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07-12-2011, 08:15 AM   #1
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Join Date: Jul 2010
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Posts: 328
Tamron 90 macro 52b Under expose KX, 100D OK !

I have a peculiar problem, using a Tamron 90mm 2.5 with a PK/A adapter
on my KX it will WAY underexpose on bright subjects to the point that the
pics are almost black. The exposure and speeds are always correct.
The same setup moved to the 100D does not give this problem at all, even though
the exposure settings show the same as the KX.
Have tried with 3 different PK/A mounts with the same results, the camera with
any of 6 other Tamron lenses does not give this problem !
Sometimes the first pic is good then the following ones are not, it seems to be that the
KX has a mechanical problem with this lens. Does it with or without the 2X extension.
In full manual though there is never a problem ?
I have stripped the lens and checked all of the mechanics and all is excellent.

Any Ideas ?

Thank You

07-12-2011, 12:41 PM   #2
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Join Date: Jan 2011
Location: Charleston, SC
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Posts: 350
This is the adaptall lens? If this is the case, the PK/A adapter is probably got crudded up contacts. I bet if you look at the maximum aperature the camera thinks the lens has on both cameras, you'll see two different answers. On the K100 it is probably right, and not right on the other. If that is the case, try scraping at the electrical contacts a bit or just try to shift the len mount slightly whlie mounted. I have this problem often with some of my PK/A adapters.

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