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Thread: Compendium Shade Extension or Mask... Which is More Effective?

  1. #1
    Scott Rosenberg's Avatar
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    Compendium Shade Extension or Mask... Which is More Effective?

    good day... a question for the physicists among us. i did some very basic experiments and decided that a compendium lens shade would improve my photography. i then started researching various options and was quite surprised to find the linhof shade to fit my tech IV was ridiculously overpriced and wouldn't extend far enough to be all that effective. long story short, i bought a used lindhal bello-shade, carefully took it apart, and then reassembled it using $4 worth of hardware to fit into the two holes on the top of my front standard. works great, cost me less than $30.

    the openings of the shade are about 4" square. my question it thus... with an opening this large, i can pull the shade out nearly a foot without any vignetting on my 300mm lens with successively lesser amounts of extension for my shorter lenses (240, 150, 110). is it more effective to have a mask at the end of the bellows and less extension or not to use a mask and simply extend the shade to just short of vignetting? the light theory i can recall, from many years ago, would lead me to believe that there would be no difference whatsoever in the effectiveness of either method; wind buffeting from the long shade withstanding. though it has been a while for me, so i thought i'd ask the forum and see what response i got.

    thanks, scott

  2. #2
    Moderator Ralph Barker's Avatar
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    Compendium Shade Extension or Mask... Which is More Effective?

    I'm certainly not an optics expert, Scott, but it would seem to me that once stray light hits the front element of the lens, it's tough to say where, and at what angle it will bounce - particularly if strong enough to start bouncing between element surfaces. Thus, I'd lean toward a bellows-style shade of the optimal length for the lens. A mask at the back of the shade, in contrast, won't work conveniently with movements.

  3. #3

    Compendium Shade Extension or Mask... Which is More Effective?

    To extend the shade just short of vignetting is a much more efficient method than just having a mask as you describe. Having the lens shade longer makes the angle of flare causing light smaller. The lens shade is not there just to follow the lens angle of view cone.

  4. #4
    Scott Rosenberg's Avatar
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    Compendium Shade Extension or Mask... Which is More Effective?

    thanks for the responses, fellas. i guess i won't bother making masks for the front opening of the shade, but rather will extend the bellows out as far as i can without causing vignetting.

    thanks again, scott

  5. #5
    Whatever David A. Goldfarb's Avatar
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    Compendium Shade Extension or Mask... Which is More Effective?

    Having used bellows and compendium shades for a long time, I would recommend extending as far as you can, but making a mask if you use very long lenses for the format, just to avoid problems of the shade sagging or becoming a source of vibration outdoors. Usually one or two masks is enough, and they don't take up much space or add weight to the kit.

  6. #6
    Robert A. Zeichner's Avatar
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    Compendium Shade Extension or Mask... Which is More Effective?

    In the motion picture industry hard mats as they are called, are used frequently as opposed to compendium shades. They usually come in sets for each focal length of lens. These are very effective and I suspect an improvement over compendiums for the following reason. When you extend a compendium, the angle of incidence of light rays striking the inside of the bellows is such that even the relatively non-reflective material that the inside of the bellows is made of starts to reflect these rays back toward the lens. An ideal design would consist of a series of flat black baffles that are perpendicular to the optical axis of the lens. That sort of assembly is occasionally what you will see inside the lens box of higher quality still cameras, but would be tricky to do in a compendium as it needs to adjust for different angles of view. A single hard mat is pretty easy to make and if flat black, will not reflect any significant amount of light back to the lens. In a view camera though, there is the added problem of the lens projecting a cone of light larger than the film area, this for the coverage needed for use of movements. Coupled to the portion of light the film doesn't "see" is an associated area of coverage in front of the lens that one misses when looking at the ground glass. So the issue of what size to make a hard mat is less than obvious. Complicating matters is that when the lens is opened up for composing and focusing, any vignetting caused by a too small hard mat (or shade) might go unnoticed. That's happened to me more than once I can assure you. Subject to film plane distance is a variable one must consider as well because coverage "improves" the closer you get. One could also argue that a similar sort of light baffle might improve contrast if installed somewhere in the camera bellows to prevent a similar kind of problem behind the lens. Where do you stop? I'm all for effective shading of the lens to prevent flare and reduced contrast, but at some point, we have to start making exposures or the light will go away.

  7. #7

    Compendium Shade Extension or Mask... Which is More Effective?

    The variables that influence the size of a lens shade for a given lens are: the lens focal length, the lens diameter, the film format, the length of the lens shade. The subject to film plane distance is irrelevant as it doesn't change the lens angle of view. Also, the longer focal lengths do not need automatically a longer lens shade, prone to sagging - they usually need a smaller aperture of the lens shade, due to the smaller angle of view and therefore a smaller lens shade. Thus an effective lens shade for a wide angle is always bigger than a lens shade of the same efficency constructed for a longer focal length.

  8. #8

    Compendium Shade Extension or Mask... Which is More Effective?

    Sorry, I mixted it up in the former thread . For the variables it should read - the lens angle of view, the lens diameter, the film format, the length of the lens shade.

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