA blocks the focal length data. In fact, with the AFA + lens (any) attached, the body when turned on will ask you to enter the focal length.
That can be a bit of an annoyance but not a deal killer... Does it still allow the lens to AF or does it kill the lens AF in favor of the adapter AF?
05-16-2010, 11:20 PM   #4
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QuoteOriginally posted by AlbertSiegel Quote
...does it kill the lens AF in favor of the adapter AF?
The lens's AF is totally disconnected from the camera. In other words, the AFA takes over the AF.

The AFA performs AF by moving its optic elements. Thus its AF has a limited range. For example, if you leave the lens at infinity, the AFA can't focus at something at minimal focusing distance.

So you have to "rough" focus by manually focusing the lens, then half press the shutter release for the AFA's autofocus to take over. This sounds like a big hassle. But in practice, it becomes second nature and you can do it without thinking.

For the FA 300 you mention, you can use a Tamron 1.4X or even 2X TC. If you can find them, they are sure less costly than the Pentax 1.7X AFA.

05-17-2010, 01:34 PM   #5
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pentax should really make a teleconverter in production.
05-19-2010, 02:49 PM   #6
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I have this TC. Bought from a chinese user on Ebay, was shipped from Japan.

It works with my DA300mm F4 & 55-300mm (AF in good light).

It does not work with my Sigma 500mm F4.5.
05-19-2010, 09:39 PM   #7
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QuoteOriginally posted by AlbertSiegel Quote
I was also wondering how well it would work with the FA* 300/2.8 as far as data goes?
-albert
Works great with our FA* 300mm/4.5

If it doesn't work with that FA*/2.8 we could always talk about a trade
05-20-2010, 05:42 PM   #8
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I would add that it works wonders with the FA*300mm 4.5

on a fairly sunny day I barely notice the difference with the TC on other than it being a little more awkward to walk around and shoot.

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