Hard infinity stops on 200mm Schneider lenses?

Discussion in 'Classic Manual Cameras' started by Ian Rance, Dec 12, 2007.

  1. I have the majority of lenses for the Kodak Retina Reflex. On the 200mm lens I
    have, the split image shows infinity reached at a lens marking of 30 feet. If
    I turn the lens to marked infinity, the split has gone past 'aligned'.

    Several bodies all read the same.

    Which is correct for these lenses - focused image or marked distance?

    Thanks for any info,

    Ian
     
  2. if you verified the Problem on several bodies you can exclude the misalignment of the mirror/ground glass. Thus I would saythe correct is the focused image, not the marked distance.
     
  3. I have a CZJ 180/2.8 for the Pentacon6 that has a similar "past infinity" thing. Only difference is that there infinity is at the infinity mark, but you can turn further than infinity.

    This isn't a fault, it is supposed to make focussing easier.
     
  4. Thank you for your input. On my lens, the infinity mark does not match with the focus on the screen (of a distant object). Only one way to be sure - I will run some test shots.
     
  5. Check that the rear elements of your lens were a) not installed backwards as I once did on a Soligor 200m lens or b) not unscrewed slightly as happened on my Nikkor 85mm. Both of these lenses focused past infinity. I assume your gear is OK but just in case.

    In 1999 or so a similar matter came up on the LUG. If a lens focuses past infinity it could be by design to compensate for thermal expansion of the lens. A warm lens will be longer. Focusing past infinity means making the focal length shorter -- going past the focal length not past infinity in object space. So a warm lens that focuses past infinity is OK. That said I have never experienced this effect.
     
  6. Miles raises a good point, and this is what came to mind when I read Ian's question. In fact, I once read that current lenses (Canon EF lenses to be specific) are designed with this thermal expansion in mind, so I assumed, perhaps wrongly, that older cameras may have had the same design feature. Even if this is the case though, a lens turned to infinity should be in focus, while still allowing the photographer to turn a bit farther than the infinity mark.
     
  7. My 4/300 Zeiss Sonnar focuses a bit past infinity. From what I learned about this when it concerned me, the item is designed this way so it'll reach infinity in various weather/temperature conditions.
     

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