Type E objective
E objective was the first standard for amateur
telescope manufactured by Carl Zeiss Jena before WWII (probably from 1897).
The 1899 “Astro 1” English catalog (Carl Zeiss Jena, 1899) list it as “E Astronomical Telescope Object-Glasses”
(Made of ordinary silicate glasses). As reported in the Zeiss Historica paper
on this catalog (Grossman, 1990), these objectives are based on the
classical Fraunhofer formula and are the objectives most commonly encountered
by collectors today. This is also a type of objective commonly used in large
professional instruments like the 300 mm Griffith telescope and the 250 mm
Franklin Institute. Accordingly Grossman sizes were from 20 mm to 500 mm, with
larger sizes on special order.
The 1906 catalog “Astro 8” (Carl Zeiss Jena, 1906) listed three
objective types only: the “E”, “A” and “B” objectives. The “E” are described as
“standard, two glasses” and “cut in standard glasses”. Sizes varies between 60
mm (f=60-75 cm) and 200 mm (f=280-320), so focal ratio between F/10 and F/12,5
for smaller diameters and F/14 and F/16 for the biggest one.
Catalog Astro 30 of 1916 (Carl Zeiss Jena, 1916) list “E” objectives
as F/15 with a Fraunhofer design, so the 60 mm diameter lens had a focal length
of 85 mm. Many of the 60 mm lenses now in the hands of collectors have this focal
length. In this catalog a 80/1200 mm “E” lens is listed, as others in different
size (110, 130, 150, 200, 250, 300, 400, 500 mm diameter).
The "E" objectives could be had in either
standard Steinheil flint-forward design or Fraunhofer crown-forward design, on
special order. Both were 850 mm focal length (Cloudynights, 2010) – probably referring
to 60 mm diameter objectives.
The "E" design disappeared in amateur
telescopes after WW2, and was replaced by the "AS" together with the
"C", a cemented achromat (see later); the "E" design did
live on after WW2, but only in large, professional scopes, where apochromats
were too expensive (Cloudynights, 2010).
A Brazilian firm, DFV, produced in the ‘70s some
number (maybe 40) of small 63 mm diameter refractors with stock “E” objectives,
very rare today (Note: t.b.c.). See Oliveira in (Cloudynights, 2010) and a selling advertisement on a
Brazilian site (Preciolandia, 2014).
Type A objective
According to Cloudynights (Cloudynights, 2010), from around 1897 you could get a
doublet "A" semiapochromat, with three times better color correction
than a normal "E" objective.
The "A" had a longer focal length than E
objectives, 1050 mm (with 63 mm in diameter, so F=16,7). From 1926, the
"A" was replaced with the "AS" semiapochromat, which didn't
offer an improvement in performance (more the opposite, by having a bit worse
color correction), but was much cheaper to produce. It also had 850 mm focal
length (for 63 mm diam.), to make upgrades easy.
Neil English book (English) states that “B” was
the first, and then “was followed soon after by a full Apo lens, dubbed the ‘A’
objective, but the glass was apparently unstable and tended to accumulate large
amounts of fungus. Indeed some have speculated that is doubtful whether any
useable ‘A’ objectives are still in existence”.
I have information on at least some A objective
survived.
One
was sold by APM on Astromart in November 2005. The objective (serial n. 11396)
is 150/2670 mm with a focal ratio of 17,8. The announcement gave information on
interferometer analysis, too, with a Strehl ratio of 0.971 and a RMS of 17.9
nm.
Another
“A” is owned by an amateur astronomer in Denmark (“Astrojensen”), it is an A
85/1600, having so a f/18,8. This is pictured in many posts on Astromart (the
scope, not the objective), and probably is dated to 1903. Number on the lens is
1022, on the focuser 5066. The owner speak about another “A” now at Copenaghen
University, of 90 mm diameter.
Another
“pseudo” A objective is documented on Cloudynights: it seems that first AS
objectives were sold in 1924 with the same cell and engraving of the A
objective, modified with an obviously added “S” after the “A” writing. This is
the case of this A(S) 80/1200 n. 13865 described – and pictured - on CN. See
later chapter on AS objective.
Type B (Apo triplet)
objective
Neil English’s book (English) says that “Zeiss
first introduced their so-called semi-apochromatic ‘B’ objective”, and that
“the ‘B’ objective came in focal lengths of between f/11 and F/19. Indeed, the
longer focal lengths were considered to be fully apochromatic”.
Cloudynights (Cloudynights, 2010) says that from 1902 or 1903, you could
get a "B" triplet apochromat, which had twice as good correction of
the "A" objective, IE, six times better than a normal "E"
achromat. The early "B" triplets could be ordered between f/12 and
f/18, but was later standardized to have the same 850mm focal length (f/14) as
the "E" achromats, to enable easy upgrades by simply changing the
objectives (Cloudynights, 2010).
Busch (Busch, 2008) in his detailed
paper on B-objective, mention as first B-Objective the n.606 from 1903, a B
80/1200.
B objective was a apo triplet, well described and
pictured in Astro 8 catalog. Different documented B diameters and focals are as
follows:
B 80 (?)/1110 - f/13,9 (?)
