put away your eyeglasses. tele vue`s Dioptrx

put away your eyeglasses. tele vue`s Dioptrx
equipment review
Put away your eyeglasses. Tele Vue’s DioptRx
lenses correct astigmatism. /// BY MIKE d. REYNOLDS
The sharpest image
At last! There’s help for the observer
with astigmatism. For the first time, amateur astronomers
suffering from this malady can cast off their eyeglasses and
observe like the rest of us. • Generally speaking, the ability
to focus a telescope allows observers to correct for nearsightedness and farsightedness. But a
focuser won’t correct another common eye
defect: astigmatism, where light rays focus
at different points, creating a blurred image.
Most people who suffer from this problem
find it intrusive only at low magnifications;
some see its effects at all magnifications.
In the past, some observers have had a
special eyeglass prescription for astigmatism only. Others went to the expense of
having corrector lenses produced for their
telescope to correct for their astigmatism.
Finding a better solution for this inconvenience was Tele Vue’s goal.
DioptRx is a corrector-lens system that
attaches to the top of specific Tele Vue long
eye-relief eyepieces (see table below).
DioptRx-ready
Tele Vue eyepieces
Nagler Type 4 — 12mm, 17mm, 22mm
Nagler Type 5 — 26mm, 31mm
Panoptic — 22mm, 27mm, 35mm,
41mm
Plössl — 32mm, 40mm, 55mm
Radian — 3mm, 4mm, 5mm, 6mm,
8mm, 10mm, 12mm, 14mm, 18mm
74 astronomy
⁄⁄⁄
Because each person suffering from astigmatism has a different prescription (each
eye also can be different), Tele Vue offers
DioptRx corrector lenses in 0.25-diopter
steps from 0.25 diopter up to 2.5 diopter,
and also 3.0 and 3.5-diopter correctors.
If you examine your prescription, you’ll
note a “cylinder” value — plus or minus —
for each eye. For example, my recent eye
exam revealed cylinder values of +1.25 for
my right eye and +0.25 for the left. Because
my right eye is my observing eye, that’s the
DioptRx correction I want — 1.25 diopter.
(Note: Use cylinder values only. Ignore all
“spherical” and “axis” values as well as all
plus and minus signs.)
I tested DioptRx lenses on myself and
on several of my astronomy-lab college students. I was interested in seeing not only
how DioptRx worked for an experienced
observer, but also what difference a novice
at the telescope would see.
For the test, I used various Tele Vue eyepieces and three different telescopes,
including a 3.2-inch Vixen ED80sf apo-
© 2009 Kalmbach Publishing Co. This material may not be reproduced in any form
www.Astronomy.com
OCTOBER 06
without permission from the publisher.
THE 32mm Tele Vue Plössl eyepiece is one of
21 that come “DioptRx-ready” (see list at
left). all photos: astronomy: William zuback
chromatic refractor, an 8-inch Meade
LX200 GPS Schmidt-Cassegrain telescope,
and a Coulter Odyssey 10-inch Newtonian
reflector on a Dobsonian mount. I
observed under dark skies and good conditions, viewing a variety of bright and faint
objects at different magnifications.
T. A. RECTOR AND B. A. WOLPA/NOAO/AURA/NSF
What Is Astigmatism?
Astigmatism is a common condition of
the eye in which the cornea curves
unevenly. (Rather than being round, the
cornea resembles a football.) The root of
the word is Greek, meaning “without”
(“a”) “a point” (“stigma”). The result of
astigmatism is out-of-focus vision along
one axis. Diagnosing astigmatism
requires a standard eye examination
with a refraction test, which also determines if one is nearsighted or farsighted. Once diagnosed, correcting
astigmatism requires glasses or hard
contact lenses; soft contact lenses have
not proved as effective. — M. D. R.
A DioptRx lens fits over the top of an
eyepiece once you remove the original rubber eyeguard and install the DioptRx (and
its eyeguard). Next, you must orient the
corrector lens for your eye by rotating it.
Tele Vue prints letters on the side of each
DioptRx lens so you can return to a certain
alignment. I found it simple enough to turn
the correcting lens until the stars became
sharp. DioptRx is easy to use, and when
others not suffering from the same amount
of astigmatism as you want to look through
your telescope, it’s easy to remove, too.
I was impressed with how much better
images appeared through all three telescopes and eyepiece combinations with the
DioptRx lens installed. For me, this worked
especially well at low magnifications. (I
don’t have issues with astigmatism at higher
magnifications.) Stars were sharp to the
edge of the field of view in all eyepieces.
Mike D. Reynolds — the Dean of Mathematics
and Science at Florida Community College
— wears glasses for nearsightedness and suffers
from astigmatism.
Because I teach college astronomy
courses, I was interested in my students’
reactions to DioptRx. In order to participate, I asked each student suffering from
astigmatism to provide a recent eye prescription to verify their cylinder values. I
asked the five students to note how the
objects appeared once they focused the
telescope. For this test I used only the 8inch Meade Schmidt Cassegrain because it
was motor-driven. I didn’t want the stu-
⁄⁄⁄
s p e c i f i c at i o n s
Tele Vue DioptRx
Range: 0.25 to 2.5 diopters in 0.25 diopter steps, in addition to 3.0 and
3.5 diopters
Lenses: multicoated glass in anodized aluminum housings with rubber
eyeguards
Also: rotatable for fine-tuning with
engraved lettering for setting
reproducibility
Street price: $98
Contact information:
Tele Vue Optics
32 Elkay Drive
Chester, NY 10918
[t] 845.469.4551
[w] www.televue.com
dents to be concerned about adjusting the
telescope during their observations.
All five saw better with their DioptRx
lenses. I asked each — observing separately
so they could not influence each other —
what he or she saw and how it changed
with the DioptRx. Two students were more
specific: They saw increased detail when
observing the Moon and Saturn at higher
magnifications. I continue to collect student data to see if Tele Vue has found that
“missing link” for those who report having
a poor experience at the eyepiece.
I’m convinced Tele Vue’s DioptRx will
help those who suffer from astigmatism
and hate wearing glasses while observing.
At a street price of around $98 per corrector lens, it won’t empty their savings. And
for those who use only one eye to observe,
one corrector lens is sufficient. Imagine
that — twice the vision at half the price.
At first, I was skeptical Tele Vue’s DioptRx would make a difference. When I used
this amazing lens, however, I gasped so
loud friends came over to see if
something was wrong. I
replied, “No, I’ve just
got my sharp vision
back. Now, I can throw
away these glasses!”
www.astronomy.com
75
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