I have fitted an old manual microscope objective mount to my Pentax K-3. It asks for the F-stop to proceed, which the lens cannot provide. I have tried all settings in the camera including manual focus and all options through the menu.

I imagine this problem is common to all older manual lenses.

  • Could it be that it's not asking for the f-stop (aperture) but for the focal length, in mm? That's only needed for SR (shake reduction), so either turn SR off or just enter any value. May 11 '20 at 5:00
  • Did you set "Using aperture ring" to "Enable"? May 11 '20 at 7:39
  • Here's more. Does your adapter short the electrical contacts (it should according to that post). May 11 '20 at 7:52

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