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Old 1st August 2010, 03:20 PM
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Question Lens focuses "beyond infinity"

Just picked up an Olympus Zuiko 100-200 f5 zoom in a box of bits. It's in good nick but the focus ring can be turned a couple of mm past the infinity mark. The focus itself seems to be accurate inasmuch as objects at infinity are rendered sharpest when the focus is set to the inifinity mark.

My question is - can the focus stop be easily adjusted or is it a job for an expert?

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Old 1st August 2010, 03:25 PM
DaveP DaveP is offline
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Aren't some zooms like this by design for some reason or other? I'm sure i read that somewhere.
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Old 1st August 2010, 06:52 PM
Richard Gould Richard Gould is offline
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Richard, some zooms are made to focas beyond infinity,I have two Sigmas, one 100-300 and one 80-300 that both focus beyond infinity,and the standard zooms on my Pentax autofocus do the same,Don't know why, maybe something to do with autofocus design? Richard
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Old 1st August 2010, 09:27 PM
Mike O'Pray Mike O'Pray is online now
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Richard, it might be worth a call to a guy called Ed Trzoska whom Ivor Matanle of classic cameras fame, rates very highly. He is always mentioned in any of Ivor's classic camera articles in AP. He seems to be Ivor's main repair source for a range of cameras.

His Tel. No. is 0116 2674247 which is Leicester. He might be able to quickly tell you if the lens is meant to be that way or repair it if it isn't.

Mike
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Old 2nd August 2010, 07:46 AM
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Thanks all - after a bit of web searching it does seem that some lenses are designed this way although I've never come across one before. I just need to confirm whether this is one of them, and an Olympus repair man is probably the best place to start .
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Old 2nd August 2010, 05:02 PM
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Martin Aislabie Martin Aislabie is offline
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Mirror Lenses are designed to focus beyond infinity , as the glass/air diffraction varies slightly with ambient temperature.

I don't know whether high or low ambient temperatures cause the light to bend more or less

It might be that your Zooms have similar characteristics

Martin
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Old 2nd August 2010, 07:09 PM
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I vaguely remember some early zooms having focus points that shifted during the zoom action in so much as the markings for 100mm would not be accurate for the zoom at the 200mm end of the range because the manufacturing process couldn't control the relational placement of the internal elements.

Mike
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Old 3rd August 2010, 07:46 PM
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I had a Tamron 300mm zoom lens that used to focus about 3-4mm beyond infinity.
It was an old lens, I was informed by a repair shop that I took it to that it was normal for that lens.
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Old 7th August 2010, 07:24 AM
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I've now had it confirmed that this is normal for this lens. Thanks all.
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