As
an owner of a TSA-102, it was exciting news when Takahashi announced
the second refractor in the “triplet super apochromatic”
series would be a 120mm scope. The TSA-102 has superb optics and
produces high resolution images. The question was, will an increase
of 18mm in aperture make a significant difference and be worth the
cost? The new TSA-120 was introduced in the U.S. at a price of
$3,795 compared to the price of the TSA-102 at $2,695. This equates
to $1,100 for the additional 0.71 inch of aperture that gives a 38%
increase in light grasp. However, Takahashi has included a new
accessory with the TSA-120. It is the Micro Edge Focuser 3, or MEF-3
with a 7:1 ratio for fine focusing. This is an essential accessory
for Takahashi scopes that have a critical focus that is like the tip
of a well sharpened pencil. One can mentally adjust the price of the
TSA-120 to take this new accessory into account. Like the TSA-102
package, Takahashi included Brian Feldman’s quick release
bracket for a finder scope. This BT Technologies QRB has gained
almost universal acceptance among Tak scope owners and is another
essential accessory if you store your scope in a case, either hard or
soft.
The
MEF-3 does have a different feel, one that has been described as
“click-stops.” Those who find it annoying have the
option of installing Starlight Instrument’s Feather-touch 10:1
focuser, albeit at consider-able additional cost.
When
you order a new Takahashi through your favorite dealer, they
routinely contact Texas Nautical Repair in Houston and make
arrangements for delivery. This is noteworthy because Takahashi has
a policy MEF-3
on the TSA-120 2.7 inch focuser
of
shipping by “second day air” as a condition of their five
year warranty. This cost varies depending on how far you live from
TNR. The scope is shipped in Takahashi’s traditional triple
boxes which provide adequate protection from puncture and short
drops. This packaging has become more important because the new lens
cell for the triplets is not readily removed nor can the lens be
easily collimated since the alignment screws have been deleted from
the design. TSA scopes that require collimation need to be returned
to TNR.
The
TSA triplet lenses are air-spaced and utilize S-FPL53 extra low
dispersion (ED) glass in the core lens. The ED glass likely comes
from Ohara in Japan. This triplet lens is heavy. When you lift the
scope, you immediately notice the front end being heavier than the FS
series. When the scope is mounted, it must be moved back further
than the fluorite doublets to achieve balance. The air-spaced lens
has introduced another consideration for owners when they clean the
objective. Fred Garcia of TNR has added to the instruction packet
his notes on cleaning these lenses. It is very important that any
cleaning solution or water not be allowed to seep under the rim of
the lens cell. It is possible for the solution or water to be drawn
between the glass lenses by capillary action. As Fred notes, this
requires shipment back to Japan for repair. I have not read or heard
a similar caution for the air-spaced Christen triplets. Oil-spaced
triplets may not be vulnerable to this damage, but the caution is
important to note. Another consequence of the mass of the glass in
the objective is the increase in time required for thermal
equilibration compared to the fluorite doublets. I typically allow
30 to 60 minutes depending on the temperature difference between
indoors and outdoors or the rate of change in temperature outdoors.
Triple
boxing typical of Takahashi shipping
One
of the improvements of the new TSA design is better color correction.
