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PostPosted: Wed Nov 09, 2011 7:22 pm 
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Joined: Tue Aug 31, 2010 8:23 pm
Posts: 126
Hi all
If anyone's up for it that owns this lens could you have a look to see what the aperture does when you get to 16mm, like maybe open up slightly.
Im trying to work out why mine over exposes from about 14 to 16mm.
I think i know why but just need to check against a fully working copy, which i don't have!


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PostPosted: Wed Nov 16, 2011 9:42 am 
What do you mean? I can shot at aperture f/2.8 at 11-16mm


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PostPosted: Wed Nov 16, 2011 8:24 pm 
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Joined: Tue Aug 31, 2010 8:23 pm
Posts: 126
Hi
What im trying to find out is if the actual diaphragm opens slightly as you zoom to 16mm compared to 11mm.
Best way to see this is either using the depth of field button on the camera if there is one and seeing if the viewfinder get brighter or changes as you zoom to each end whilst holding the button down. Setting to f22 while doing this should make it more visible if it does.
Also taking the lens off the body and just holding up to the light while viewing the hole size from the rear whilst zooming.
On mine it opens slightly from 14mm and it over exposes from 14mm to 16mm, camera meters ok but its definitely not ok!!
I have to knock it back a stop when at 16mm to get exposure more balanced.
There's a internal bar that links into the diaphragm blades and as you zoom it travels along it, hence opens more at one end.
I don't think it should do this, but have nothing to compare against.
Hope that makes sense!
Cheers


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PostPosted: Sat Dec 10, 2011 7:12 pm 
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Joined: Tue Aug 31, 2010 8:23 pm
Posts: 126
Still don't really know what should happen with this lens as you go to either focal length.
In the end i pulled the lens apart and lubricated the aperture linkage and the return spring on the actual diaphragm as it drags over the internal barrel so there's friction at that point.
Also moved the bar that opens up the diaphragm so it does almost does the opposite, closes down slightly at 16mm than open up.
Its made it more usable for me and its not over exposing so much now.
There's still a bit of a difference between both ends but nowhere near as bad.
Maybe the aperture hole sizes aren't correct now, but i use it in AP mode so let the camera do the shutter speed or drop it into manual.
Wonder if they just set these up wrong at the factory??


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