Focus at infinity

Discussion in 'Landscape' started by bri, Jun 25, 2005.

  1. bri

    bri New Member

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    Hello everyone
    I have a 500C/M with standard 80mm T* Planar lens. I have noticed recently that it does not appear to focus at infinity. Using the cross hairs in the centre of the screen, objects will not line up correctly at distances over about 100 metres.
    Is this something I could fix, or would it be preferable to send the camera away for adjustment? Could anyone tell me where to send it in the UK?
    Thanks in anticipation
    Brian Parker
     
  2. simonpg

    simonpg New Member

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    Brian, I presume that you mean the lens focuses short of infinity. That is when you aim the lens at an object at "true infinity" the lens needs some more ring turn to sharpen up. True infinity is what I call a distance say a mile away - welly beyond the 30 plus meters the markings on the lens barrel indicate as the last distance measure before the infinity marking.

    If my interpretation is correct, then this is nothing to do with the camera. It is the lens that needs adjusting.

    Yes, have the lens inspected and adjusted by a technician. It needs adjustment to allow the focus ring to move further - it may only be a couple of mm further throw.

    In fact most lenses have a focus ring throw a little bit beyond infinity especially on SLR type lenses. This helps to compensate for changes caused by hot temperatures.

    I have never had this problem on a Hasselblad lens, but did on a new Leica - M lens, which the factory agreed needed a 1mm adjustment.

    NO, you should not attempt to fix this yourself as it needs special equipment to get it right.
     
  3. bri

    bri New Member

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    Thank you Simon Yes, you are correct. The lens focuses short of infinity. I will do as you say, and seek professional help Best wishes Brian
     
  4. simonpg

    simonpg New Member

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    You're welcome Brian. It's a quick and easy BUT a precision thing to do. Unlike rangefinder camera lenses, SLR lenses really nead to have some focus ring throw a fraction beyond infinity - for reasons of both temperature changes and ease of seeing critically sharp focus at true infinity.

    You may notice when focusing SLRs that being able to go to sharp focus and then over focus and back again, allows you to be sure you have critically sharp focus at infinity. Rangefinders have a benefit in that all you need to do is go to sharp focus and rangefinder officiandos comment on these cameras' quicker focusing in that there is no need to "wiggle among aparent sharp/under/over focus" to get critically sharp focus. Hence rangefinder lenses typically often have no "over focus" play beyond true infinity.
     
  5. cs_foto

    cs_foto Member

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    I am pretty amazed at how common this problem is..

    too bad no-one (elsewhere) advices hasselblad's second-hand prospective buyers!

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