Strange Effect of my Leica M 35mm Summilux (pre-ASPH)

Discussion in 'Leica and Rangefinders' started by ewanc, Sep 3, 2007.

  1. I just joined the Leica M world a month ago with a purchase of a M6 classic black and a 35 Summilux.
    I have taken quite a few rolls with it; I am very happy with the lens, as it exhibits a very soft, dreamy bokeh that is not seen with most of my Nikon WA lenses. However, I did find in some photos that I took with this lens a strange effect with the way artificial light sources (such as the red traffic light) gets washed out. (See photo below.) Even though I was using a slow shutter speed, I am sure the effect was not caused by camera shake as then everything (the people, the objects) in the photo should appear blurry, but they are not.
    [​IMG]
    My question is: 1) Is this what people mean by chromatic abberation? If not, what is this effect called and what is it caused by?
    2) Is this effect a characteristic of this lens in general or is it just my sample?
    Thanks in advance for any answers.
    Photo data: Fuji Provia 100, exposure probably f1.4, 1/15 sec
    p.s. there are 1 or 2 tiny scratch marks on the lens, even though I don't think it should be the cause of the effect.
     
  2. hi
    1)this is the effect called coma. try to stop down to avoid it.
    2)not only your sample, almost every 1,4 WA lens have this effect wide open.
     
  3. I don't think it's coma, which should be radial to the lens axis. But I could be wrong. How about ordinary flare?
     
  4. I believe this is due to camera movement; slight movement blurring will be more evident with bright lights than underexposed areas.
     
  5. Umut has it. It's particularly pronounced with the 35 lux pre-asph wide open and shows especially with strong highlights. Stop the lens down to f2 and it's practically gone.
     
  6. Thanks to everyone for chiming in.

    After Umut suggested it was coma, I did some more info-digging and I am inclined to think both Umut and Lutz are right. I will do some further tests on a tripod and compare both wide open and stopped-down shots, and report my findings at a later date.

    Now assuming this is indeed coma, the $2500 dollar question is whether the fancy ASPH 35'lux would handle it better at wide open. Not that I have the means to get such an expensive lens, but doesn't hurt to wonder.

    Happy shooting!
     
  7. Ewan, with the asph version coma is much more contained. BTW, try this link for a comparison on bokeh.
     
  8. I believe Gary Sandhu has the right answer (including the right reason why you only notice the effect with the lights) and that it is not coma for the reason Dave Sims has stated. If it were coma, the "tails" would point away from the optical axis. In your photo, tails on opposite sides of the axis each seem oriented along the diagonal running from top left to bottom right.

    In any event, this is easily tested with a tripod. If it's coma, you should see the same effect every single time.
     
  9. Which version of the pre-ASPH 35mm do you have ? I heard (and have seen example photos) of the 1st version of this lens being more prone to flare due to internal reflection.
     
  10. Hello Lutz, thanks for the link. A fascinating read... it seems everyone has a different opinion regarding the bokeh of those two lenses. (Which, I suppose, is the norm for these kinds of discussions?)

    Gabor, I think I have the fifth version. It's black, and has an engraved "35" on barrel. And says "Made in Germany".
     
  11. This is clearly a lens aberration, rather than subject/camera movement during exposure. This aberration, increasing with image height, is often seen in photos taken at a large aperture with fast double-Gauss designs. It is particularly obvious with light sources, but it affects all image-forming light, reducing localised contrast (so in your example photo, light from the sky will have been pulled into the dark areas of the lamp posts, reducing the contrast of the posts against the sky).
    It's true that this aberration is often referred to as coma, but I'm not sure how accurate that is. Strict coma artefacts are comet-shaped, with the tail pointing away from the centre of the image. That said, Nikon refer to the butterfly-type aberration in your photo as sagittal coma flare, and include demonstration photos:
    Nikon 1001 Nights article on Noct Nikkor
    But the translation of that article is not very rigourous so perhaps the aberration is also inaccurately translated. I have also heard it described as sagittal oblique spherical aberration, but normal spherical aberration increases dramatically with aperture but not with image height, whereas the butterfly-type flares seen in your image increase strongly as image height increases. So in short, I don't know what it's called!
    Suffice to say that it is most definitely a common aberration in high speed double-Gauss designs, and in particular, fast wide-angle double-Gauss designs, which exactly describes your pre-ASPH 35 mm Summilux. I've seen it in practically every similar photo taken with the pre-ASPH 'lux wide open, so by all accounts it is an inherent characteristic of the pre-ASPH 'lux, and not unique to your sample.
     
  12. Samuel, your contributions are as informative as always and well documented, too. Thanks a lot!
     
  13. I think there's too much mess about average and not interesting picture. So what, th ehell, is more important? Picture or equipment?
     
  14. Jacek,
    You might want to consider that this "mess" is about understanding why the effect occurred for reasons having little to do with this single frame of film. About your question: can you make a picture without the equipment? In the end, i have a feeling Ewan simply wants to know that he can make the kinds of pictures HE wants to make and not have them dictated by an equipment-specific 'peculiarism.'

    Why are you so indignant? You're in a Leica forum. If you'd rather not discuss equipment, you're wasting OUR time.
     
  15. Many people will call it coma, but that is not correct. The aberration causing this is sagittal oblique spherical aberration. True coma is never a problem in photographic lenses used at or near their optimum magnification. The only exception still encountered these days is Newtonian telescopes.

    Brian
     
  16. Cheers, Lutz!

    Brian: is it possible to explain, preferably without terms of art, how a spherical aberration becomes dramatically worse as image height increases? I am struggling to imagine how a spherical aberration could behave like that. I don't doubt your authority on the matter. In fact, I think it was your definition of this aberration as sagittal oblique spherical aberration that first alerted me to the notion that it may not be coma (I had thought it was coma but somehow affected by artificial vignetting).
     
  17. Lens aberration - regardless of which name is correct (I've always seen this called coma,
    myself).

    Classic signature of the Leica pre-ASPH 35s. Here's an example from the v. 4 'cron,
    compared to the ASPH f/1.4, from a few years back:

    http://www.photo.net/bboard/big-image?bboard_upload_id=11090784

    Interestingly, the v.4 'cron and the pre-ASPH lux both share a 7-element Double-Gauss
    design, with the 7th element (not a Bruce Willis movie!) as a "corrector" for curvature of
    field immediately behind the aperture - and both show this butterfly aberration.

    The v.3 'cron, OTOH does not have the 7th element, is not quite as crisp, but also shows
    less of this butterfly effect as well. Optical trade-offs, I guess.
     
  18. Thank you all very much for your contributions, since knowing what it is and how to avoid it is important to me. I am deeply humbled by how knowledgeable some of you are on optics, and only wish I had paid more attention to my physics class back when I was still a student.
    Samuel: I found an example taken recently that may exhibit what you suggested re: "how a spherical aberration becomes dramatically worse as image height increases?" Here is the photo, taken, at f1.4 with the 35'Lux. The light sources are a little higher than the original photo that began this post, and the coma effect seems to be a bit more pronounced as well. Also notice how the coma is more angled as it deviates more from the center. Regards.
    [​IMG]
    Coma Example
    Leica M6 + 35'Lux
     

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