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Painting dome surfaces

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  • pauldavidbourke
    I m trying to find information on the ideal paint for a large dome surface .... in particular what gain/reflectivity and level of matte/gloss. This is for an
    Message 1 of 3 , Jan 11, 2007
      I'm trying to find information on the ideal paint for a large dome
      surface .... in particular what gain/reflectivity and level of
      matte/gloss. This is for an existing dome that is going to be used for
      full dome video style projection. Ideally seeking practical advice, the
      painting needs to be perfomed "soon", ideally before the rest of the
      interior is decorated.

      Post replies to this group if you like but I equally encourage direct
      email to paul.bourke@...
    • Ed Lantz
      Paul writes:
      Message 2 of 3 , Jan 11, 2007
        Paul writes:

        <<I'm trying to find information on the ideal paint for a large dome
        surface .... in particular what gain/reflectivity and level of
        matte/gloss. This is for an existing dome that is going to be used for
        full dome video style projection. Ideally seeking practical advice, the
        painting needs to be perfomed "soon", ideally before the rest of the
        interior is decorated.>>

        Dome painting is a tricky endeavor, and you will have to live with the
        results for a long time! I'd recommend contracting the work to one of the
        dome manufacturers who specialize in this.

        Ideally the dome should be as flat a finish as is available (Lambertian
        surface that reflects equally in all directions). Unfortunately, flatter
        paints tend to soil very easily and can be difficult to clean. Any specular
        component (where reflected brightness is a function of the angle of
        reflectance) foils multi-projector edge-blending, since the relative
        intensity of the overlapped projectors will vary depending on where the
        viewer is positioned in the theater. With a center mounted fisheye
        projector, a slight specular component (referred to as "gain") will provide
        a brighter image for people sitting towards dome center and cross-dome
        scatter is actually reduced. However, controlling the specular component on
        a painted surface is extremely difficult, so a flat finish is best.

        Dome reflectance or reflectivity (assuming a flat finish) is typically in
        the 0.23-0.55 range. Darker domes (0.23-0.38) are preferred since this
        reduced cross-dome scattering which limits contrast for fulldome imagery
        (less of a problem with stars, which is why older planetariums have
        reflectivity up to 0.7-0.8 or 80%). However, if your fulldome system is not
        very bright (i.e. CRT projectors on a large diameter dome) you may want to
        push the reflectance up a bit as a compromise, since a "darker" dome
        essentially darkens the image. Ideally, you would use a very dark dome
        (0.2) with a very bright projector. If it is a perforated dome it is
        probably already something like 20% void, so you need to account for this.
        Above around 0.5 reflectivity the scatter is particularly bothersome and
        bright images will really wash out the dome. Be sure that your
        low-reflectance paint is neutral density (grey).

        Ed
        ed@...
      • Stephen Schaffer
        When we replaced our dome, we purchased a used perforated aluminum dome from Ash. After it was assembled and installed, Ash arranged to have it repainted by
        Message 3 of 3 , Jan 16, 2007
          When we replaced our dome, we purchased a used perforated aluminum
          dome from Ash. After it was assembled and installed, Ash arranged to
          have it repainted by Astro-tec, who did a terrific job. Astro-tec
          has a special paint formulation that does not fill the holes, yet
          covers all sorts of scuffs and marks. It dried so quickly they were
          able to do multiple coats in a single day.

          Because they sprayed it on, there was quite a mess on the floor below
          the dome, but it was a water-based paint and cleaned up easily. As
          the sole employee of our institution, I got the job of pushing the
          scaffolding around the theater while the Astro-tec employee sprayed
          on the paint - I almost matched the dome color by the time we were done.

          We had our previous dome painted by a well-recommended local
          painter. They used standard paint and spray equipment, and did a
          terrible job. I highly recommend you choose someone like Astro-tec
          who knows about domes.

          Steve Schaffer
          Argus Planetarium
          schaffer@...
          www.aaps.k12.mi.us/aaps.planetarium/home
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