By PJ Anway
Figure 1. (Presented with permission of
The Telementor refractor is a telescope that many amateur
observers have heard about, but relatively few have actually owned. It
has a well-deserved reputation for being a quality refractor and that
is not surprising, due to its pedigree - Carl Zeiss. Zeiss is known for
producing quality instruments in almost every field involving lenses. I
have owned five different Zeiss Telementors over the years and have not
been disappointed by the performance of any one of them.
My reason for writing this article is because the Telementor
is relatively rare in the US and this has resulted in a bit of
misunderstanding of the different models and their features. For
instance, recently, on one Internet auction site, a well-known and
experienced telescope dealer had to pull his ad for the sale of a Zeiss
Telementor on three different occasions. The reason? He kept misstating
information about which model he was actually selling. After that, I
thought an article might be of help. Let me start with a little history.
In a way, the Telementor got its start in 1949 in Germany. In
that year, its predecessor, the AS 63/840 refractor, was first
produced. The "AS" stands for ""Astro-Spezialobjektiv" or
"Astro-Special" Objective. Though considered an achromat, the "special"
part of the AS objective came from the Steinheil design lens with a
KzFN2/BK7 lens configuration. The Zeiss AS lens is a "flint-leading"
doublet using the KzFN2 ''short flint". By using this lens design, the
chromatic aberration (color error) is helped somewhat. In his landmark
article in Applied Optics (entitled "Planetary Telescopes"), James G.
Baker termed the Zeiss AS lens a "semi-apochromat". I have owned one of
these scopes and I felt it did show some improvement in color
correction over the traditional achromat. The AS 63/840 was advertised
as the "school and amateur scope" but this is not the telescope
referred to when we speak of the Telementor. That scope would not be
seen on the market until the 1970's.
The Carl Zeiss Jena refractor that came to known as the
"Telementor" would make its appearance around May of 1972. It was
produced with the idea of placing one in every secondary school in the
Republic of Germany, thus the title - "School scope" or "Telementor".
This version of the refractor would be a completely revised edition
from the AS63. It would house a typical Fraunhofer design doublet
objective - an achromat consisting of crown-flint lens elements BK7/F2.
It would also be a much more compact cell design than that of the AS
lens and Zeiss would be give it the designation "C63/840".
Obviously, objective would also have a diameter of 63mm and a
focal length of 840mm (f/13.3). Even though this lens is inferior to
the AS lens as far as color correction, maintaining the long focal
ratio of f/13 would enable the Telementor to show only a small amount
of chromatic aberration on bright objects. As with all Zeiss lenses the
excellent figure and polish makes it a great performer. The lens I have
in my Telementor gives sharp views with excellent contrast and allows
for magnification exceeding 80x per inch.
Over the years the Telementor has been basically the same
telescope built in 1972, with just a couple of changes to the body of
- The Telementor-I came with a helical rear focuser. The
Telementor-II and Telemator came with an internal focusing system (I'll
discuss the focusers later).
- The Telementor-I and Telementor-II did not come with a
finder scope. The Telemator was equipped with a 7.5 x 42 finder scope.
- The Telementor-I and Telementor-II came on the standard
equatorial “T-mount”; the manual mount pictured above. The Telemator
came on a motorized “TM-mount”.
- The exception to these rules came with the last
installment of the Telementor in 1995, which marketed as the “C63/840”
and came with a finder scope and gave the purchaser the choice of a “T”
or “TM” mount. It is the scope pictured above.
Now for the features that all Zeiss Telementors and Telemators
- the C63/840 lens and cell
- the one-piece tube that extends a few inches beyond the
lens cell forming a dew shield
- the "sighting device"
- the M44 rear threads
- the dovetail bar
Let's look at each of these on the Telementor-I that I
Figure 2. My Telementor-I on a Zeiss TM
Figure 3. (1) the C63/840 lens and cell
This is the heart of the Telementor, the C63/840 lens and
cell. A cemented doublet achromat, it is nicely tucked into a compact
cell. Though common to all Telementors, it is placed differently into
the OTA's of the Telementor-I and Telemento-II/Telemator. In the
Telementor-I, two small screws inserted into the OTA hold the cell in
place. It can be removed for cleaning, but is somewhat tricky to
reinstall. In the Telementor II the lens cell is screwed onto an inner
tube (more on that later). The label is the famous Zeiss Jena logo –
with the name “Carl Zeiss Jena” in an achromat doublet lens outline.
Figure 4. (2) an OTA that extends a few
inches beyond the lens cell forming a dew shield
The OTA for the Telementor-I extends about 3-1/2" beyond the
lens cell forming in effect a dew shield. This makes for a classic look
that appeals to me, but without a sliding dew-shield, it does not allow
any shortening of the tube for travel.
