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  1. #41
    Leigh B's Avatar
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    Quote Originally Posted by qpzil View Post
    I've always been curious about my lenses that are *slightly off* at infinity.
    Be very careful when evaluating lens performance.

    Many lenses, particularly in longer focal lengths, have a mechanical stop on the focus ring
    that's located past the normal infinity focus position.

    This is done to allow for dimensional changes in the lens resulting from temperature changes.

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  2. #42
    Steve Smith's Avatar
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    If the image in your viewfinder is in focus and your prints are equally in focus then you don't have a problem in the camera. Actual infinity focus might not coincide with the infinity marking on the lens but that shouldn't be a problem unless it is out excessively.


    Steve.

  3. #43

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    Quote Originally Posted by Mr Bill View Post


    Like this one: http://www.flickr.com/photos/2950454...n/photostream/
    It just extends the capabilities a bit.

    On this model, the focusing barrel has micrometer-like scales, with zero at the infinity-focus position.

    One use would be with respect to checking how well a zoom lens holds focus. If you refocus the Gokosha unit then read the offsets from the barrel, you can calculate the focus error of the zoom lens. Or, if the backfocus distance is in error, you could take a handful of readings, then calculate shim corrections in the lens mount.

    I don't know of any way to do these things with a pure autocollimator.
    The Gokosha on that photo is mine. It is model 24LT-2DTS which has a 193,5mm lens and is primarely designed to be used on 35mm cameras. There is a "big brother", the 32LT-2DTS which has a 300mm lens and no doubt would perform fine on MF cameras.
    The 24LT has indeed a focusing lens which can be set between -20mm till +20mm. This feature is ideal for quickly establishing the amount of correction needed for perfect infinity focus and also for checking "in between" distances.

    Sadly enough the seller didn't have a manual so i still have to find out all the details.

    The unit came with a so called "Lens Micrometer M-3" add-on (article #901) which is an unit that can be attached to the collimators baseplate and consists of a mirror which can be varied in height by means of a micrometer.
    A manual in its box descibes how to use it for Yashica Zoomtec 70 cameras. First you have to bring the cameras lens in the "adjust"mode with a special control box, then place it on the Lens Micrometer, set the collimators lens to -2.88 and then adjust the Lens Micrometer till you have a perfect collimator image. The adjustment of the Lens Micrometer should
    then be within +/- 0.04 mm.

    For MF cameras (i collect folders and TLR's) i use an old auto-collimator which was either build by Zeiss or Voigtländer. That one is twice as big as my Gokosha and has a fixed focal length.

    Allways important when using these kind of eye-sight auto-collimators is that you first have to "calibrate" the diopter by using a flat surface mirror instead of a camera-lens just before you start adjusting infinity on a lens as your eye is part of the focal system.

  4. #44

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    Quote Originally Posted by Leigh B View Post
    >>>>>If that's true, you have some seriously broken cameras.

    I'd stop short of "seriously broken", preferring "worn commensurate with age and use".

    >>>>> Point #1: The distance marked on the lens is from the subject to the film plane, not to the lens.

    Indeed. I thought I'd covered the issue of the film plane point with my words "Even allowing for the fact that the camera tripod bush location may vary relative to the film plane,"

    >>>>> The film plane is marked on all (decent) cameras by a small circle with a line running through it, parallel to the film.
    The line is the actual film plane location, and is used for all distance measurements.

    This is not news to me, though I'd hesitate to label a camera 'decent' or otherwise purely on the presence or absence of such an indication. IIRC none of my Pentaxes (inc. the LX) have this, though a more lowly Yashica TL Electro does!

    >>>>> I cannot speak to the performance of other camera/lens brands since I have no experience with them, nor examples to test.

    Likewise, I have no experience of Nikons!


    - Leigh
    Steve

  5. #45

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    Quote Originally Posted by E. von Hoegh View Post
    ....

