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03-11-2007, 06:12 AM   #1
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aperture not opening at 50mm

I just bought a 16-45 f4.and a K10d When I have dialled in f4 and zooming back from 16mm to 50mm the aperture sometimes does not go back to full open. If I zoom a little back and forth, I can see the diagram pops out to full open. I tok exposures with the same shutter and aperture in manual mode, and yes the pictures was darker when this happend. What can this be?
Has any of you experienced the same thing?

I am worriyng about the situation might worsen.

Cato

03-11-2007, 08:14 AM   #2
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I find myself wondering how you zoom to 50mm with a 16-45 lens.
03-11-2007, 08:55 AM   #3
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You are more than likely not set on aperture priority. Tv may show exactly that kind of behavior while zooming. If you wish the aperture to remain constant, Av is the mode to use.
03-11-2007, 12:24 PM   #4
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It is of course from 16mm to 45, but the problem is there independent of av setting or not. I can see the blades are not getting into position when I look into the lens.

03-11-2007, 12:41 PM   #5
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QuoteOriginally posted by chals Quote
It is of course from 16mm to 45, but the problem is there independent of av setting or not. I can see the blades are not getting into position when I look into the lens.
Tried remounting the lens or a different lens to compare? I'm looking at the end of one of my lenses right now - the long metal piece that controls the aperture opening, is it obstructed in any way by foreign material?
03-11-2007, 04:07 PM   #6
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if your using an AF lens, the aperture blades will not move unless you do DOF preview. regardless of what you set on the camera, unless you take it out of the "a" position.

only way you'll really see it is if you take a pic of yourself, then you'll see the blades move....
03-11-2007, 04:20 PM   #7
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QuoteOriginally posted by -=JoN=- Quote
if your using an AF lens, the aperture blades will not move unless you do DOF preview. regardless of what you set on the camera, unless you take it out of the "a" position.

only way you'll really see it is if you take a pic of yourself, then you'll see the blades move....

It is the other way around, I can see the blades in a not fully open position, even thogh the aperture i set on 4.0. when the picture is taken the blades does not open to 4 but stay at 2.8 and the picture get underexposed.
03-11-2007, 04:22 PM   #8
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I don't have the 16-45 , but my 35-70 f4 aperture blades close a little as I zoom out to 35mm I think it keeps it at a constant aperture f4, if the 16-45 is the same it is probably supposed to do this. I've been wrong before though,but I try not to make it a habit
tom

03-11-2007, 04:57 PM   #9
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QuoteOriginally posted by chals Quote
It is the other way around, I can see the blades in a not fully open position, even thogh the aperture i set on 4.0. when the picture is taken the blades does not open to 4 but stay at 2.8 and the picture get underexposed.

?!? To my best knowledge the 16-45 mm lens has a maximum aperture of 4. There should be no way for it to open wider (eg. to a lower number such as 2.8).

This is the DA 16-45 F4 AL lens we are talking about here, as pictured in the link below, right?

https://www.pentaxforums.com/lensreviews/showproduct.php?product=149&cat=43
03-11-2007, 05:11 PM   #10
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QuoteOriginally posted by Alvin Quote
?!? To my best knowledge the 16-45 mm lens has a maximum aperture of 4. There should be no way for it to open wider (eg. to a lower number such as 2.8).

This is the DA 16-45 F4 AL lens we are talking about here, as pictured in the link below, right?

https://www.pentaxforums.com/lensreviews/showproduct.php?product=149&cat=43
.

Yes it is the 16-45, sorry for a new typo, max open is 4, seems like it may stay at 5,6 from time to time. If I zoom back and forth a little around the 45mm area, the blades usually snaps into full open, but not always

I call Pentax tomorrow
03-11-2007, 05:18 PM   #11
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does it stay @ 4 constant, or is it like 4-5.6?


edit: n/m i just saw, it's a constant 4 through out

Last edited by -=JoN=-; 03-11-2007 at 05:23 PM. Reason: info change
03-12-2007, 06:20 AM   #12
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QuoteOriginally posted by chals Quote
.

Yes it is the 16-45, sorry for a new typo, max open is 4, seems like it may stay at 5,6 from time to time. If I zoom back and forth a little around the 45mm area, the blades usually snaps into full open, but not always

I call Pentax tomorrow
It sounds like it needs servicing. Mine stops down a bit as I zoom to 16mm, but you say yours is sticking as you zoom out to 45mm, if I understood you correctly.
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