Using the K-Mount Adapter for Pentax Q

Aperture control revealed

By PF Staff in Articles and Tips on Jan 13, 2013

Let's take a brief look at the aperture control of the Pentax K-Mount to Q-mount adapter now that the adapter is finally available.

If you use it with a lens without an aperture ring or with a lens where the aperture ring can bet set to "A"  things are fairly straightforward. The aperture of the lens is simply controlled with the ring on the adapter:

  • The numeral "0" (also marked as "Open") leaves the lens diaphragm fully open (that means that it is at its largest aperture: F2.8 for the lens shown above)
  • The other positions stops the lens down from wide open by the number of stops indicated by the number on the ring. In the example above the lens is stopped down two stops, that would be to F5.6 (F2.8 -> 4 -> 5.6)
  • The ring has no click-stops so you can set values in-between as you see fit

If you use a lens with an aperture ring but without an "A" setting (aka a Pentax M or K lens) there is room for error. You basically must decide if you want to use the aperture ring to control the F-stop or if you want to use the ring on the adapter, and then leave the other ring in the correct position. This also goes for A type lenses of you move the aperture ring off of the "A" setting:

Adapter ring
controls F-stop
Aperture ring
on lens
controls F-stop

Fully open

(F 2.8)

Stopped down
Aperture ring MUST be set to the
smallest aperture (or "A" if available)
Adapter ring MUST be set to "L"

The adapter's aperture ring turns very smoothly, and it is stepless, so if you don't like being contained to full or 1/2 stop increments, it may be the better choice for you!

If you have both rings in some in-between position you really don't know which aperture you're getting, so either leave the aperture ring on the minimum aperture (22 in the example, or "A" if available) or the adapter ring on "L".

Stay tuned for an in-depth review of this adapter to learn even more about it!

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