    Edit - If the Leica rangefinder could distinguish between pins at, say, 10 feet, I'd be impressed. I wonder if a Contax II could at 10 feet? Making that test at 3 feet is giving the rangefinder every advantage - not much of a test really. Roughly 3% accuracy.
    Leica III/IIIx series (up until M series) got rangefinder magnification factor of 1.5x, and You can easily distinguish between pins at 10 feet and even 20 feet.
    Contax II or later Leicas M3, M2 etc rangefinder magnification factors are usually in the range 0.58x ~ 1.0x.. so their chances are remote.
    Thats the price You pay when combine rangefinder and viewfinder in one.
    Last edited by georg16nik; 08-23-2012 at 04:07 AM. Click to view previous post history.

  6. #46

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    Quote Originally Posted by Steve Smith View Post
    If the image in your viewfinder is in focus and your prints are equally in focus then you don't have a problem in the camera. Actual infinity focus might not coincide with the infinity marking on the lens but that shouldn't be a problem unless it is out excessively.


    Steve.
    I will go along with that, especially with some zoom lenses, the focusing marks on the barrels are pure figment of the engineers imagination.

  7. #47
    Diapositivo's Avatar
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    In my Tamron 500/8 catadioptric infinite is actually marked with a line, like an underscore __ so that the use doesn't worry about discrepancies.
    Fabrizio Ruggeri fine art photography site: http://fabrizio-ruggeri.artistwebsites.com
    Stock images at Imagebroker: http://www.imagebroker.com/#/search/ib_fbr

  8. #48

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    Well this thread has stimulated a great discussion and lots to think about, so thanks all. In my case though, I did enough shooting this weekend to convince myself that my problems are entirely due to operator error. I am lousy when I don't have a long time to focus, or when the light is low. My Nikons are mainly Nikkormats, some with split screen/microprism, some with microprism only.

    Short of going the autofocus route, any suggestions for improvement? Do the F series cameras have significantly better screens, or are they just interchangeable but not qualitatively different? Are there any add-on devices that help any way, other than diopter correcting eyepieces? I really don't want to start again with autofocus backs and lenses so I'm open to suggestions on how to improve. Or maybe I'm not that different from the norm, hence the popularity of autofocus.

  9. #49

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    I think the DG-2 magnifier will fit Nikkormats.... I originally bought one to use with my D200; the small viewfinder made it difficult for me to focus manually even with a Katz Eye screen installed. I eventually abandoned the idea since the magnifier only shows the center of the viewfinder and you have to flip it aside to compose. I still use the DG-2 for close-up photography though. I can say that my focusing accuracy has improved since I started making an effort, but I am still slow.

    The F4, F5, and F6 all have electronic rangefinders with LEDs to aid in manual focusing. Some people don't like them, but I think they work great.

  10. #50
    Diapositivo's Avatar
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    Quote Originally Posted by newcan1 View Post
    Short of going the autofocus route, any suggestions for improvement? Do the F series cameras have significantly better screens, or are they just interchangeable but not qualitatively different? Are there any add-on devices that help any way, other than diopter correcting eyepieces?
    I think focusing aids, such as green lights of AF devices, are really helpful only when there is a non-correctable sight defect. If your sight is fine, or if it has a defect that can be corrected with a diopter in front of the eyepiece (or contact lenses, or glasses) than I would rely more on traditional focusing methods.

    For critical work you could apply one of those magnifying finders which can be easily turned over. When focus becomes critical you turn the focusing aid in front of the eyepiece, and in normal use you don't use it.

    When doing portraits the focus point should be centred on the nearest eye. This is important. Focusing on the tip of the nose, or the furthest eye, will cause a sensation of defocus and you will not remember any more where exactly you were focusing. The focus point must be chosen accurately.

    In macro work sometimes it is not easy to chose the focus point. For insects it is normally the eye (or the nearest eye), for flowers it is normally the tip of the pistil.

    Don't rely on depth of field indications on the barrel for focusing. Acceptable focus is not the same as very good focus. Always choose which is the important focus point of your subject.

    It might be that you focus accurately but don't think carefully about where to focus and when observing your results you feel a sense of focus deficit, when the problem was just in focus planning so to speak.

    Generally speaking, focusing has its importance but shouldn't detract too much from other technical aspects of photography.
    Fabrizio Ruggeri fine art photography site: http://fabrizio-ruggeri.artistwebsites.com
    Stock images at Imagebroker: http://www.imagebroker.com/#/search/ib_fbr

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