#235 – Rotkanal ist ein …

Gruppenfoto Klostergeister 2011

Sommerzeit, Workshopzeit, Klostergeisterzeit. Chris und Boris verbringen gerade vier Tage mit zwanzig wahnsinnigen enthusiastischen Fotoverrückten im Kloster in Inzigkofen. Vier intensive Fototage, vom gemeinsamen Frühstück bis zum Gutenacht-Bier voll mit Kameras, Aufgaben, Projekten, Kameras, Licht und Schatten. Und auch in dieser Folge stellen die Teilnehmerfragen die Grundlage für eine ganze Sendung.

Die Fragen im Einzelnen:

  • Welche Kamera ist besser, Nikon oder Canon? Wie bekommt man beim Makro die Beinchen scharf?
  • Sepp kündigt den Review von Photosmith an
  • Was bedeutet die Einstellung des four-thirds-Formats bei Olympus?
  • Wie vermeide ich den überbelichteten Rotkanal bei Blumen?
  • Warum ist das Bokeh hinter der Schärfe schöner als das Bokeh vor der Schärfe?
  • Warum sieht das Bokeh im Sucher anders aus als das Bokeh auf dem Foto?
  • Unser Workshopdrucker ist diesmal der Canon Selphy CP800

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7 thoughts on “#235 – Rotkanal ist ein …”

  1. Warum sieht das Bokeh im Sucher anders aus als das Bokeh auf dem Foto?

    Neulich habe ich die gleiche Entdeckung gemacht, das irgendwie das Bokeh im Sucher nicht stimmt mit das Bokeh auf dem Foto. Leider ist mein Deutsch nicht so gut, deshalb antworte ich auf Englisch. Vielleicht kann jemand anderst meine Antwort übersetzen.

    I noticed two viewfinder phenomenon that I didn’t understand, yet upon further thought, I think they are related. To my surprise, one of them came up in your podcast today.

    I was taking pictures at a volleyball game with my Canon T1i and a recently purchased 85 mm f/1.8 fixed-focal length lens. Since it was fairly dark, I was shooting at f/1.8, that is wide open. Since my lens was wide open, I assumed that the aperture would not close during the shooting of a picture, and therefore expected the view in the viewfinder to match the final photo as viewed on the back of the camera. However to my great surprise, I noticed that my pictures as seen on the back of the camera had significantly smoother out-of-focus backgrounds than those I saw in the viewfinder. A sharp edge deeply out-of-focus in the background had a much smoother transition on the display than it had in the viewfinder. However after retaking the photo at f/5.6 showed almost no difference between the aperture previewed viewfinder view and the back of the camera.

    I then tried watching the viewfinder with the aperture preview engaged and simultaneously adjusting the f/number. As expected, as the aperture was being opened, the viewfinder view became progressively brighter and the bokeh became smoother. However at f/numbers below f/2.8, I no longer saw these changes. This suggested to me that somewhere in the light path between lens and output of the viewfinder, another aperture of around f/2.8 must be present. At first I thought it might be the optics of the viewfinder itself, but I couldn’t believe that if more light is incident on a ground glass, it ought to somehow get brighter. But then I realized that maybe the ground glass isn’t what one thinks it really is.

    At that point I remembered the other phenomenon I sometimes see. When my lens is very out of focus, sometimes the out-of-focus areas appear almost pixilated, at a minimum regularly textured. This suggests that the ground glass actually is mechanically textured, probably with multitudes of microprisms or microlenses. When light hits these micoprisms at a higher angle of incidence, the light no longer transmits through the prism and into the viewfinder, rather the light gets lost somewhere. In effect high-incident light is eliminated, just like the effects of an aperture! The texture of the ground glass can account for both effects.

    As one looks through the viewfinder, one is looking at an image that is usually limited by the aperture of the lens. However for very large aperture lenses with apertures less than f/2.8 (for a Canon T1i), then the textured ground glass limits the view. Aperture preview therefore is WYSIWYG only for apertures greater than f/2.8.

    By the way, my father had an old Canan Ftb/QL. It’s ground glass included a split prism focusing feature at the center of the viewfinder surrounded by a fairly coarse microprism ring. When something was out-of-focus, the microprism area became speckled, indicating light must have been scattered out of view. Remembering my father’s old camera aided my thought process.

    I love your show.

    3-2-1 HappyShooting.

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