Even though the Takahashi fluorite doublets provide excellent
images, some have complained about residual color on very bright
objects such as the limb of a crescent moon, Venus, and Vega. This
has been removed with the new lens design. Takahashi advertises this
design as also being much improved for CCD photography. I cannot
comment on this, but certainly there is no observable color on the
aforementioned bright objects. In my research on the TSA design, I
found color curves and spot diagrams that compare the triplet lenses
with the fluorite doublets
(.http://www.takahashi-europe.com/en/TSA-102.optics.php). Both
measurements indicate improvements in the new design. Note that the
TSA lens gives much tighter spots towards the blue end of the
spectrum while the FS lens has tighter spots at the red end of the
spectrum. This pattern and size of spots would imply that one might
want to star test the TSA on a blue star (e.g., Vega) and the FS on a
red star (e.g., Arcturus, Betelgeuse) for best results. Some people
have commented that Takahashi is moving away from fluorite doublets
(the FS series) because of the difficulty of working with fluorite
crystals and the cost of their manufacture. This may be true, but
the move also comes with improvements in the optical performance of
their telescopes. It is interesting that the element fluorine still
finds its way into ED optical glass, only 20 to 30% is in the form of
calcium fluorite (CaF2),
other forms are fluorides of aluminum, strontium, barium and yttrium
(http://www.oharacorp.com/pdf/msds-s-fpl53.pdf). This can be seen by
reading the material safety data sheet for S-FPL53 glass (which is
made available in the workplace where this glass is ground and
polished).
One
of the advantages of the TSA-120 is that it is relatively short
compared to the FS-128 and not much larger than the TSA-102. In the
photo of the three telescopes, the largest is the FS-128 and smallest
is the FS-102NSV (almost identical in size to the TSA-102). The
TSA-120 will fit in the Tenba case designed for the FS-102 (with the
non-retractable, fixed dewshield). Clearly, the sliding dewshield
contributes most to the shorter length, but Takahashi also shortened
the focal ratio from f/8 to f/7.5 for the TSA-120 compared to the
TSA-102. Nonetheless, when the TSA-120 is ready for viewing, that is
with the dewshield extended and a 2 inch star diagonal installed, it
is a fairly long scope. On smaller mounts, like the Great Polaris
(GP) and even the Great Polaris Deluxe (GPD), the increase in length
of the 120 over the 102 contributes to increase in torque on the
mount head. At 5.7 kg (12.6 lbs), the TSA-120 is within the weight
limit for either mount, 15 and 22 lbs, respectively. The GPD is
probably the more desirable sized mount and should have very sturdy
legs to minimize vibration.
When
my new scope arrived, it was one of those marginal nights when
moisture in the air prevented a full night of viewing. Valley fog is
common during the winter in Davis. Our club’s dark sky
location is snowed-in during the winter, so my options for viewing
were limited. Nonetheless, a backyard look at Capella with a 5mm
Nagler showed a nice compact Airy disk with a very fine ring close to
the disk. While not the brightest star, there was no detectable
color. The diffraction ring on the inside of focus was “textbook”
(i.e., Harold Suiter’s book on “Star Testing Astronomical
Telescopes”). The image on the outside of focus was not as
sharp, but my “floaters” were interfering with making a
good assessment. Jupiter was up, but is low in the sky this time of
year; nevertheless, the image was excellent. The belts were distinct
and showed some detail on their edges. The great “red”
spot was not in view. Jupiter’s moons where small compact
spheres. The Double Cluster through a 24mm Panoptic was beautiful,
one of my favorite views. I particularly enjoy trying to see the
faintest stars possible in this object. Likewise, the Pleiades were
beautiful, but because of the high moisture content of the air, I
could not see any nebulosity. By the time I wanted to view M-42 in
Orion, my scope and mount were wet from dew and I decided to bring my
new toy indoors. I will add a more comprehensive observing report to
this review when the weather and sky conditions allow. This review
was truly written on a cloudy night!
Ample
knife edge baffling is retained in the TSA-120
For
those who especially enjoy planetary viewing, Takahashi has designed
an “extender” for the 120. The new extender is the
ED1.5X, which increases the focal length to 1,350mm. The Extender Q
at 1.6X has been used with fluorite doublets and the Petzval design,
e.g., the Sky-90 to reduce residual color. While not considered a
barlow by Takahashi, it does indeed improve planetary images. I look
forward to trying the new ED1.5X.
At
this point, I am pleased with the TSA-120. It has met my
expectations for quality and I suspect it will do the same for
performance. I believe Takahashi has another winner in its stable of
fine astronomical instruments.
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