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| Pentax SLR Lens Discussion Discuss any Pentax K-mount, screwmount, or medium format SLR lens, as well as filters and attachments. |
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| 08-09-2008, 09:00 AM | #1 |
| Site Supporter Location: West Virginia Gallery Photos:
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Posts: 335 | Does anyone know................ ........why the correct Tamron 1.4 and the right Kenko 1.5 TCs support USM and others don't? I speculate that this is accidental in that they were both discontinued around or even prior to the intro of the newer PTX Da*s but would appreciate any technical insights into why these units are 'special'. Just wonderin'.............  |
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| 08-09-2008, 12:04 PM | #3 |
| Site Supporter Location: West Virginia Gallery Photos:
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Posts: 335 | Well, I have a Promaster 1.7 AF with the two insode contacts. It will actuate the USM but not achieve focus. I think some Kenkos have the contacts too, but will not work on USM. I have concluded it must be on the electronics, but have no idea why......... |
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