Astro-Tech Dielectric Diagonals.

This 1.25” Astro-Tech diagonal has state-of-the-art 46-layer dielectric mirror coatings for a full
99% reflectivity. In addition to higher reflectivity than the 88% of a conventional aluminum
diagonal or the 96-97% of an easily-tarnished silver diagonal, the durable ion-deposited
dielectric coatings on the mirror’s finely-polished 1/10th wave BK7 optical glass substrate
also provide higher contrast and resolution during critical planetary, lunar, and binary star
observations.

The mirror housing is precision-machined from solid aluminum, rather than simply flimsy
plastic or a sheet metal stamping, as you’ll find with ordinary diagonals. A rigid die-cast
metal U-shaped backplate with stainless steel hardware holds the mirror in perfect optical
alignment in the machined body. The solidity of the construction is mirrored in the diagonal’s
substantial 7 ounce weight. In addition to being anodized an antireflective matte black, the
interior of the body is lined with light absorbing materials. The focuser-side barrel is also
anodized antireflective matte black, and is internally antireflection threaded for even higher
contrast. The barrel is threaded to accept standard 1.25” filters. The stop at the bottom of the
1.25” eyepiece holder that prevents eyepieces from hitting the first surface mirror may slightly
vignette the image of a very wide field 40mm eyepiece. Shorter focal length eyepieces are
generally unaffected.

The 1.25” eyepiece holder uses a non-marring soft brass compression ring to clamp
eyepieces in place, rather than a thumbscrew that can scratch an eyepiece barrel by
tightening down on it directly. The knurled and chromed thumbscrew that operates the
compression ring is a full 1/2” in diameter, twice that of many competitive diagonals. This
provides a sure grip in cold weather when wearing gloves or mittens.

A slanted groove cut into the outside of the focuser-side barrel engages with the telescope’s
visual back or eyepiece holder thumbscrew to act as a safety stop. This keeps the diagonal
from falling should the scope’s thumbscrew loosen slightly from cold or use. Dust covers are
provided for both sides of the diagonal.

This premium 1.25” diagonal works with virtually any Schmidt-Cassegrain, Maksutov-
Cassegrain, or refractor that uses a 1.25” star diagonal. The Celestron NexStar 8i Special
Edition is the only known exception. Due to the short fork arm of this scope and the length of
its 1.25” visual back, this diagonal will not clear the drive base when the NexStar 8i is pointed
at the zenith. For all other scopes, the Astro-Tech diagonal provides a visible improvement. It
gives you all the visual performance your scope is capable of delivering, at a price that’s very
affordable.

Price - £51.00

This 2” Astro-Tech first-surface mirror star diagonal has state-of-the-art 46-layer dielectric
mirror coatings for a full 99% reflectivity, higher than the 88% of a conventional aluminum
diagonal or the 96-97% of an easily-tarnished silver diagonal. The durable ion-deposited
dielectric coatings on the mirror’s finely-polished 10mm thick 1/10th wave BK7 optical glass
substrate also provide higher contrast and resolution during critical planetary, lunar, and
binary star observations. This Astro-Tech diagonal is, quite simply, unique among premium-
quality 2” star diagonals for its exceptional value.

The mirror housing is precision-machined from solid aluminum, rather than simply flimsy
plastic or a sheet metal stamping, as you’ll find with ordinary diagonals. A rigid U-shaped die
-cast metal backplate with stainless steel hardware holds the mirror in perfect optical
alignment in the machined body. The solidity of the construction is mirrored in the diagonal’s
substantial 17 ounce weight.

The interior of the body is lined with light absorbing materials, in addition to being anodized
an antireflective matte black. The 2” focuser-side barrel is also anodized antireflective matte
black, and is internally antireflection threaded for even higher contrast. The barrel is threaded
to accept standard 2” filters.

Rather than using a metal thumbscrew that contacts eyepiece barrels directly and can
scratch them, the diagonal’s 2” eyepiece holder uses a non-marring soft brass compression
ring to secure 2” eyepieces and the standard equipment 1.25” eyepiece adapter in place. The
knurled and chromed thumbscrew that operates the compression ring is a full 1/2” in
diameter, twice that of competitive diagonals. This provides a sure grip in cold weather when
wearing gloves or mittens. A slanted groove cut into the outside of the focuser-side 2” barrel
engages with the scope’s focuser drawtube thumbscrew to act as a safety stop. This keeps
the diagonal from falling should the scope’s thumbscrew loosen slightly from cold or use.

