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01-22-2011, 02:59 AM   #16
Stone G.'s Avatar

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I concur with stevebrot's remarks on Av metering issues: I have a Pentax K200D, several M42 Takumar lenses and a genuine Pentax M42 adapter --- and I just cannot get reliable meterings in Av mode.

Then I have two Tamron PK-M adapters of the Adaptall-2 type. No problems ever encountered with any of my six Adatall-2 lenses.

I also have 3 Tamron Adaptall-2 PK-A adapters. Two work flawlessly in all modes as per manual's desriptions. The third stubbornly refuses to allow seetings of aperture openings larger than f/4 with any Tamron lens. There surely are quality issues with the PK-A Adatall-2 design, as one can find quite a few references to here and at other sites.

One should also note that while PK-M adapters allow usage of all Tamron f-stops (normally to f/32), PK-A adapters only allow settings to f/22 only. Not that this is a major constraint in my opinion; all of my Tamrons perform better at larger apertures than f/32.

But the "safe starting point" to me certainly seems to be an Adaptall-2 PK-M adapter.

PS. -Just to add to the confusion: As said, my Takumars don't work with Av setting on my PK200D but my Tamron SP 350 mm f/5.6, Model 06 B (catadioptric mirror lens with fixed aperture) + PK-M adapter works excellent in Av-mode. And for Kitty's information: Being allowed to work in Av mode with MF lenses IS a great convenience. You do not have to worry about the Green Button (which I always tend to forget) but can concentrate entirely on the focusing.

B.R. / Stone G.

01-22-2011, 09:34 AM   #17
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The meter accuracy issue is highly dependent on shooting aperture and amount of room light. Apertures wider than f/4 generally underexpose. I have good luck at narrower apertures except for low light (outside meter's linearity range).


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