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Tom

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Tom last won the day on 24 January 2013

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About Tom

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  1. Paul van Walree does of course differentiate between lateral and longitudinal CA. But he uses "axial color" and "loCA" as synonyms. Quote: "Longitudinal chromatic aberration, also known as axial color, is the inability of a lens to focus different colors in the same focal plane. "
  2. My question was only partly one of terminology. Even Paul van Walree uses longitudinal CA and axial color as synonyms and Roger Cicala at lensrentals or Jonathan Keller use "spherochromatism" which does lend that term some credibility too. Other people use Bokeh-CA. So those terms are neither my invention nor that of Ken Rockwell... But tell me: which is the term you think is valid? My real question was whether there can be two different effects in a lens: one that influences the colors in the near field before and behind the plane of sharpest focus and one that influences the coloration of things further behind (or before) that plane. Have you seen a lens displaying a normal amount of loCA in the nearfield but being much better corrected further away than another lens? I give you an example: my tests show that the Otus is not free of loCA in the nearfield (see the examples from the scale above). But it seems to be very much devoid of green haloing in the more distant background:
  3. When I'm testing lenses with apertures of at least f2.8 I normally test for longitudinal CA (loCA). because the magenta and green (dis)coloration is one of the aerations that really annoy me. When looking into this subject I experienced that CAs vary with the distance of the subject in focus and also with the distance of the subject that is out-of-focus. Let me explain: 1. There is the effect that you observe typically around the plane of sharpest focus a few centimeters before and behind the point of focus. This is what I'd call "near-field loCA". This gets clearly worse with any large aperture lens that I've tested the closer you focus. See the following image: 2. And then there's the effect of green halos around white background subjects that are a bit further away from the plane of sharpest focus. This is what I'd understand being called "Bokeh-CA": Unfortunately I have not (yet) seen someone distinguishing between both forms of longitudinal CA and someone like Ken Rockwell is explicitly putting them all in the same basket: longitudinal CA, spherochromatism, Bokeh CA and axial color are all the same to him. Also Paul van Walree over at http://toothwalker.org/about.html does not differentiate between these effects. So my questions to you are: - Do you recognize different axial CA of your lenses in the near-field vs. further in the background? - Do you use different terms for both effects?
  4. Whoa, just read through the thread (not every post). But it seems like one thing remained unanswered: Is live-view on the Df better than on the D800? 'Cause I really hate how LV on the D800 manages to produce nasty aliasing artifacts. Never can do any critical focusing easily on it for my reviews. As Bjorn mentioned somewhere: Sometimes it's easier to judge (change of) longitudinal CA for perfect focus than to rely on sharpness in the magnified view. But alas: the Df is "only" 16MP so no platform for lens-testing...
  5. Tom

    New AF-S 58mm f1.4G

    Tried again. Now search works fine...
  6. Tom

    New AF-S 58mm f1.4G

    @Bjørn: Thanks! @arthurking83: That's funny, I used the search for "58" and "58mm" w/o success. Tried it again, still can't find the thread you linked to. What am I doing wrong?
  7. Tom

    New AF-S 58mm f1.4G

    Hello Bjørn, couldn't find any post regarding the new Nikkor. Do you already have one in your hands, got some first impressions?
  8. Hehe, this flower doesn't grow in the snow - it was just inside sitting on a window-sill with the snow outside The VR works pretty good on my copy of this lens and it is very useful in shooting close-ups.
  9. Tom

    Cosinus Phi ... whatever

    Hmm, thanks for the information. Now I only have to think about which part of the light fall-off of the new Sigma 35/1.4 comes from clipping and which is "natural". Not enough tests so far to answer that - and it's not clear to me whether clipping and "natural" fall-off add up or not...
  10. Who can tell me what the "geometrically unavoidable" light fall-off of a wide angle lens is? If that lens is not a fish-eye, that is. Afaik there is are two factors for real-life light fall-off: the one that can be calculated from the angle that light hits the lens and the one that is induced by "clipping", i.e. restriction of light through elements of the lenses body (in addition to the aperture). Not sure whether I use the right terminology... But to be more precise: What is unavoidable the light fall-off of a 35mm f1.4 lens in the FX-corner (angle of view = 63°), and in the DX-corner (angle of view = 44°)? And how do you calculate this?
  11. Tom

    Pattern

    Not sure whether the image belongs into this category. But I thought snow is a topic for nature and so are patterns in it - even if the mechanical nature of the beast that made these tracks is obvious. Shot with AF-S 35/1.4G. Enjoy! Tracks 63228 by Tom, on Flickr
  12. Unfortunately I forgot the name of this very interesting and exotic flower but I finally came around to shooting it. As it was against a backdrop of snow I had to compensate exposure quite a bit. But at least the background was not distracting this way... Shot with AF-S 105/2.8 VR. Exotic 63301 by Tom, on Flickr Addendum: Ah yes, it's a Ceropegia!
  13. What is abstract? Does every photo contain a degree of the abstract e.g. because it is only two-dimensional? Or black&white? Well these are questions that I try to deal with in my blog rotomerge.blogspot.com. The following image of a forest in the snow does not only contain abstractification by mapping 3D to a two-dimensional viewing space and taking all color (or at least what little was left there) away but also did some heavy post-processing to give the forest a ghostlike appearance: It's like looking at an X-Ray... Ghost Wood 63200 by Tom
  14. A very balanced article that makes a lot of things clear about DxOmark's measurements. Gordon Laing's review of the D800 noise/resolution at downsampled output-sizes confirmes that per-pixel noise comparison is almost irrelevant.
  15. Tom

    Wall of clouds

    The sky stayed clear and temperature dropped 3-4 degrees immediately and the following night dropped further significantly below zero (Celsius).
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