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05-20-2010, 08:34 PM   #1
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Tamron AF tele-converter with DA AF lens

I am trying out a Tamron 2x Pz-AF BBAR MC7 tele-converter on my K10D with the DA 18-55 kit lens. I set the camera in green full auto, the metering mode to multi-segment, and the AF in auto and single. It hunted a lot for focus, sometimes achieving proper focus and sometimes not, depending on the mass of the subject---a black cat, a wall, a flower pot, the side of the house. The light was not the best as it was later in the day.

Should this combination AF properly with my K10D and either the 18-55 kit lens or my DA55-300, if I set everything up correctly and have adequate light and a subject with adequate mass? I understand I'll sacrifice some light and f stops, which is ok. I primarily want to play with it with the 55-300 and I think manual focusing would probably work better in that situation anyway, but if the AF is just not going to work, I will return this converter and go with a manual focus converter for simplicity.

Any ideas or suggestions will be greatly appreciated.

05-20-2010, 09:11 PM   #2
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I would forget about using AF with that combo. It Might work ok at the 18mm end but when you go to 55mm, you're dealing with something like f11.2 (or something like that). Probably too dark for the K10d AF sensor to reliably pick up on anything.

05-20-2010, 10:06 PM   #3
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Moving this to the lens forum. I agree with Jeff, though- there's no point to it!

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05-21-2010, 05:59 AM   #4
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Thanks for the experienced replies. I "borrowed" it to try but it looks like my time and money could be better spent.

05-22-2010, 08:48 AM   #5
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Unfortunately the kit lens is slow to begin with. And a TC is really more useful at longer focal lengths. Even then AF will struggle ... unless it is a super bright day.
05-22-2010, 10:40 AM   #6
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Not only will AF struggle, but even if you get a manual-focus TC, there is basically close to zero chance that the IQ when combined with either of the lenses you mention will be as good as simly as simply cropping an image taken without a TC. That is, TC's on consumer zooms are almost always a completely waste of time and money on digital. On film, where cropping wasn't so trivially easy, the tradeoff may have been more worth it. On digital, though, only the faster/better lenses (mostly primes) will be worth using with TC's. The 55-300 might be kind of borderline in that department, but considering you lose a stop or two of light, AF won't work reliably, and SR won't be as effective because the focal length will be reported incorrectly, it's still going to be extremely iffy at best as to whether there is any benefit at all to using the TC.
05-22-2010, 11:04 AM   #7
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I have to agree with the above comments, particulalry Marc's spot on analysis.

I use this identical Tamron TC, with some of my primes and get some nice results. Here is a shot with it & the Pentax 165 f 2.8, Medium Format lens, for example:

05-22-2010, 12:02 PM   #8
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Now if that was with a 2x TC ... imagine the IQ without it ... it would be even more razor sharp.

05-22-2010, 12:39 PM   #9
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Thanks again for the additional comments. As I said, I just thought I would try it and ask for experienced suggestions, all of which I greatly appreciate.

I have a non-AF Tamron 2x that I have used some with Tamron Adaptall 80-210 zooms and it worked fine for the few shots I took, both with the K10D and the ME Super. I just viewed the digital shots on the computer though, and didn't really get into a full analysis of the quality, a task for which I am not qualified at my level of expertise. But for me just playing around in the yard shooting birds and the accompanying felines they looked fine, and I am sure I can improve on them as I gain experience.

I want more range, primarily with digital, for longer wildlife shots so I guess the best step is longer primes such as 300mm or 400mm without the teleconverters.

Thanks again. It is amazing what one can learn from the voice of experience.
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