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07-21-2008, 02:54 AM   #1
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another neophyte question

Hello,

So, I have this 28-80/3.5~4.5 Pentax A lens. The focusing circle at the center of the viewfinder is horizontally divided into two hemispheres and depending on the situation either one of these areas becomes partly or completely dark. I intuitively suspect that this signifies me that something ain't right, that I shall change my POV a tad in order to correct this. Am I right? Is this behaviour a common thing in all lenses? Cause I've noticed that with a 50mm/1.7 prime (used with a Minolta xg9) this does not happen.

Enlighten me on this, please.

07-21-2008, 06:24 AM   #2
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QuoteOriginally posted by lazyeye Quote
Hello,

So, I have this 28-80/3.5~4.5 Pentax A lens. The focusing circle at the center of the viewfinder is horizontally divided into two hemispheres and depending on the situation either one of these areas becomes partly or completely dark. I intuitively suspect that this signifies me that something ain't right, that I shall change my POV a tad in order to correct this. Am I right? Is this behaviour a common thing in all lenses? Cause I've noticed that with a 50mm/1.7 prime (used with a Minolta xg9) this does not happen.

Enlighten me on this, please.
Split image focusing aids go dark at smaller apertures, generally they become useless below f/4. Your 28-80 qualifies in this category. You might find that if you very carefully place your eye centered in the finder, both sides of the split will stay bright, but it isn't likely, especially at the longer focal lengths where it is slower than an f/4 lens. It didn't happen on your Minolta because you were using a lens several stops brighter.
07-21-2008, 08:31 AM   #3
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QuoteOriginally posted by lazyeye Quote
Hello,

So, I have this 28-80/3.5~4.5 Pentax A lens. The focusing circle at the center of the viewfinder is horizontally divided into two hemispheres and depending on the situation either one of these areas becomes partly or completely dark. I intuitively suspect that this signifies me that something ain't right, that I shall change my POV a tad in order to correct this. Am I right? Is this behaviour a common thing in all lenses? Cause I've noticed that with a 50mm/1.7 prime (used with a Minolta xg9) this does not happen.

Enlighten me on this, please.
Try setting the aperture to f5.6 and push the DOF preview button on your XG9 and you will see the same behaviour.

Jan
07-21-2008, 09:22 AM   #4
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Original Poster
ok, thanks both of you.

You're right, Wheatfield, just moving my eye, and not the camera, a tad and the viewfinder's center stays bright.

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