Can a Pentax FA lens aperture ring control aperture in Av mode on a Pentax DSLR?
Asked 5/16/2011
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I’m looking at a Pentax FA Limited lens for use on a Pentax DSLR. Since FA lenses have an aperture ring with an “A” position, can I set the aperture directly on the lens while using Av mode and let the camera choose shutter speed? Or does Av mode only work with the ring left on “A” and aperture set from the camera body? I’d prefer not to use full Manual mode.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
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To use aperture priority on Pentax dSLR with FA lens, you have to leave the aperture ring to "A" and select the aperture on body.
With aperture ring in A mode, the FA lens will behave just like a DA lens. You can use Av mode and set aperture on the body, shutter time will be calculated according to automatically measured exposure.
With aperture ring set on a specific aperture, the body does not know what you have set it to and would not be able to select shutter speed. By default, shutter will not work. You can enable using aperture ring in Custom Settings, but that will just enable using shutter - the lens will be used wide open regardless of the setting on aperture ring.
That's where the "crippled" part of the "crippled KAF2" mount on Pentax dSLR-s shows up - they do not have the mechanical linkage to read aperture settings from an aperture ring.
Originally by user4390. Source · Licensed CC BY-SA 4.0
user4390
15y ago
0
Generated from our catalog & community — verify before relying on it.
On Pentax DSLRs, Av mode works properly with an FA lens only when the aperture ring is left at A and the aperture is set from the camera body.
If you move the ring off A to a marked f-stop, the camera generally cannot use that setting for normal Av operation. On these bodies, the lens will not meter that way in Av; in practice it stays effectively wide open for exposure control.
If you enable use aperture ring in the camera’s custom settings, that only allows the shutter to fire with the ring off A. It does not give you normal aperture-priority operation from the lens ring.
To use the aperture ring itself, you typically need to use Manual mode with stop-down metering, usually by pressing the green button so the camera measures light and suggests/sets shutter speed. That workflow is for manual-aperture use, not standard Av mode.
So if you want aperture priority with an FA lens on a Pentax DSLR, leave the ring on A and control aperture with the body dials.
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