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Using the K-Mount Adapter for Pentax Q

Aperture control revealed · 01-13-2013 · By PF Staff in Photographic Resources

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!

PF Staff's avatar
About the author: Various writers regularly contribute articles to the Pentax Forums homepage blog. More recent articles are published under each author's forum username. We hope you enjoy our guides and news coverage!

Tags: pentax q, k-mount, adapter, aperture

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Achromatter [Delete] Apr 6th, 2013 9:33PM

Is there a difference as to which aperture control one uses, the lens or the adapter? Is one better than the other?(maybe due to closeness to the sensor?)

And I guess I should have asked first, why is there a need for an aperture in the adapter in the first place, especially if the lens already has it's own aperture ring? Is it just mostly for lenses without an aperture ring?


outback traveller [Delete] Mar 28th, 2013 6:28AM

Does anyone know what is the diameter of the tripod foot sleeve that will fit this adapter?

Unsinkable II [Delete] Jan 14th, 2013 8:26PM

This is the reason I'll be getting a Q. This and the 06. :)

Adam [Delete] Jan 14th, 2013 3:13AM

@zany- same effect as the minimum selectable aperture

zany225 [Delete] Jan 14th, 2013 1:53AM

This might be a silly question. On the lens, there are 6 steps of changing aperture. But there are 8 steps on the converter. What will happen if set the lens at "A" setting and turn the ring on the converter to 7th or 8th step? damaging diaphragm or completely close diaphragm, maybe?

VisualDarkness [Delete] Jan 13th, 2013 11:45PM

When comparing the adapter with the ones other manufacturers put out it's not expensive at all, especially with a pretty advanced leaf-shutter. If it had AF and automation it would have to be around the double.

sledger [Delete] Jan 13th, 2013 9:22PM

If the adapter was under $100 I'd have bought one in a heartbeat. But at the current price, nope (same goes for the O-VF1) - get real PENTAX!.

Adam [Delete] Jan 13th, 2013 5:15PM

@enoeske: no, because the lens's aperture diaphragm is used regardless of which ring you use. Because the Q only uses the center of the image circle, however, shooting wide-open will generally not be a problem, or at least nowhere near as big of a problem as it is on DSLRs.

enoeske [Delete] Jan 13th, 2013 5:01PM

Is there any change in image quality when you use the lens' aperture ring to stop down vs leaving it wide open and using the adapter to stop down? Often lenses are pretty soft wide open and I wonder if stopping down the adapter will sharpen up the image like stopping the lens down does.

imaspy [Delete] Jan 13th, 2013 4:39PM

Really want to use some of my K mount lenses on my Q, but it's so hard to justify the adapter when it costs me more than the camera did :(

LaurenOE [Delete] Jan 13th, 2013 4:20PM

This adapter takes the Q into a whole different level! I love mine!

Pentaxosaurus [Delete] Jan 13th, 2013 4:17PM

I guess that with a pre-A lens (K, M) you should set the adapter ring to “L”
and use the aperture ring on the lens. The aperture lever on these lenses is
not guaranteed to work linearly, so the positions on the adapter ring don't
necessarily correspond to F stops.

Docrwm [Delete] Jan 13th, 2013 2:21PM

Very nice step-by-step. Thanks for the pointers.

Medium FormatPro [Delete] Jan 13th, 2013 12:27PM

This adapter is by far one of the best tools available for this type of camera. One has access to the full range of PK optics made over the last few decades. Also especially useful if one likes distance/telephoto photography - at a fraction of the cost compared to items like the (yet unreleased) Pentax 560 or Sigma 500.

If you have a Q or Q10; this might be ones most valued tools in the (gadget) bag.