popular Plossl is a perennial pick with astronomers, young and old.
Invented in mid-1800 by G. S. Plossl of Austria, it is one of the
oldest eyepiece designs still readily available. His design, however,
remained obscure for nearly a century, not becoming popular until
around 1960. For this reason some people get the impression that the
Plossl is a more modern design. This somewhat simple design consists
of two achromat doublet lenses or four elements in groups of two, one
pair for the eye lens and one pair for the field lens. This provides
a better corrected image over three-element designs such as the
Kellner. Thus it works better in fast telescope optics, even down to
focal ratio F4. Its 50º AFOV (apparent field of view) was
considered “wide field” for many years, especially when
compared to the Huyghenian or Ramsden designs. It was thus once
purchased as a “premium” eyepiece, often being the most
expensive eyepiece in one’s collection.
Today however, thanks
to modern methods of mass-production and glass coatings, the Plossl
survives today as one of the best optical bargains available to the
amateur astronomer. High quality brands can often be found for under
$50 US Dollars each and even the premium brands like Televue can be
purchased easily for under $100 USD. Practically every brand name
from Astrola to Zhumell has jumped on the Plossl band wagon, and
examples can be found from many countries of origin including China.
Why is the Plossl so
popular today? I’m not sure I know the answer to that. By
today’s standards, it does not have the widest true field of
view, and it is not the design with the sharpest edge of field.
Although long focal lengths have ample eye relief, that shrinks
rapidly when you get below 20mm and below 10mm the design starts to
really get intimate as you squint to view through a tiny top lens
with your eye only a few millimeters from the eyepiece. Today, there
are many brands of 5, 6, or even 8-element designs in the same (or
next) price bracket that for many provide improved viewing
performance. Probably the biggest reason for their popularity might
be the ease and low cost of manufacture while maintaining a high
So just why do I like
Plossls? There are a number of reasons actually. First, Plossls are
light weight. Even the 32mm and 40mm eyepieces weigh in at about ¼
pound. I prefer using altazimuth mounts and I don’t like
fiddling with the balance if I don’t have to. I can run the
gamut of Plossl focal lengths from 32mm to 6mm without rebalancing
the scope on the mount. They are also physically small compared to
their super-wide and ultra-wide relatives, so they take up much less
space in your eyepiece case or bag.
Second, Plossls have
excellent image quality for the money. Can’t afford a Televue
Nagler? The 26mm Type 5 Nagler currently costs $500. For that same
money, give or take a dollar, you can buy every Televue Plossl from
32mm to 8mm, and another $100 gets you the Televue 2x Barlow. For a
$600 investment you are truly good to go for any observing task,
without sacrificing the legendary Televue image quality.
Third, the Plossl line
is usually par-focal, that is, you need little to no refocusing when
you change from one focal length to another. This is helpful when
working at high powers, or with a non-tracking mount.
Fourth, Plossls have
excellent viewing comfort. Well, at least with the longer focal
lengths. 25mm and above are eye glass-friendly, with the 20mm being
marginal. I find that with the shorter focal lengths, I usually get
enough power from the telescope that my astigmatism is negated, so I
don’t need my glasses with them. Still, if you prefer viewing
comfort with short focal lengths, just couple a Plossl with a good
quality multiplier like a Barlow or Powermate. My Meade 5x
TeleXtender turns a 25mm Plossl into a 5mm, and a 20mm into a 4mm,
all with much better viewing comfort, field of view, and eye relief
than comparable focal length Plossls.
Fifth, they come in a
very wide variety of focal lengths, as well as two standard sizes.
The 30mm on up come in the 2” size, and the 40mm on down come
in 1.25” size. And between 40mm and 5mm you can find just about
every number in-between. I have counted no less than 22 separate
focal lengths throughout my collection. Between 20mm and 10mm for
example, I have those two inclusive, 17, 16, 15, 14, 12.4, 12, and
10.5. (I have seen an 18 available somewhere, but don’t have
it… yet.) Now admittedly the difference between 12mm and
12.4mm is about non-existent, but if you are looking for a particular
focal length to fill in your collection, the Plossl design is one of
the first places to look.
