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  1. #1
    Rob Skeoch's Avatar
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    400 Lines per Millimeter... what does this actually mean

    Hi guys,

    I was looking up something on the Zeiss M 25mm 2.8 on wikipedia.
    It says "Zeiss made a milestone in resolution with this lens. 400 Lines per Millimeter."

    What does this actually mean?

    Is it true? How do we know?

    So does this mean this is the only lens to reach 400 LPM?

    Does this make the 25mm the sharpest lens in photography?

    Of course on a personel note my pictures with this lens might be sharper.... but still boring.

    -Rob
    Rob Skeoch
    This is my blog http://thepicturedesk.blogspot.com/
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  2. #2
    BWKate's Avatar
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    I have a Zeiss T* Distagon 25mm 2.8 lens for my Contax 139 35mm camera. Is it similar to the lens you are talking about?

  3. #3
    nyx
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    Quote Originally Posted by BWKate View Post
    I have a Zeiss T* Distagon 25mm 2.8 lens for my Contax 139 35mm camera. Is it similar to the lens you are talking about?
    No, this is Biogon design for Leica M bayonet mount.

  4. #4

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    Well, depends on your point of view.

    If you take any other lens designed for the 35mm format and compare it to the lens in question, you will find out that if you photograph resolution charts, it will out-resolve any other 35mm format lens. This is what it means.

    However, you will likely still get a higher resolution image out of many 4x5 or medium format setups, because actual resolution just isn't that simple.

    Also, the resolution of the lens in an ideal test case doesn't necessarily cover how a lens actually performs in the real world under real photography cases. It could suffer from flare or bad bokeh. Or your particular camera could have the lens mount off in one way or another. Or your particular lens could be slightly misaligned. Or you could be shooting 20asa microfilm and suffer from camera shake. Or your negative holder could be off by a fraction of a mm. Or your enlarger lens could be the weakest link. Etc.

  5. #5

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    Once upon a time the Modern Photography magazine that was published an article on getting 100 lp/mm on film. Short answer, with a high contrast target, very slow, sharp film, meticulous technique, a very good lens and some luck it can be done. It can't be done consistently.

    This old story's relevance to Zeiss' claim of getting 400 lp/mm on film is that in most photographic situations resolutions on film anywhere near that high are unattainable. Until convinced otherwise, I'm going to believe that the real meaning of Zeiss claim is that owners of their wonder lens will have braggin' rights. Also that any capable photographer using perfectly ordinary LF equipment will be able to produce better large prints than the braggarts.

  6. #6
    naaldvoerder's Avatar
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    I don't think the abillity to buy this lens is much to brag about, making it is however....

    I think the test were done on gigabit film, which apperently is highly resolving itself

    Jaap Jan

  7. #7
    Jim Jones's Avatar
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    400 lp/mm is certainly high for consumer grade 35mm cameras. A single number doesn't tell all the story, though. Does the lens attain this resolution only on-axis? A Nikkor 20mm f/3.5 I used decades ago was extremely sharp in the center of the field, but a few magnitudes less sharp in the corners. Is it determined by measuring the aerial image or (less likely) on film? Is it determined in white light or monochrome light? If monochrome, what color? What is the contrast of the target? Remember, wikipedia articles may not be reliable. Even I (perish the thought!) could submit one.

    I don't know what the resolution requirements for integrated circuit masks are, but they must be higher than 400 lp/mm.
    Last edited by Jim Jones; 01-26-2007 at 09:42 PM. Click to view previous post history.

  8. #8
    rfshootist's Avatar
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    Quote Originally Posted by Rob Skeoch View Post
    Hi guys,

    I was looking up something on the Zeiss M 25mm 2.8 on wikipedia.
    It says "Zeiss made a milestone in resolution with this lens. 400 Lines per Millimeter."

    What does this actually mean?

    -Rob
    Actually nothing. At least not in practical life.
    Only if photographing test patterns is your hobby, shooting TechPan on a tripod and developing it to 100% contrast.
    Zeiss feeds those nerds who TALK about lenses instead of using them. In other words the majority in the crowd of the "serious" amateur photogs !

    Regards,
    bertram
    A la recherche du temps perdu: www. bersac.de

  9. #9

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    Resolution alone is not a very useful metric for comparing lens sharpness. MTF is vastly more important. All normal photographic films (excluding microfilms, etc.) have an MTF response of zero at 400 lp/mm. Likewise, the aerial image of the Zeiss lens itself probably has an MTF very close to zero at 400 lp/mm. Consider that 400 lp/mm is around the diffraction limited resolution at f/4. So the lens had to produce this figure somewhere between wide open and f/4. It's very likely that at these f-stops the lens has substantial aberrations. Wavefront error alone would cause pretty low contrast response at these f-stops.

    So even if the lens resolved 400 lp/mm in the aerial image, it might have lower contrast response at 20 lp/mm than another lens incapable of resolving 400 lp/mm. As the contrast transfer at 20 lp/mm is actually useful for determining how sharp a photograph will look (on 35 mm film at least), the 400 lp/mm figure seems to be a bit of red herring: useful insomuch as it sounds good to the Zeiss marketing department, but I bet the engineers are none to happy about the claim.

    This is not to say that the lens isn't sharp. In fact, the MTF charts (PDF here) are outstanding. But you'll notice the lens is sharper (or has better contrast transfer at 10, 20 and 40 cycles/mm) at f/5.6 than at f/2.8, proving the pointlessness of the 400 lp/mm claim: at f/5.6 the lens is theoretically incapable of resolving 400 lp/mm, yet performs better in the real world at this aperture than wide open.

  10. #10

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    Quote Originally Posted by rfshootist View Post
    Actually nothing. At least not in practical life.
    Exactly. No useful film can resolve it; no camera can hold the film flat enough, repeatably enough, to record it, even if the film could.

    Yes, it's a super-sharp lens. You should be able to get 100-125 lp/mm on the film quite often -- and there are damned few lenses that can do that.

    Otherwise, this is Wikipedia at its best: the blind leading the blind, by blinding them with pseudo-science and 'factoids'. A 'factoid' is a statement that purports to be factual and may even be defensible (as this is for aerial resolution), but is neither adequately qualified nor actually demonstrable.

    Cheers,

    R.

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