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07-21-2017, 06:06 PM   #1
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Limitations of the ZX-50

So the one autofocus film camera I have is a ZX-50.

It's a plastic crippled K-AF mount.

Am I right in thinking that it is only usable (with in-camera metering) with A and later series lenses (No K,M or M42?).

07-21-2017, 08:36 PM   #2
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If you don't have it already, the manual is available for free download from...

Pentax Manuals

Limitations and workarounds are discussed on Dimitrov's K-mount Site...

Features and Operation of the crippled Kaf Mount


Steve
07-22-2017, 05:22 AM   #3
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Those two sources seem to contradict each other:

The mainual:
QuoteQuote:
The screw mount lens CANNOT be used to this camera because correct exposures will not be obtained

Dimitrov's K-mount Site:
QuoteQuote:
This allows perfect operation also in the following cases:

The selected aperture is indeed the widest possible,
The lens has a manually operating diaphragm,
The lens has a fixed aperture (for example, it is a mirror lens).

In all other cases, the body underexposes by as many f-stops as the difference between the currently selected f-stop and widest f-stop.
07-22-2017, 09:31 AM   #4
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QuoteOriginally posted by timw4mail Quote
Those two sources seem to contradict each other:
I clicked through on your "Lenses" link. You have several M42 lenses and the camera body at hand. Put the camera in Av mode and set the lens A/M slider to the M position and see if the stop-down metering makes sense. I would do an exposure series something like this:
  • Well-lit blank wall (preferably indirect natural light)
  • Establish reference exposure with your K-1 using a lens with the "A" contacts,* fixed ISO, Av mode, center-weighted metering, and f/5.6. record the shutter speed for reference
  • Set the ZX-50 to the same ISO as the K-1 using Av mode and mount your SMC Tak 55/1.8 with A/M switch in the M position
  • Starting at f/2, meter the blank wall and record the shutter speed
  • Repeat for f/2.8, f/4, f/5.6, f/8, f/11, and f/16 (full-stop increments)
The shutter speed at f/5.6 should be close to that from the K-1 and the rest of the recorded shutter speeds should be in one-stop increments (i.e. response should be linear).


Steve

* A hand-held meter or a different, known good, camera may also be used as a reference. Do not use stop-down (green button) metering on the K-1 as a reference.

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