B 80/1200 - f/15
B 110/1620 – f/14,7
B 130/1940 – f/14,9
B 150/2250 – f/15
B 180/3310 – f/18,4
B 200/3000 – f/15
Type AS objective
As written on a post on Cloudynights (Cloudynights, 2010), the A objectives
being around f/17 required longer, and thus heavier, tubes and boxes than both
the B and E objectives which were both generally f/15. In the ‘20s Zeiss
decided that it would be more practical for both them and the customer if the A
objective was f/15. They wanted both the boxes and tubes to be the same with
all three objectives. They could not accomplish this with standard A curves, so
they developed the AS objective we know today, However, they were not sure that
the public would accept and buy them, so they made and sold several "short
focus" A objectives to test the market. These were produced around 1924
and even though they were labeled as A`s, they were in fact AS objectives. Zeiss after about a year or so, determined
that they could safely replace the A objectives with the AS. They added the
letter S to the "A" objectives they had and when these were sold,
they labeled AS objectives as AS. The 80mm f/15 AS of the above mentioned
post’s Author is from the original bunch that was labeled A at first. One can
definitely tell that the S was stamped into the cell at a different (presumably
later) time than the A.
Type “C” objective
In the 1899 catalog these objectives are described as
“… made from heavy but permanent Jena glasses… but not free from secondary
spectrum”. The apertures are from 60 to 200 mm (Grossman, 1990).
A more detailed description of “C” objectives is
provided by Astro 30 catalog. These objectives are named “Two-lens Telescope
Objectives of greater aperture ratio” and described as follow: “The C
Objectives take the place of the E Objectives where a short tube length and
great light-transmitting power are the qualities which are primarily needed, as
in the case of star and comet finders and terrestrial telescopes. The chromatic
and spherical corrections are not equal to those of the E Objectives in view of
the greater aperture ratio. Since, however, the C Objectives are used under
conditions of lower magnifications the residual defects affect the image in a
scarcely appreciable degree”. Aperture were available in 25, 30 and 45 mm with
a 1/8 focal ratio, 60 mm F/5, 80 mm F/8, and 110 and 130 mm F/12 ratio. I
didn’t find any documented example of these earlier C objectives.
After WWII C objectives were made available both
cemented (C50/540, C63/840) and air-spaced (C80/500 and C110/750
“Kometensucher” – Comet Catcher), and were made famous after the ‘70s by the
“Telementor” telescope that is probably the most widespread Carl Zeiss Jena
astronomical instrument in the World. Before ‘70s the near identical “School
and Amateurfernrohr” was equipped by an AS 63/840 lens.
A C 250/1620 (F/6,5) “Kometensucher” is present in
Archenhold Sternwarte in Berlin (Archenhold Sternwarte, 2009).
Other pre-WWII Objective
designs (D, F, G, H)
Astro 1 catalog, as reported by Grossman (Grossman, 1990), listed also other Objective designs
(D, F, G, H), but the only prewar
objectives the author has actually seen or is aware of are types “A”, “B” and
“E” used as primary telescope lenses, and the type “C” used on smaller
auxiliary finder telescopes. According Grossman:
Type “D” were Triple Telescope Object-Glasses, with large flat
field, large aperture than series “F” but not free of secondary spectrum. Sizes
from 20 mm to 150 mm. See later, too.
Type “F” were Telescope Object-Glasses, made of ordinary crown
and flint lenses and the lens elements were cemented together (against the
air-spaced “B” objective). Sizes from 40 mm to 120 mm.
Type “G” were Long Focus Apochromatic Aplanatic
Objecct-glasses (Dr. Harting’s formula for celestial photograph). Sizes from 60
mm to 180 mm.
Type “H” were Short Focus Object-Glasses of large aperture
adapted for celestial photography. Based on the Petzval anastigmat and Planar
lens formulae.
Other later catalogues listed Petzval type astro
lenses.
Type “D” Objective
In 1916’s Astro 30 catalog a “D” Objective is listed,
named as “Three-lens Telescope Objectives of greater aperture ratio”. Description
says “D Objectives are used for similar purpose as the C Objectives that is, in
all cases where it is a material advantage to work with large apertures and
correspondingly great aperture ratios. The optical proprierties, notably the
chromatic and spherical corrections, surpass those realized in the C
Objectives”. Only one focal length is listed, 200 mm aperture, 133 cm focal
length. This seems to come from Tokyo Observatory.
An example (unique?) of this objective on a very
interesting Japanese site (Nifty, 2013), describing this
very special lens and his restoration. Japanese language it is not easy to
understand, but this is clearly a “D” comet finder triplet lens. The author
clearly describes this as a “D” lens from the Astro 30 catalog, used in the 200
mm “Kometensucher” described in same catalog. At the moment, this is the only
one of this kind found from any source of information.
Type APQ Objective
Near the end of the experience of Carl Zeiss Jena
Astronomical Department and in the short time of the new unified Carl Zeiss before the end of production of amateur
astronomer’s telescopes by the German firm in fall 1995 a new gem was born: the
“fluorite” APQ Objectives.
APQ 80/500 – f/6,3 (only 2 produced)
APQ 100/1000 – f/10
APQ 100/640 – f/6,4
APQ 105/800 – f/7,6 (Fluorid-Apochromat,
pre-production, very few units, one marked APQ 105/800 with serial n. 011)
APQ 130/1000 – f/7,7
APQ 150/1200 – f/8,0
APQ 200/2000 – f/10,0 (Very few – maybe three units)
Late Zeiss production and
essays: Presto ED, AQ, AP, CQ
In the world of the Zeiss collectors we can find some
rare information about some very late experimental and pre-series production
objective: the “Presto ED” and the never produced “AQ” (at least one real unit
is known) and AP and CQ.
Presto ED: “only around 30 were ever made and never went into
full production”
