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03-01-2010, 05:38 PM   #1
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focal length on camera using sigma 170-500 and tamron 1.4 af tele-converter

When I use the tamron 1.4 af tele-converter on the sigma 170-500, the camera will ask for the focal length. What Input focal length should I use on the camera? Is it better to just off sr?

03-01-2010, 07:06 PM   #2
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QuoteOriginally posted by jon pafford Quote
When I use the tamron 1.4 af tele-converter on the sigma 170-500, the camera will ask for the focal length. What Input focal length should I use on the camera? Is it better to just off sr?
Jon,

Unfortunately I have no answer to your dilemma but I sure would like to find out why it is asking that and what would be the focal length input.
I am sure, and I am hoping, that a guru on the matter will soon respond.

I am surprised to see that using a 1.4X TC will trigger a response from the camera asking to input focal length.

I use the Tamron 1.4X TC on a Tamron 70-200/2.8 and it doesn' task for that.

Also, using a 1.7X TC on a 300mm lens will do that too and I enter the resulting focal length which in my case would be 500mm.
That same lens, with a 1.4X TC, will not ask for focal length input.

Maybe that zoom of yours has such a wide focal range and that the "end" zoom is 500mm ...?

Can't wait to see the explanation.

JP
03-01-2010, 08:00 PM   #3
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how many pins are on the teleconverter? 6 or 7?

If the TC has only 6 pins, then it is not an AF TC because AF TCs have 7 pins and the 7th pin, (furthest away from the locking pin) transmits the focal length data to the body.

The AF TC needs focal length inoput because it does not transmit any focal length data from the lens. It only feeds focusing distance data from the TC focusing elements
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