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03-08-2012, 06:58 AM   #1
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FA 50mm 1.4 - aperture not adjusting

Hi all,

This is my first post and I’m a relative newbie to photography so I must start by saying hi and apologising for my lack of understanding - sorry.

I have just purchased a Pentax FA 50mm F1.4 lens second hand and am trying to using it on my Samsung GX10 (I understand to be almost identical to the Pentax K10D). The lens looks in good conditions. The lens attaches fine, I've got it set to 'A' for auto aperture and the auto focus seems to be working. However, when using the camera in aperture priority mode and adjusting the aperture on the camera body I have noticed that the 'blades' of the lens (is that what you call then?) do no move. I checked when the lens was off the body that they moved by using the aperture ring - they do fine.

Am i missing something, do I need to adjust some settings somewhere? How would the camera body normally adjust the aperture?

Any help would be greatly appreciated as i don’t know where to start.

Thanks in advance - Phil

03-08-2012, 08:01 AM   #2
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The aperture blades don't stop down until you actually take the photo. The lens stays wide open while exposing to get a proper metering - it can figure out what the proper shutter speed/iso will be for the given F-stop you input without changing the actual aperture blades until the shutter is tripped.
03-08-2012, 08:11 AM   #3
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The aperture blades are always open for metering and focusing reasons. It would be difficult to adjust focus or frame your subject if the aperture is closed down. The viewfinder image is dark, the AF sensors don't get as much light they need to operate at their best and the long DOF makes it difficult to know exactly where the focus point is.
The camera actuates the aperture lever at the moment you take the picture, just before the shutter.

Last edited by bengibollen; 03-08-2012 at 08:12 AM. Reason: +spelling
03-08-2012, 08:15 AM   #4
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You can actually see them move if you set something like f/8, 1s and look into the lens as you press the button

03-08-2012, 08:59 AM   #5
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If the Samsung is similar to the K10D, set the aperture to something other than 1.4 - say f8. Then turn the on-off switch past the on position while looking through the viewfinder.
This should close the shutter blades so you can see the a depth of field preview. This action occurs during shooting. The resulting darker view is why it is left wide open so you can see clearly when composing.
They thought of everything, those engineers
03-08-2012, 09:59 AM   #6
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Thanks for all the responses - very quick. Hopefully, that's what it is - I'll have a look tonight when im home and let you know.

crewl1 - yes - that sounds the same as the GX10 - i've always wondered what that was for.

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