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06-22-2011, 03:49 PM   #1
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Tamron SP AF70-200mm F/2.8 with Pentax F 1.7 AF Adapter

I'm looking at this Tamron lens and since I have a Pentax F 1.7 AF Adapter would like to know if anyone has tried this combination. Reshearched several forums but nothing conclusive. Thanks,
Earl

06-22-2011, 08:55 PM   #2
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What conclusive results are you after, whether AF function fine or not, IQ degradation in image? I don't have your lens but the Pentax F 1.7x AFA works without any problems with SP 30A 80-200/2.8, and with some limitations with SP 19AH 70-210/3.5 (need fairly bright subjects to AF). IQ degradation is a fact of life when any TC is used but the F 1.7x AFA is probably the best of the lot.

Thanks,
06-22-2011, 09:03 PM   #3
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I don't think the Pentax-F 1.7 AFA has any problem with the Tamron SP AF70-200mm F/2.8. I use the AFA with my Pentax DA* 60-250mm F/4 all the time.
06-22-2011, 09:15 PM   #4
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QuoteOriginally posted by merengue Quote
I'm looking at this Tamron lens and since I have a Pentax F 1.7 AF Adapter would like to know if anyone has tried this combination. Reshearched several forums but nothing conclusive. Thanks,
Earl
There's not much the Pentax-F 1.7x AF adapter won't work with, since the AF is in that adapter, and it completely disables any AF that an attached lens has.

Keep in mind that if you don't own the Pentax-F 1.7x AF adapter already, you could save some money by buying a more common pass-through screw-drive AF teleconverter, since the Tamron is a screw-drive AF lens (it's one of the reasons I chose it over the Sigma 70-200mm f/2.8 HSM lens).

06-23-2011, 04:59 AM   #5
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Thanks for replies (see notes)

I thank everyone for their replies. This lens has an AF/MF ring switch but the Pentax mount version requires using both the lens and the camera switch. I don't know how this would work with the Pentax AF Adapter since the procedure is to first manually focus the lens to get close, and then auto focus. This could mean using the camera switch twice, which complicates matters. This is why I was looking for comments from someone who has used or tried to use this lens/adapter combination.

Earl
06-23-2011, 07:22 AM   #6
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QuoteOriginally posted by merengue Quote
I thank everyone for their replies. This lens has an AF/MF ring switch but the Pentax mount version requires using both the lens and the camera switch. I don't know how this would work with the Pentax AF Adapter since the procedure is to first manually focus the lens to get close, and then auto focus. This could mean using the camera switch twice, which complicates matters. This is why I was looking for comments from someone who has used or tried to use this lens/adapter combination.

Earl
I own the Tamron SP 70-200mm f/2.8 and three different Pz-AF teleconverters (i.e. they just pass through everything from body to lens). From reading about the Pentax-F 1.7x AF adapter I know how it works, so let me explain:

1) Screw-drive AF lenses like the Tamron have a focus clutch system where you pull the focus ring toward you and it engages the ring with the internal focus system allowing you to manually focus the lens. Push it forward, it mechanically disengages the ring, which reduces the mass the camera body needs to move (increasing AF speed compared to lenses with a constantly-engaged focus ring) and protecting the user from accidentally 'fighting' with the camera body AF motor.

2) The AF/MF switch on Pentax bodies, besides electronically altering body function so that a half-press of the shutter or press of the AF button doesn't activate the AF system, also mechanically retracts the screw drive and disengages the system from the lens, so that in the case where someone is manually focussing an AF lens, turning the focus ring, which turns the screw drive in the lens, doesn't also turn the screw drive entering the camera (if you ever accidentally manually focus an AF lens with the body set to AF you can feel the extra resistance as you turn the gears of the AF system inside the camera body, which isn't desirable).

3) The Pentax-F 1.7x AF adapter does not pass the screw drive through the adapter, i.e. an AF lens like the Tamron has it's screw drive AF shaft connected to nothing when it's attached to the Pentax-F 1.7x AF adapter. The camera body screw drive does connect to the adapter though, and the adapter has movable elements and can focus, but it cannot focus for the entire range of a given lens, so therefore if you want to use the Pentax-F 1.7x AF adapter and AF with a lens, you leave a lens like the Tamron SP 70-200mm f/2.8 with it's focus clutch in MF the whole time (because you need to get the lens somewhat close to the focus point manually first), leave the camera body in AF mode the whole time, and then half-press the camera shutter or press the AF button on the body to have the camera body move the Pentax-F 1.7x AF adapter's elements to attain focus.

So you don't change the AF/MF clutch on the lens or the AF/MF switch on the camera body after hooking it all up, there's no need to change it, or any possible harm that could come (i.e. without the Pentax-F 1.7x AF adapter in place, you wouldn't want to have the Tamron focus clutch in MF while the body is in AF because you could accidentally fight the AF motor if you grabbed the focus ring, but with the Pentax-F 1.7x AF adapter there is no longer any AF connection between a lens and the body, just the adapter to the body, and you can't manually focus the adapter, you can only manually focus the lens). You just set the focus clutch to MF on the lens, connect it to the adapter, connect the lens/adapter to the body, put the body in AF mode and leave it like that. Manually focus the Tamron to get close to the focus point then use the camera AF system to do the final AF (assuming there's enough light, which will be reduced because of the adapter).
06-23-2011, 10:50 AM   #7
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Thank you very much for taking out the time to research and then write such a detailed excellent description, which leaves nothing in the dark. I now feel confident that the Tamron will work with the Adapter.
Thanks again and best regards,
Earl
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