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07-23-2012, 04:17 PM   #1
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Vivitar 70-150 mm close-focusing lens

Last spring I was induced to buy an old Kodak 35 mm Signet camera for $5 at a flea market in Florida. I didn't want to buy it since I collect old mechanical cameras and I already had a Signet. The seller told me that if I bought the camera he would give me a free lens which turned out to be the Vivitar 70-150 mm. I got both for $5. When I got home I found that it had a Pentax screw thread and I was able to mount it on my K100D since I had fitted an adapter to it. This lens is top rated by the Pentax Forum, and it is the two-touch version which has a ring for zooming and another for focusing. The lens was in mint condition with a bit of dust, or fungus, behind a frontal element. I had it cleaned and lubed for $50. Here's my question. When I turn the focal length ring to "close-focussing" to take a shot, I have to move the lens to about 12 inches from the subject. I cannot tweak the sharpness by adjusting the distance ring. I only get a sharp picture at 12 inches. Moving the focus ring from 5 feet to infinity has absolutely no effect on sharpness of the image even though the lens changes its physical length. It's as if the close-focus setting disengages the focusing mechanism of the lens and the only way to get a sharp picture is to move the camera to a set position. However, this doesn't make sense since the front lens elements may be moved without changing the focus. I would think that any change in the position of the elements has to cause a change in the focus point. Can any learned person enlighten me?

07-24-2012, 05:19 AM   #2
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My 75-205 has the same setup. It's just how the elements/glass are stacked for the macro/close setup.
07-24-2012, 09:24 AM   #3
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Thanks aTomx. Good to know that my lens is behaving "normally", even though I can't understand how the lens maintains focus while the distance ring is rotated from 5 feet to infinity. Very strange!

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