[LargeFormat] aero ektar

[Richard Knoppow]

----- Original Message ----- 
From: "Clive Warren" <cocam@blueyonder.co.uk>
To: <largeformat@f32.net>
Sent: Tuesday, July 29, 2003 10:28 AM
Subject: Re: [LargeFormat] aero ektar


> At 8:36 am -0700 29/7/03, Richard Knoppow wrote:
> >----- Original Message -----
> >From: "animal"
> >Sent: Monday, July 28, 2003 11:36 PM
> >
> >>  Hello i,m new here and hope you can answer my
question.I,m
> >looking for test
> >>  data on a 7 inch 2.5 aero ektar lens.I,ve tried to
locate
> >this on the web
> >>  but had no luck so far.
> >  > Thanks,simon jessurun,amsterdam,the netherlands
> >
> We have a resident expert on the Aero Ektar lenses here in
the form
> of Michael Briggs and these lenses have been discussed
here before.
> Simon, have a search through the archives - hit any page
of the
> http://www.f32.net site and put your search term in the
box on the
> top right of the page. The list is searchable from the
search box.

  I drew a blank on MIchael's name at the time or would have
posted his site. Sorry Michael, just a senior type memory.
  BTW, the Thorium in the glass is not, as I have seen
indicated, accidental or an inpurity. There are a number of
formulae for NBS and Kodak rare earth glasses in the patent
literature. Thorium was included in some of them to obtain
certain optical properties. Its radio active nature was
either not known or not appreciated at the time. The
understanding of the long term effects of radiation exposure
really did not occur until after the bombing of Japan. You
may remember a scandal and series of law suits regarding the
health effects of radium poisoning of the women who painted
fluorescent watch and clock dials. These originally
contained a small amount of Radium to excite them in the
dark. These women were taking some of the paint internally
because they wetted the brushes with their tongues. Problems
such as those caused by overexposure to medical X-ray were
also not recognized until sometime later than the Aero Ektar
was made.
  Not all Lanthanum glass contains Thorium and not all
Lanthanum glass is radioactive. This is a good thing because
lots of Lanthanum glass is used in modern lenses. The
advantage of this glass is that it has a high index of
refraction but a relatively low amount of dispersion. This
allows elements to have less curvature than if lower index
glass were used but also allows good color correction. As a
rule the less steep the curvature of the elements in a lens
the less the aberrations. For conventional glass types the
higer the index the greater the dispersion, so a type which
has high index but low dispersion is very useful.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com