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03-22-2010, 12:15 AM   #1
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Catch-in-focus with Sigma 500mm f4.5 & K-x

Does anyone know how to make this work? I have a manual lens which works OK but on the Sigma, switching to manual only affects the focus ring, it still auto-focussed unless the camera is switched to MF. Adding a TC does make it manual but the lens manual warns to switch the camera to MF to prevent damage to the camera motor.

03-22-2010, 12:28 AM   #2
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The traditional way of finessing this is to put a dab of metal foil or tape on the bottom contact (closest to six o'clock). Shorting these contacts does no harm.
03-22-2010, 12:36 AM   #3
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Do you short out 2 connections or one to the body of the camera?
03-22-2010, 09:43 AM   #4
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QuoteOriginally posted by PMunks Quote
Do you short out 2 connections or one to the body of the camera?
Just the one is all that's necessary. I'm fuzzy as to what all the connections do -- hopefully, someone with more expertise will jump in and inform us -- but apparently it's that last one that tells the camera if the lens is AF or not.

I've inadvertently shorted 3 or 4 contacts with aluminium foil between body and kit lens, and the camera couldn't get ID or focal length info -- SR asked me for the FL. Trap-focus worked anyway. I repositioned the foil to cover just the 6-o'clock contact, and trap-focus worked, with all other info automatically transferred.

Again, the shorting is non-destructive. I use a flanged adapter for some screwmount lenses, which adapter shorts out all the contacts, to no detriment. On M42 lenses with wide enough bases, I just put a strip of gummed metal tape on the lens base, then a non-flanged adapter, and several contacts are shorted. You can experiment with your Sigma, shorting one or more contacts, and see what happens. I may try that after I wake up. Gah, time to make some coffee...

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