FX Series Telescopes
The Super FX telescopes
from Starmaster represent a new frontier in
commercially produced telescopes - they are the first large
telescopes offered at a focal ratio F/3.3.
- 20" F/3.3, quartz
primary 1.25" thick (and 4.5" m.a. quartz flat)
- 22" F/3.3, Pyrex
primary 1.5" thick
- 24" F/3.3, Pyrex primary 1.6" thick
coma correctors, cooling, and performance
At F/3.3, visual observing is
uncompromised and made
even more amazing by the Paracorr and awesome Ethos eyepieces from
TeleVue. The new Advanced Paracorr, due out early
promises even better performance with wide field eyepieces like the
20mm Ethos. Objects are as sharp as with slower
instruments, except the observer's feet are much closer to the ground,
or on the ground!
build quality means that these fine instruments stay in
collimation as they move to objects all over the sky, high up and near
the horizon. Carefully designed mirror cells support the optics
properly at all altitudes, and are built solidly to minimize flexure
that could affect collimation. Simply put, once properly
collimated the telescope stays aligned.
Additionally, the fast focal
ratio means that those doing imaging and
observing using high-sensitivity cameras (a.k.a. video astronomy, see John VeDepo's article here) can use shorter
exposure times than slower instruments while their captures a wider
field of view.
This line features another Starmaster first - a telescope with all
quartz optics. Inspired by Mike Lockwood's 1.25"-thick 20" F/3
mirror, the 20" F/3.3 features a 1.25"-thick quartz
mirror, the same thickness as the 14.5" and 16.5" FX telescopes' Pyrex
primary mirrors. These three models currently are the fastest
and lightest weight primary mirrors (of comparible size) in the
commercial Dob market.
the Super FX line provides the same performance as other
telescopes, but in a much shorter package.
As Mike Lockwood says, "Given good optics and seeing, the main
factors limiting performance in a telescope are thermal
equilibration and proper collimation."
addressed these factors and minimized their effect to ensure
maximum performance and maximum quality observing time.
You can read
about Mike's 20" F/3 MX, the telescope that proved that F/3.3 visual
telescopes were doable, in three articles linked from the Online Articles page.
ladder or chair (if any) do I need?
The 20" F/3.3 allows seated observing all
over the sky. Rick and
Mike both enjoy seated observing because it is more comfortable, less
fatiguing, and it allows the observer to see more detail in both
deep-sky and planetary views.
The only disadvantage to seated observing is trying to
get your friends out of your observing seat so you can observe!
If you're about 6' tall, the 22" F/3.3 requires one step to view at the
zenith, and seated observing is possible over most of the rest of the
sky. (See image at the top of this page.) The 24" F/3.3 needs one more step.
Weights, dimensions, eyepiece heights, etc. are provided on the Telescope Specs page. For other
questions, give Rick a call.
Here's a link to an article
about the Fall 2009 Chiefland Star Party.
A brief report by Rick is followed by comments from two
Starmaster owners who report on a 30" F/3.3 and other Starmaster
telescopes. Also see Rick and Mike's report about the 2009 Okie-Tex Star Party and the 22" F/3.3
Super FX that Rick brought.
the 20" and 22" F/3.3 Super FX telescopes
A number of people have asked,
besides price, what's the difference between the 20"
and 22" F/3.3 Super FX? This is a great question, because there
are some noteworthy differences depending on what is most important to
the future owner.
The advantages of the 20"x1.25" quartz blank over the 22"x1.5"
Pyrex blank are 1) lighter weight, 2) faster cooling time, and 3)
on the mirror figure while cooling.
The 20" will have a 1.25"-thick mirror, so it will cool faster than the
1.5"-thick 22" F/3.3. (Currently a 20" diameter piece of quartz is the
piece I can get for prices that are reasonable and appropriate for
The quartz blank is thinner, weighing ~27 lbs. for the 20"x1.25" blank,
the 22"x1.5" weighs 41 lbs. This is a 14 lb weight savings, important
with back problems.
Quartz has a coefficient of thermal expansion (CTE) that is about 1/6
Pyrex. This means that the mirror, with one curved surface and one flat
surface, will distort less during cooling due to the internal thermal
This gradient usually causes mirrors to appear overcorrected while
cooling. (Mike notes this effect on his thin Pyrex 20" F/3 was
definitely moving this direction
cools off a short time later.)
Thinner mirrors seem to change correction more, but they cool faster,
effect goes away sooner. Quartz allows one to utilize a thinner mirror
greatly reduce the effect of this cooling-induced correction change.
So, under serious cooling, the 20" quartz mirror will likely show less
correction error than the 22", and it will definitely cool off faster.
provides more quality observing time. Once the 20" and 22" are roughly
equilibrated, the 22" will have the advantage due to larger aperture.
Just for perspective, keep in mind that we're comparing two thin
both will cool off much more quickly than 2"-thick optics.
Finally, in terms of physical size, the 20" scope will be shorter and
compact in size than the 22", and that may be important for those with
vehicles or narrower doorways to pass through between scope storage and
All major components of
Starmaster Telescopes are made with pride in the United States of
America by small, community based companies.
-Cancelled orders will be subject to a restocking fee which will be
to 15% of the BASE price of the telescope, NO EXCEPTIONS.
-Orders are not transferable without permission of Starmaster
Telescopes and will be subject to additional fees.
-We are now accepting international orders for telescopes 22" in
aperture and under.
comments or questions about this site, email Starmaster Portable Telescopes.
has a second passion besides astronomy - Click
here to see what it is!