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04-19-2011, 03:53 PM   #1
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M lenses focal length + teleconverters

When using non A lenses on a digital body one is asked to set the focal size in mm.

Does the camera do anything with that information other than use it to write the EXIF data to the pictures.

Questions 2 and three may be a mute point based on the answer to first question.

Second question: If one uses a non AF tele-converter do you input the lens size or the lens times 2x?

2X converter and an old zoom what do you input. My old zoom is an A so I assume it will pick it up as used. Have not really tested that but it works that way with the kit lens.

04-19-2011, 04:14 PM   #2
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When the camera asks for the focal length of the lens, it uses it for the Shake Reduction system. If you're using a 2X teleconverter you would enter the lens' focal length X2 (50mm X2= 100mm) With a 1.4 rear converter it is X1.4 (50mm x 1.4 = 70mm).
The "A" lenses still require you to input the focal length (at least I need to when I install my A50-1.7 onto my K10D). Also when using teleconverters you need to know that the aperture changes also. With a 2X it changes by 2 stops (smaller / higher number). With a 1.4X it is 1 stop and with a 1.7X it is 1 1/2 stops.
04-19-2011, 09:22 PM   #3
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Search for a post by m42man who had a bit of a scientific approach to the correct focal length that you 'should' input for zoom lenses.
04-20-2011, 04:46 PM   #4
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QuoteOriginally posted by calicojack Quote
The "A" lenses still require you to input the focal length (at least I need to when I install my A50-1.7 onto my K10D).

You are right. I wasn't thinking when I posted.

Thanks to all who replied.

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