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  1. #71
    holmburgers's Avatar
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    Magnfication, distance, focal length, numbers, errr...

    Ok, so it turns out I could use some help on my magnification math. It may be "easy" as I said earlier, but for someone other than me. Basically, I'm not sure what formulas to use.

    I need to make an object that is X mm in size (.05mm let's say, for now) appear as Y mm (.005-.01mm in this case) on the film. I have a 180mm lens. At what distance do I need to have my lens at to achieve this?

    Thanks in advance!

    update..... 1/f = 1/u + 1/v
    magnfication... M = v/u

    f is focal length, u is subject distance, v is lens to film distance

    Is this all I need? This is embarassing, I mean, I supposedly passed calculus! You would think that this simple algebra would be a breeze...
    Last edited by holmburgers; 06-01-2010 at 12:45 PM. Click to view previous post history.

  2. #72
    holmburgers's Avatar
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    I've realized that my discussion really doesn't belong in this thread, which should be preserved as a discussion of the historical autochrome and not my experiments with RGB-colored screens. I'm gonna make a new thread to discuss this, sorry for hijacking!!

    cheers!

  3. #73

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    Problems with the Met's Research on logivity of autochromes?

    The Metropolitan Museum's research indicates an extremely short life for autochromes on exhibition unless put in a low-oxygen environment during display. It's causing most institutions to determine that they should never procure or show autochromes, because they do not have that ability. But in my experience, autochromes have been relatively stable, especially when kept away from direct heat. I suspect it was their researcher Luisa Casella's method in creating "new" autochromes that caused this dye instability, since she didn't actually test historical autochromes themselves. Any one have any ideas on how stable or unstable actual historical autochromes are. I've yet to see fading in any and I've seen thousands.
    Alex

  4. #74
    Photo Engineer's Avatar
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    I have a box of Autocrhome stero plates from nearly 100 years ago that look just fine.

    They are kept in the original box. IDK how they were kept before I acquired them though.

    PE

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    On the Metropolitan Museum of Art’s Research and the longevity of Autochromes

    This is in reply to Alex Novak’s March, 2012 posting "Problems with the Met's Research on longevity of Autochromes?"

    This reply is not intended as in-depth refutation. Nor should it be read as criticism of Alex Novak’s post, which no doubt accurately reflects what has been reported to Mr. Novak.

    It has been standard museum practice since the early 1980’s not to display original Autochromes, primarily due to the fear of fading. Facsimiles, whether printed on paper or on translucent material have usually been put on display in place of originals. The research conducted by Luisa Casella was designed to learn whether it would be possible to display original Autochromes, if they were placed inside of oxygen-free environments. It was hoped that these anoxic enclosures would permit museums and other institutions to display original Autochromes from their collections. It is important to note that the creation of anoxic environments applies only for the continuous display of Autochromes, but not for their storage. There is absolutely no reason why museums, curators, and collectors should not continue to procure Autochromes for their collections and to view and to marvel at their unique and enchanting beauty.

    A question regarding Ms. Casella’s methodology has been raised. While the design and parameters of the research are too complex to summarize in a few sentences, it is a fact that the experiments did indeed include historical samples of exposed and developed Autochrome plates as well as previously unexposed and undeveloped plates plus the dye samples created using the historic Lumiere formula. Unexposed and undeveloped Autochrome samples dating from 1908, 1910, 1912 and 1920 were tested.

    Two other points should be noted: 1). The results observed and reported by Liusa Casella are based on an exposure period that can be considered the equivalent of displaying an Autochrome in a common light box, emitting 2000 lux, for 9 hours a day over a period of approximately 14 months. 2). It is important to note that the term fading only applies to the color dyes, not to the image itself. There may be some confusion if one considers fading as one does with an albumen photograph. Autochromes do not appear “lighter” as the color dyes fade; rather, the change is in the direction of a shift in the colorcast, usually toward a yellow/green cast.

    As Alex Novak notes, Autochromes are indeed stable if kept in optimum temperature and humidity conditions, and protected from long-term exposure to light. The only thing required for their long-term preservation is a common sense approach. In addition to light, Autochrome plates are sensitive to moisture and heat. Prolonged exposure to light will cause the dyes in the color screen to fade; excessive moisture or humidity may cause the dyes to dissolve or migrate; and heat will cause cracking in the image layer. Thus, long-term storage requirements are no different for Autochromes than for any light-sensitive material. When Autochromes are not being viewed, they are best stored in light tight box or container. Autochromes should never be stored any place where there is excessive humidity or moisture, such as in a hot attic or in a moist basement.

    Finally, it should be noted that due to Ms. Casella’s pioneering work with anoxic environments, the Met was confident enough that it permitted display of several rare and important Autochromes by Alfred Stieglitz and Edward Steichen in a January 2011 exhibition. This allowed these original Autochromes to be viewed and admired by the general public for the first time in several decades.

    For additional information on her publications, please see Lusia Casella's website: http://www.luisacasella.com/?page_id=20

    Mark Jacobs

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