Z1-P aperture readings through 2X Teleconverte

Hi all

When using my Pentax 2X teleconverter for the first time in a while I noticed some strange happenings on my Z1-p. When using a Sigma APO 300mm f4, it was possible to seelct a maximum aperture of f/1.2 (as indicated on the camera body display), although it should only be possible to obtain f/8. I have heard rumblings about the chips/electronics of Sigma lenses not always working properly with Pentax, hoever this lens has worked OK on my MZ-3 many times before. Also, when using a Pentax FA 50mm f/1.4 with the same (Pentax) teleconverter, I can select a maximum aperture of f/1.4 when I should only be able to get f/2.8.

Does anyone know what is going on? I gave the electrical contacts a quick wipe, and checked for any fouling/debris in the aperture arm and ring, but nothing obvious seems to be wrong or jammed.

All suggestions gratefuly received

Cheers

Matt

That does sound very strange, are the readings always correct without the converter?

If all is well on the MZ-3 then the problem must be with the Z1-P, are you sure that the converter is clicking fully into place?

Is it a manual or AF converter?

Sounds like an electrical problem (or electronics within the 2x itself).
The Z1 & Z1p don't have the mechanical finger to read aperture, so they read the lens information digitally.
Most of the contacts are used to indicate max & min apertures, and there's an extra connector that is for digital transfer of information. I would double check the contacts on either side of the 2x.

Does the Sigma works fine without the 2x on the Z1?

(Sigma apparently refuse to pay the royalty for the body-to-lens communication protocols, and choose to reverse engineer it. Seems they don't always get it right, especially when dealing with the nuances of older bodies )

Matt

Hi Kimbo, it's the A-2XS converter - manual focus only.

Hi Matt

The Z1-p and Sigma 300mm work fine together without the converter, and the problem isn't restricted to the sigma as it is apparent on the Pentax FA 50mm f/1.4 (which shows f/1.4, not f/2.8 as should be the case with a 2X converter) - unless the aperture indication relates to actual lens setting and not effective setting? I wouldn't have thought that would be the case, however, so I suspect the problem lies with the converter itself.

I'll recheck to make sure the converter is clicking into place properly. I'll let you know what I find.

Cheers
Matt

The aperture reading with a teleconvertor refers to the physical aperture setting in the lens, not the effective aperture. The camera doesn't "know" the teleconvertor is there: it just thinks it's suddenly got a couple of stops darker. So with your 50mm lens when the aperture reading says 1.4 that means the lens is wide open and the effective aperture is about 2.8.

As to the Sigma problem, your guess is as good as mine, although putting it down to Sigma is a fair bet. Teleconvertors (and extension rings) of different eras can have different numbers of electrical contacts despite being marked similarly (especially if they're non-Pentax). Is it possible it either has too many or too few contacts for the camera/lens combination?

Steve

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Not sure about that Steve, I don't have an A-series adapter but my F 50mm 1.7 / AF 1.7x adapter and Z1-P show what I would expect ie; f1.7 wide open without the converter and f2.8 with converter fitted!

Same result using an A-series 50mm 1.7

A-series adapters may differ but I'd be surprised if they do, particularly as Matt says it's ok on his MZ-3.