Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,957   Posts: 1,586,051   Online: 814
      
Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 22
  1. #11
    MattCarey's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    1,303
    Images
    31
    Quote Originally Posted by Ole
    Lanthanum belongs to a group of elements called "rare earth elements" for historic rason only. They are not particularly rare, nor particularly earthy, but the name seems to have stuck. Most of them are named for Ytterby, a village just outside Stockholm, Sweden (Ytterbium, Yttrium, Terbium, Erbium, Holmium, as well as Scandium)!
    Rare earths are generally found as oxides. As I have heard, "Rare" refers to the fact that it is very hard to separate the metal from the oxygen.

    Rare earths are very heavy atoms. Silicon and oxygen (the main components in glass) are rather light. I suspect that the rare earths increase the refractive index of the glass because of this. I should probably google this before saying something stupid...

    Matt

  2. #12

    Join Date
    Jan 2005
    Location
    Moscow, Russia
    Shooter
    Medium Format
    Posts
    768
    Images
    36
    Quote Originally Posted by rjr
    Zhenya, LZOS lists the J9 as "not available" - did they pull it from production? :-(
    Hi Roman,
    glad to see you here again! On your place I shouldn't believe what LZOS site says - that's exactly the place where the right hand doesn't know what the left one does J9 should be still in production, though they made maybe a million of them already? Anyway, I don't think that they brew glass for their photo lenses now. Maybe in case of J9 and, say, J61 they just assemble whatever they have inherited from USSR past...

    PS. One of my friends who worked at LZOS someday told me that most of the color filters made under the brand of LZOS were in fact made by Pentax - optical glass factory in Izum was unable to output consistent quality, so the glass was imported The only local filters, he say, were the yellow ones, and not always!

  3. #13

    Join Date
    Mar 2005
    Shooter
    35mm
    Posts
    380
    Quite a few of the older Canon rangefinder's use this glass too. No wonder, I've never had children....

    Kiron Kid

  4. #14

    Join Date
    Apr 2003
    Posts
    134
    Many so-called Lanthanum glasses are actually Lanthanum/Thorium glasses. Many of the manufacturers preferred to emphasize the Lanthanum content and downplay the Thorium content. Period literature makes it clear that Thorium was intentionally included for the desirable optical properties of this glass: a high index of refraction with a low dispersion. This helps reduce chromatic and spherical abberations.

    The radioactive lenses that I have measured are much to radioactive to be explained by the extremely slight radioactivity of Lanthanum, or by contamination with Thorium. The amount of Thorium is too large to be contamination.

    Most major lens manufacturers used Thorium glass: Kodak, Voightlander, Schneider, Pentax, Nikon, etc. The Apo-Lanthars definitely contain Thorium. I don't know whether Russian lens manufacturers used thorium glass. One possible sign is that the glass ages to a tea color. This can be cleared via exposure to UV light.

    Thorium glass is no longer used -- optically similar glasses without thorium are available.

    For more on thorium glass, see my Aero-Ektar webpage: http://home.earthlink.net/~michaelbr...aeroektar.html

  5. #15
    Donald Qualls's Avatar
    Join Date
    Jan 2005
    Location
    North Carolina, USA (transplanted from Seattle)
    Shooter
    Multi Format
    Posts
    1,845
    I have one of the radioactive thorium-glass Super Takumar lenses. Aside from yellowing (cause by decay products of the thorium, and I'm told that a few weeks under UV light will correct it -- trying to find an economical way to set that up without exposing the lens to the heat of direct sun), it's an excellent lens indeed - but based on my experience in the last few months, not enough better than my Tessars and Skopars to be worth the risks of grinding the thorium glass or the expense of properly disposing of the radioative and toxic residue.

    As noted above, there are now glasses that effectively duplicate the optical properties of these radioactive glasses without the potential health issues. However, I'm not getting rid of my Super Takumar -- I don't store it in the headboard of my bed, or use it as a loupe, and I don't consider it any more hazardous, when stored with my camera gear and used on the camera as a lens is intended to be used, than ordinary photo chemicals used in their common applications.

    Would I buy another one if it were crystal clear, clean aperture, and otherwise good condition? In a heartbeat, if I could afford one (and I might, before too much longer).
    Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.

  6. #16

    Join Date
    Sep 2002
    Location
    Omaha, Nebraska
    Shooter
    Multi Format
    Posts
    2,512
    Images
    4
    I remeber an article in the old Camera and Darkroom that discussed using a spcecial light to remove "impacted photons" from older lenses. I don't remember if it was specifically discussing lenses containing trace amounts of radioactive elements. I do believe that it was a UV light source. When I get time I will rumage through my stacks and find it.
    "Fundamentally I think we need to rediscover a non-ironic world"
    Robert Adams

  7. #17

    Join Date
    Mar 2005
    Shooter
    Multi Format
    Posts
    3,581
    Um, Jim, I have a small pile of lenses with elements containing Thorium. All had glass yellowed by radiation damage when I got them. The worst of the lot shot distinctly yellow EPP transparencies. Not good. A month or so of basking under a 20w fluorescent BLB tube cleared all of them, including the worst.

  8. #18
    Ole
    Ole is offline
    Ole's Avatar
    Join Date
    Sep 2002
    Location
    Bergen, Norway
    Shooter
    Large Format
    Posts
    9,282
    Blog Entries
    1
    Images
    31
    I rather like the "warm-tone" effect of my APO-Lanthar

    It's weak, and only ovious when compared to the same scene shot with a "normal" lens. Combined with the smooth rendition the lens is (justifiably) famous for, it's a wonderful effect. I only wish I could afford some more of them - say a 210 and a 300mm...
    -- Ole Tjugen, Luddite Elitist
    Norway

  9. #19
    Donald Qualls's Avatar
    Join Date
    Jan 2005
    Location
    North Carolina, USA (transplanted from Seattle)
    Shooter
    Multi Format
    Posts
    1,845
    Unfortunately, my Super Takumar 1.4/50 is yellow enough to give about 1/2 stop filter factor, accentuate clouds, and make color prints look muddy -- I've had to stop using it for color. Gotta get a UV light set up and see if I can clear it...
    Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.

  10. #20
    titrisol's Avatar
    Join Date
    Aug 2004
    Location
    Rotterdam
    Shooter
    Multi Format
    Posts
    1,671
    Images
    8
    Donald, since you are in NC now, sunlight is strong enough this time of the year to leave it near a window and celar it in a couple of days.
    Wrap it in aluminum foil to prevent overheating and use the most of UV
    Mama took my APX away.....

Page 2 of 3 FirstFirst 123 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin