Teleconverter magnification comparison. (5 imgs)

Started Aug 25, 2013 | Photos thread
KentG Veteran Member • Posts: 4,705
Re: Kent...

Well It still seems strange to me. While I do not have any of those particular lenses right now I have used Sigma TCs almost exclusively regardless of what brand of camera I was using at the time and have yet to have an issue with any of them not working. And it could very well be electronic. From my own experience I know that sometimes when newer cameras come out Sigma lenses do not work. This is an electronic issue usually caused by the camera company making a change that affects the "code responce" from the lens.  All EX and EX DG lenses and TCs have electronics that "intercepts" the code response sequence from the lens to the camera. This is done in many cases to cause the camera's AF drive to work at a slower rate if the F-ratio of the combo is close or at the F5.6 limit for that brand. Did not exist in the pre-EX era as they were all mechanical. However Sigma went from imbedded ROM chips (EX series) to flash memory (EX DG series). They don't update EX anymore, as the memory chips don't exist any longer.

As for the mechanical issue about not locking up that has me stumped as I have never seen a Sigma TC fail to do that on any lens regardless of brand that I used on a Pentax camera. But here is something to note, sort of a Twilight Zone thing. A Sigma optical product with a Sigma camera mount will do just that because they use a PKA mount that twists CCW instead of CW like the Pentax. All the way back to their first non-AF cameras, thru their AF ones to the current SD and DP line. Anyway skipping that if they do not lock up how can you know whether the electronic contacts are even lining up. If they don't the AF screwdrive will not work because the camera will not know a lens is attached. I mean I have a Tamron Pz-AF 1.4x that I never used because I only bought it to use or try to use with SDM lenses. I use a Sigma 1.4x EX TC exclusively on all my Pentax and 3rd party lenses, primarily on my K20D as I have not updated to a newer body (except the K-01).

Has to be something more to this. Sigma sold their TCs right thru the F and FA years and I never heard any complaints during those years when I was big on the old Pentax backed Pentax-Discuss forum.

K

 KentG's gear list:KentG's gear list
Pentax K-5 IIs Pentax K-S1 Pentax K-1 Pentax smc D-FA 50mm F2.8 Macro Pentax FA 150-450mm F4.5-5.6 +3 more
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