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03-28-2013, 01:16 AM   #1
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Q adaptor aperture accuracy with non A lenses?

We all know the saga of aperture movement differences between K and KA lenses,

The question I have is somewhat related.

With the K to Q adaptor, has any one measured exactly the change in exposure when using a K mount lens, on the Q ?

I suspect that each "stop" as indicated on the scale of the adaptor is no longer a linear progression like it would be with a KA lens.

03-28-2013, 01:34 AM   #2
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It will vary per lens, just like it does if you try to A convert such lenses for use on a modern K mount body.

Unlike that case though there's nothing to be gained compared to using the aperture ring on the lens, is there? Maybe more exact control than half stops. You can usually set the (lens) aperture ring between clicks if you're careful though.
03-28-2013, 01:41 AM   #3
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QuoteOriginally posted by drougge Quote
It will vary per lens, just like it does if you try to A convert such lenses for use on a modern K mount body.

Unlike that case though there's nothing to be gained compared to using the aperture ring on the lens, is there? Maybe more exact control than half stops. You can usually set the (lens) aperture ring between clicks if you're careful though.
I think the only thing to be gained is perhaps using the adaptor like an open closed ring on a preset.

Since all true Pentax K lenses have half stop increments except for the first and last which are full stops, and also considering the non linear movement in the K mechanism, there is nothing else to be gained with the aperture ring on the adaptor.

I was just wondering if any one had measured the linearity of each lens to see if it is really lens to lens variable or somewhat consistent
03-28-2013, 02:44 AM   #4
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QuoteOriginally posted by Lowell Goudge Quote
I think the only thing to be gained is perhaps using the adaptor like an open closed ring on a preset.
That will of course work.

QuoteOriginally posted by Lowell Goudge Quote
Since all true Pentax K lenses have half stop increments except for the first and last which are full stops, and also considering the non linear movement in the K mechanism, there is nothing else to be gained with the aperture ring on the adaptor.
You can always forget to move it to closed and be unable to close your lens down. Though that's probably not what most people consider a gain.

QuoteOriginally posted by Lowell Goudge Quote
I was just wondering if any one had measured the linearity of each lens to see if it is really lens to lens variable or somewhat consistent
I tried to make A lenses from several older lenses a few years ago, it never worked properly, but it certainly varied in the specifics.

Of course others should try it too, it's not proper science without independant verification.

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