Rodenstock-Ysarex recalculated Tessar design/construction info? (R Knoppow ?)
Murray
I bought a box of several apparently unused Rodenstock-Ysarex 127 mm
f/4.7 front cells.
There are 2 elements in it, the front being a meniscus (concave-front,
concave rear, roughly 45-50 mm f.l.), and the rear element being
double concave (I thought the 'front' of the rear element was planar
but found about 0.025" height with a dial indicator.
Does anyone (Rich Knoppow?) know what elements was in the rear portion
of this lens, and which elements were the porportedly 'hot' glass?
It's supposedly a recalculated Tessar and presumably still has 4
elements in 3 groups.
I am trying to find an experimental use other than replacements for
scratched Polaroid 110B's.
I did unscrew the front cell from a Polaroid Tominon 127 mm f/4.7 and
was able to focus it at (very) approximately the same distance as the
Tominon - very unscientific test, handheld, projecting a light bulb
onto a cinderblock. I was just trying to find SOMETHING it would focus
with.
Thanks
Murray
Richard Knoppow
"Murray" <Mur...@multi-volti.com> wrote in message
news:e7e8187.04031...@posting.google.com...
I haven't been reading the Usenet groups regularly lately
so pardon the delay.
The Ysar and Ysarex are Tessar type lenses. I don't know
the difference between the lenses sold under these two names
other than the Yserex seems to be common on Polaroid cameras
and oscilloscope cameras.
A Tessar has a font element consisting of a nearly
plano-convex lens in the front and a bi- concave in the
rear. The combination has little power and is negative. The
rear element is a bi- concave and bi-convex lens cemented.
Sometimes the surface facing the stop is nearly plano. The
rear has most of the power, the front has most of the
corrections.
If these cells have positive power, that is if they
magnify or can project an image, the lens is NOT a Tessar
but probably a double Gauss of some sort. There are two
types of four-element air-spaced lenses found commonly. One
is the Celor or Dialyte type. This has elements which are
all bi-convex or bi-concave. The outer elements are
bi-convex, the inner ones bi-concave. This is the generic
type of the Apo Artar, Kodak f/7.7, 205mm Ektar or K.A.,
Goerz Dogmar, etc. The other is the double-Gauss type. In
these all the elements are meniscus with the concave
surfaces facing the stop. This is the generic type of the
Kodak Wide Field Ektar and many other medium wide-angle
lenses. Both have been used for general purpose lenses and
for copy lenses. The Dialyte has rather narrow coverage, the
double Gauss rather wide coverage. I think someone on this
group identified the Tominon as a Dyalite not too long ago.
I have no idea of which element(s) might be radioactive.
In any case the radiation from most older Lanthanum glass
elements is very low. The radioactive substance is Thorium.
Thorium was added to the Lanthanum to modify its optical
properties, usually in very small amounts. Some lenses have
been made with significant amounts of Thorium glass, mostly
special purpose military lenses. One needs to take care
about some older aerial mapping lenses, but consumer type
camera lenes are generally not hazardous.
--
---
Richard Knoppow
Los Angeles, CA, USA
dick...@ix.netcom.com
Murray
lens, does this achieve asymmetry, vignetting, or just alter coverage?
Then, if, say a pair of symmetrical menisci are altered to two
different focal lengths, presumably achieving asymmetry does the
longer or shorter f.l. determine where the iris goes?
I downloaded OSLO EDU...I need to figure out how to use it and do some
experiments to start answering my too-many questions.
Thanks
Murray
Murray
I intuitively figured out part of the math for 3 elements and
Primitive Photography (Greene) confirmed what I was missing.
I found a + lens that allowed me to focus an image combining it with
the R-Y front cell. Now for a little re-calculating to see what
working range I can get out of it.
Thanks
Murray