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03-27-2011, 03:34 PM   #1
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Sigma 1.4x TeleConverter EX DG

Hello,
I bought a new Teleconverter Sigma 1.4 DG for Pentax and am undergoing tests and discovered the following with their lens SIGMA 170-500 APO DG f5-6.3 & 50-500 f4-6.3 APO DG.
While it seems to work good with the lenses and the AF focusing quicklyand OK.
The problem if is problem it s that !
In Exif of the photos does not seem to be any increase in focal length, which should logically show thanks to the 1.4 Teleconverter Sigma at any focal length or in an automated candelabra handling!
Is problem o

03-27-2011, 05:56 PM   #2
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This has been a known issue for years

It is most critical for shake reduction as you don't get the correct focal length and on some cameras K10/20 specifically can cause exposure errors. These are usually permanent offsets at least for me with the 70-200/2.8
03-27-2011, 09:55 PM   #3
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For a teleconverter to compensate for the change in focal length and f-stop it require some electronics in the converter to interpret the data from the lens, modify the data, and then pass on the modified data to the camera body. The only teleconverter I am aware of that does this is the SMC Pentax-F 1.7x AF Adapter, which compensates for f-stop (as I recall it doesn't compensate for focal length, probably because it has just a KA-mount on the lens side, and was designed primarily to provide some AF ability to older, MF lenses on a film camera in an era before shake-reduction when focal length was a significant consideration).

I own three different non-Pentax brand PZ-AF (power zoom, autofocus) teleconverters and all of them just pass through all data unmodified to the body. I just turn off shake reduction since I figure it's performance will be inconsistent, and if it's important at the time I make a note for myself what photos I took with a teleconverter in place, since it won't otherwise get noted in the EXIF data.
03-30-2011, 04:42 AM   #4
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Thank you for your answer.
It Helps me to understand !
Thanks

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