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11-29-2006, 10:34 PM   #1
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DOF Preview in K110D - lens stays stopped down when unmounted?

I have a quick question for a friend who's thinking about getting a K110D.

On Canons, when you press the DOF preview button, and the lens gets stopped down, when you twist off the lens while the button is down, the lens stays stopped down.

I know that Pentax lenses, when twisted off, stop all the way down. Does the same occur in Sigma, Tamron, or Tokina lenses in Sigma mount? Because the ones in Canon mount stay stopped at whatever aperture the DOF preview was set at when twisted off.

This is important for macro work with reverse wide-angle lenses that don't have a manual aperture adjustment ring.

11-30-2006, 04:12 PM   #2
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My Tamron 75-300 LD Macro lens (not the wide angle you were asking about) stays stopped down if pulled off the camera when DOF button is used. I own a DL and not a 110D

I think that function is built in to the lens itself and not the camera.

Maybe some others can reply with other specific 3rd party lenses.

Tim
12-01-2006, 08:27 AM   #3
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Yes, all A versin and later K mount lens should be stopped down off camera, if the aperture ring is in the A position
12-01-2006, 09:48 PM   #4
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Erm, lemme try to explain a little bit better.

Say a lens has a minimum aperture of f/22. You want it to be stopped down to f/8 when you reverse mount it. When you DOF preview at f/8 on a Tamron or a Sigma, and then twist the lens off, does it stay stopped down at f/8 or does it stop back down all the way to f/22?

12-01-2006, 10:22 PM   #5
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Stopping down

Most modern lenses for Pentax cameras have a spring loaded mechanism-I've got several Sigmas and Tokinas---applies to all.

They also, typically, have both an "A" stop and traditional "f/" stops (2.8,4,5.6,...). If the aperture ring is in the "A" position the lens stops down to its minimum size (f/22 or similar) because of the spring. If you twist the aperture ring to a particular numbered stop, then that's where the aperture goes.
12-02-2006, 11:04 PM   #6
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QuoteOriginally posted by fuzzybabybunny Quote
Erm, lemme try to explain a little bit better.

Say a lens has a minimum aperture of f/22. You want it to be stopped down to f/8 when you reverse mount it. When you DOF preview at f/8 on a Tamron or a Sigma, and then twist the lens off, does it stay stopped down at f/8 or does it stop back down all the way to f/22?
If you use a DA or FA-J lens which do not have aperture control rings, it will stop down to the minimum aperture. If you use an older K-mount lens such as K, M, F, or FA or a screw mount Takumar with auto/manual switch, the aperture will stay open to the aperture selected.
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