The 1.25” eyepiece adapter uses a compression ring to hold the eyepieces in place. The
scope-side barrel of the 1.25” adapter is grooved to keep it from accidentally slipping out of
the 2” diagonal. Dust covers are provided for the 1.25” adapter and the diagonal’s 2” barrel.

This diagonal is a visible improvement over the standard diagonal provided with virtually every
refractor capable of using 2” optics. It can also be used with a Schmidt-Cassegrain or
Maksutov-Cassegrain with a suitable adapter. It is an absolutely premium 2” 99% reflectivity
dielectric star diagonal at a fraction the price of competitive models with equivalent
performance and build quality. If there ever was a bargain in astronomy, this is it.

Price - £99.00

This 2” Astro-Tech first-surface mirror star diagonal for catadioptric telescopes has state-of-
the-art 46-layer dielectric mirror coatings for a full 99% reflectivity, higher than the 88% of a
conventional aluminum diagonal or the 96-97% of an easily-tarnished silver diagonal. The
durable ion-deposited dielectric coatings on the mirror’s finely-polished 10mm thick 1/10th
wave BK7 optical glass substrate also provide higher contrast and resolution during critical
planetary, lunar, and binary star observations. It has a physically short nosepiece and SCT
rear cell attachment ring so it can clear the drive base on your telescope. You don’t have to
buy a special version of the diagonal or special adapters to be sure that it can swing through
your 8” scope’s fork arms, as you do with some competitive diagonals. This Astro-Tech
diagonal is, quite simply, unique among premium-quality 2” SCT star diagonals for its
exceptional value.

The SCT rear cell attachment ring will thread directly onto Celestron SCT rear cells and onto
the rear cells of those Meade SCTs that do not have the electric microfocuser as standard
equipment, These include older 2080 and 2120 scopes; all LX3, LX5, LX6, and Premier
scopes; all current and past LX90s; and all earlier LX200 scopes that were supplied without
microfocuser. The diagonal will thread onto a microfocuser-equipped scope if you install the
SCT rear cell ring that came with the focuser into the microfocuser’s 2” drawtube. If you want
a diagonal with a 2” barrel that will slip directly into the microfocuser’s 2” drawtube, consider
the Astro-Tech 2” refractor diagonal instead.

The mirror housing is precision-machined from solid aluminum, rather than simply flimsy
plastic or a sheet metal stamping, as you’ll find with ordinary diagonals. A rigid U-shaped die
-cast metal backplate with stainless steel hardware holds the mirror in perfect optical
alignment in the machined body. The solidity of the construction is mirrored in the diagonal’s
substantial 17 ounce weight.

The interior of the body is lined with light absorbing materials, in addition to being anodized
an antireflective matte black. The short nosepiece that holds the rear cell attachment ring is
internally antireflection threaded for high contrast. The attachment ring fits both Celestron and
Meade rear cells. It is knurled for a sure grip so it can be easily loosened, even when wearing
gloves, allowing you to rotate the diagonal to the most comfortable observing position.

Rather than using a metal thumbscrew that contacts eyepiece barrels directly and can
scratch them, the diagonal’s 2” eyepiece holder uses a non-marring soft brass compression
ring to firmly hold 2” eyepieces and the standard equipment 1.25” eyepiece adapter. The
knurled chrome thumbscrew that operates the compression ring is a full 1/2” in diameter,
twice that of competitive diagonals. This provides a sure grip in cold weather when wearing
gloves or mittens.

The 1.25” eyepiece adapter also uses a compression ring to hold eyepieces in place. The
1.25” adapter has a slanted groove cut into the outside of its focuser-side 2” barrel. This
engages with the diagonal’s compression ring to act as a safety stop to keep the adapter
from accidentally slipping out of the 2” diagonal should the compression ring loosen during
use. Dust covers are provided for the 1.25” adapter and the diagonal’s SCT attachment ring.

This diagonal is a visible improvement over the standard 1.25” prism diagonal provided with
virtually every Schmidt-Cassegrain or Maksutov-Cassegrain telescope. It is an absolutely top
-rank 2” 99% reflectivity dielectric star diagonal at only a fraction the price of competitive
models with equivalent performance and build quality. If there ever was a bargain in SCT
astronomy, this is it.

Price - £99.00

The Astronomy Shop

1 Tone Hill. Wellington

Somerset TA21 0AU

United Kingdom

Telephone: +44 (0)1823 665510