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Old Feb 24, 2007, 12:00 AM   #1
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Am seriously considering combining a 1.4 Tamron teleconverter with 70-300 Tamron and K10D.

Has anyone tried the Tamron 70-300 and 1.4 TC with Pentax digital SLRs?

Thanks:Ian Mc
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Old Feb 24, 2007, 3:26 AM   #2
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I use one with both the Sigma 70-300mm and a Sigma 18-50mm on my K10D

Making them 98-420mm and 25-70mm respectively.

It works quite well with no noticeable image distortion , and a just bit under 1 stop exposure impact. And dispite the warning of not using them on lens greater than 2.8... the 10D AF is just fine at the far end of both lenses which are both 5.6 at that point. And F4 and 3.5 at the wide end. Even in low (like post sunset) light

(The Tamron and Sigma 70-300mm's are very similar in specs and generally... So I would expect same functionality results with it)

And with the 10D's IS even 420mm (with crop factor 630mm effectively) is not any real problem, even free hand held, if you brace yourself well (Left elbow against chest, hand under lens and preferably hold breath) .

However the TC does not change the focal lenth reported to the IS system so it is still only reacting as it being 300mm/450mm, yet still good results. Its also doesn't change the EXIF FL reported.
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Old Feb 24, 2007, 9:26 AM   #3
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Ian - That's the exact combination I use with my K10D and istDl and I have been very pleased with the results. The two make an excellent pair.

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Old Feb 24, 2007, 10:07 AM   #4
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I use K100D with 50-200mm F4-5.6 and Tamron TC 1.4: as long as there is plenty of light it works fine. The auto focus noise is terrible thou: more like a power drill.
It scares kids, squirrels or birds. It makes people around you ask "what kind of camera is that?" :-)

Note that TC is to be used with 50mm and above lenses. I even use it with FA 50mm F1.4 (my cheap 70mm fast prime) and it does pretty good.
For $60 it is a great lens to own.
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Old Feb 24, 2007, 3:32 PM   #5
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Thank you Hayward, Ishino and Digital Addict.

Sounds like a good buy.

Hopefully will also work well on my Sigma 400 F5.6.

Time to go shopping !!!! LOL.

Cheers:Ian Mc
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Old Feb 24, 2007, 4:19 PM   #6
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Hi Ian. The Tamron does a good job as long as there's lots of light. You just have to remember your 5.6 will now be a 7.8 with it attached. Slower for sure, but useful in good light. In shady and poor lighting, it will do a lot of hunting for AF, and sometimes will not be very accurate. But on bright sunny days, shouldn't be a problem...cheers....Don
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Old Feb 24, 2007, 5:21 PM   #7
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Thanks Don.

That's very helpful.

Ian Mc
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Old Feb 25, 2007, 12:03 AM   #8
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thekman620 wrote:
Quote:
Hi Ian. The Tamron does a good job as long as there's lots of light. You just have to remember your 5.6 will now be a 7.8 with it attached.
Then again I think that is just Tamron covering their "we told you so" butts that you should have a 2.8 or better for it to function AF well/reliably/consistantly on cameras with so-so AF systems.

My SIGMA 70-300 on my original 300D Rebel FREQUENTLY got lost on its own....

But the advances in AF have been good..... Pentax K10D.... even in very low post sunset light almost never gets lost hunting (with the 1.4 TC) and IF it does comes right back releasing shutter and hitting it again where as the Rebel would stay for ever lost until you zoomed out some.... even with out a TC.

Its not the lens or TC particularly but the camera it is attached to and its AF system 300D Rebel was pretty horrid in low light even without a TC.... can't speak for the P K100D.... but the K10D rarely ceases to amaze me.... on only in very rare unusual exposure critical circumstance ever has it disappointed/failed... and then there is still manual... time permitting.
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Old Feb 25, 2007, 12:14 AM   #9
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thekman620 wrote:
Quote:
Hi Ian. The Tamron does a good job as long as there's lots of light. You just have to remember your 5.6 will now be a 7.8 with it attached. Slower for sure, but useful in good light. In shady and poor lighting, it will do a lot of hunting for AF
On previous cameras I agree but OP specifically said on a K10D.... something it does I have not seen others do it gets near focus in critical light.... it BABY steps incremenatally the AF.... maybe slower to finally lock but usually DOES... vs just full speed lauch off (overshoot) into never never land and never come back, some other cameras do.

At 300mm my SIGMA 70-300mm (again very similar to the same Tamron) is also 5.6 (effectively 7.8 ) but again with the T 1.4x and even post sunset low light... NO significant AF problems.

And in those situations the IS also greatly makes up for the reatively slow shutter speeds to FL, due to low light TC f/ impact.
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