Figure 5. (3) the "sighting device"
All Telementor OTA's have two small "peep holes" on the top of
the OTA. When aligned by sight, the tiny section of sky seen through
these is where the OTA is pointing. These are surprisingly effective in
accurately pointing the refractor, in my opinion as good as red dot
finder. The one drawback to them is that under very dark skies, the
front sight can be difficult to see.
Figure 6. (4) the M44 rear threads
Zeiss maintained a unique way of attaching accessories to
their refractors. It is called the M44 thread. M44 comes from the fact
that the diameter of the thread is 44mm.
All of the Telementors (as well as many AS and APQ scopes) use
this thread to mount just about everything - including:
Figure 7. Zenith prism diagonals and
Figure 8. Barlows
Figure 9. Extensions in lengths of 20mm to
Figure 10. Eyepiece adapters
Zeiss made a .965" eyepiece adapter (right) for the Carl Zeiss
Jena .965" ortho and mono eyepieces. Also, many after-market eyepiece
adapters were later made for 1.25" and 2" eyepieces. All attached using
Changing from one threaded accessory to another at times can
be a pain, when it requires you to unscrew one accessory and screw in
another. To alleviate this somewhat, Zeiss (and several after-market
suppliers) came up with "quick-change" adapters. These make changing
accessories much easier. It also doubles nicely as a camera angle
Figure 12. Here is pic of the changer in
Figure 13. (5) dovetail bar
Most Zeiss refractors have a dovetail bar bolted to the bottom
of the OTA. These vary in length depending on the scope, but are
consistent in width and angle. The Telementor dovetail is 9” long by
1-3/8” wide. It also has pin at each end to prevent the scope from
accidentally slipping from the mount clamp in the dark.
(An additional note: Astro-Physics makes a dovetail clamp
(DOVE08) that fits the Zeiss dovetail perfectly. This makes it possible
to use Zeiss refractors on other non-Zeiss mounts.)
That covers the similarities of the Zeiss Telementor design. Let’s next take a look at the main difference, the focusing mechanism.
The Telementor-I uses a helical focuser at the rear of the
OTA. It is a little over 2-1/2” (65mm) in diameter and has a travel of
1-3/8” (35mm). I personally love this design. The one on my
Telementor-I is very smooth and brings all my eyepieces to focus.
Though I am sure there are eyepieces out there that the 35mm of
back-focus might not accommodate.
With the Telementor-II and Telemator, Zeiss removed the
helical focuser. In fact they did away with a rear focuser altogether
and replaced it with a very unique design.
The diagonal (and therefore eyepiece) is screwed to the rear
of the OTA. It remains stationary, while the objective is moved back
and forth to obtain focus. A second tube inside the OTA accomplishes
this. The objective cell it attached (screwed) to the front of this
internal tube and a knob on the side of the OTA moves the internal tube
along slides located between it and the OTA. This focusing system works
very well and is also smooth, allowing close to 100mm of travel.
Most used Telementors sold today are of this variety.
Below are pictures of the Telementor-II and Telemator for
comparison. In it you see the focusing knob that moves the inner tube
(and objective) on the side of each OTA.
Figure 16. (Presented with permission of
The features of each refractor are noted in this ad from the
Figure 17. (Presented with permission of
Seiler Instrument and Manufacturing Inc.)
Some additional notes about the mounts:
- The T-mount is a manual equatorial mount, with slow-motion
knobs. These can be turned to track the scope for about 30 minutes.
After that, they have to be reset by loosing another locking knob.
- The TM-mount: tracks automatically with a motor. However, the
motor that drives the mount is the European 220v 50hz power standard
and will not track correctly on the US 60hz power standard. You have to
purchase a voltage converter to use it in the US.
The last note is about labeling. Zeiss did not label the
Telementor OTA for years. Most have no labels, but it isn’t hard to
recognize the unique look. However, I have seen a couple of labels from
OTA produced in the 1990’s. The first is the label from a Telementor II
I used to own.
I contacted Dr. Wolfgang Wimmer from Zeiss about this label
and he dated its use to 1990 and 1991. The only other label I have seen
is the “Zeiss Germany” in the box pictured on the brochure pictures
The Telementor is a unique refractor that beckons back to days
of old, when a “60-something”mm refractor was a common choice of many
amateur astronomers. It is still a wonderful instrument that works very
well for the moon, planets and double stars, my main targets. It has
also achieved a following that is well deserved. In a tongue-in-cheek
article by Jay Freeman entitled: “You know you are a planetary observer
when...”, one of the lines states: “You know you are a planetary
observer when, you actually own a Zeiss Telementor”……… enough said.