Sixth, they make great
eyepieces for use in binoviewers. They have all the qualities I look
for in a binoviewer candidate: light weight, modestly priced,
excellent on-axis image quality, and a clean image usually lacking of
ghosting, glaring, and blackouts. I have four pairs of Plossls for my
Last but not least, is
the variety of “outer wear.” Plossls come in all shapes
and colors, from the “classical” designs out of the Guan
Sheng Optical Company to the more modern Vixen line-up. Some colors
I’ve seen are black, white, gold, and silver; with all kinds of
colors in the trim and lettering. If you’re looking for bling
to enhance your new scope, look for Plossls.
Now you may be asking,
just what turned me into a Plossaholic? It was more by accident than
intent. Many telescope systems come with one or more Plossls. My
first big scope system, a Meade Schmidt-Newtonian, came with a 26mm
4000 series Plossl, and Meade at the time offered the rest of the set
with a case for $99. How could anyone resist! So that was my first
complete eyepiece set of Plossls. When I purchased my Vixen 95L Mak
system, I was so impressed with the design and quality of the 20mm
Plossl that it came with that I eventually purchased the complete
set. This set remains one of my favorites. Plossls regularly come up
on the used markets; and the older, Japanese-made specimens seem to
attract a lot of attention. They are, no doubt, very high quality but
I also sometimes buy “lesser” quality Plossls just to
fill out my collection.
As I mentioned above,
the modern day Plossl design is simply two pairs of elements
separated by an air space. Each identical pair is like the
crown/flint in an achromat refractor’s objective. The two inner
surfaces are convex. Beyond that, I have found some variations in the
design. For example, in the 2002 Meade Catalog, the 3000 series has
flat outer surfaces, whereas the 4000 series has convex outer
surfaces. Others have an asymmetrical design, as in the original
Plossl eyepiece. Sometimes a company may add a fifth element, as in
the Meade 5000 series 5-element “Plossls.” The fifth
element in this case gives the 5000 Plossl a little more eye relief
and 10º more AFOV, but at the expense of a less sharp edge of
field in telescopes with fast focal ratios.
But, enough of my
ramblings; it’s time for the photo tour of my collection!
my very first set of quality eyepieces, the
4000 series Plossls.
Vixen NPL series is another complete
I currently own.
recently, many name brands carried Plossls
the .965” format. Below are two black Celestron
eyepieces with a 1.25” silver top in the center.
made these classic “asymmetrical” Plossls
examples of Orion’s Explorer II set, actually
mix of 3- and 4-element eyepieces. I particularly
the quality of the 17mm for the price point.
eyepieces make great pairs for binoviewers! I
four Taiwanese-made pairs that I regularly use.
4000 series: then (left) and now (right).
Taiwanese-made Astrola’s came with a Hardin
reflector package. I love the gold lettering!
Here are some pictures
submitted for my article by friends and contributors
From Cloudy Nights:
and Sue French own this vintage smooth side Televue
are early versions of the Meade 3000 series owned by
for your enjoyment are Revelation brand Plossls owned
“Great Bear” of CN. The graphics are very nice on this
Sterlings owned by B. Paolini, sold by Smart Astronomy:
gives this set high marks for image quality.
8mm Carton of Japan was submitted by Mike Hosea.
inexpensive eyepiece is currently sold by
Omcon Plossls by Antares are owned by Pollux556,
CN member from Canada.
unusual looking eyepieces made by Sheldon Faworski uses
optics. (A GSO-made specimen is on their left.)
are owned by Joe Doyle.
of course, Plossls come in the massive 2” variety, such as
specimens owned by Bill Paolini (1-1/4” eyepieces shown actual
My thanks to everyone
who submitted their photos for my article!