Tips to Improve Telescope Performance
Comments after 50 years of observing and telescope making, by Mel Bartels
My list is quite different from the usual run of the mill lists because
I have found that improving myself, not obsessing over the telescope,
the key to deeply satisfying sessions at the eyepiece.
I have found three factors, in order of importance:
- The observer
- The skies
- The telescope
I've seen too many cases where an experienced observer sees more from urban skies than a beginner from dark skies.
I've seen too many cases where the telescope is blamed when the problem lay with the observer or the skies.
Let’s dispense with the myth that aperture makes all the difference.
One of the greatest observers of all time, Stephen O’Meara, uses a 5
inch [13cm] telescope. I’ve seen expert observers work their magic with
telescopes regardless of the telescope’s aperture and quality. I’ve
never seen an increase of aperture turn a so-so observer into a great
observer. I have witnessed amateurs regrettably leave the hobby after
quickly jumping up in aperture or purchasing expensive high-end
telescopes, their dreams unfulfilled. A common progression goes like
this: entry level middle of the road scope, then a larger aperture
scope followed ultimately by the realization that aperture does not
make the observer followed by stirring a smaller scope into the mix.
Advanced amateurs favor telescopes optimized for their favorite
objects: giant telescopes for clusters of galaxies, long focal ratio
scopes for lunar and planetary, very portable scopes for traveling to
To an experienced observer, transparency is everything. A wonderfully
transparent night renders aperture insignificant. Every telescope
becomes a winner on an exceptional night. Use weather forecasts along
with Clear Sky Clock to target those transparent nights. Learn to look
for signs of excellent transparency during the daytime such as blue sky
right up to the edge of the Sun (mask the Sun with your hand), jet
trails (the trails should be short, not stretching across the sky,
indicating a dry upper atmosphere), and clear sunsets and sunrises.
Here are my top tips.
What about the endless myopic discussions on internet forums? I offer
one word of advice: pay attention to experienced telescope makers who
are also experienced observers. Two joys await the amateur astronomer:
making a telescope then using it to view the heavens. Each telescope
made is a departure from the previous telescope as the maker applies
hard won lessons to satisfy desires. Lessons learned at the eyepiece by
the telescope maker are lessons of hard truth. Search out these people
as they are often busy observing and building.
- Remove the lens cap.
Seriously. It's happened to the best of us, leaving a stop-down
off-axis mask in place all night, wondering why the views are dim,
wondering why that object cannot be found.
- Overcome your cognitive biases.
Most amateur beliefs about telescopes and observing result from bias,
are simply not true, and seriously limit your observational results.
- Observe, observe, observe. There is no substitute for hours at
the eyepiece. How often do you observe a week? What can you do to
increase your observing hours? Make the telescope more portable, join
others observing. Aim to observe one to two times a week on
average. Malcolm Gladwell’s book, “Outliers”, states that
thousands of hours of practice are necessary to become an expert. How
many hours do you think that Stephen O’Meara has observed? How many
- Keep an observing notebook. Sketch, sketch, sketch. It’s
not about the drawing as much as it is about your skills to notice
detail. Study the objects ahead of time. Locate them on a planetarium
sky chart and note how best to star hop to them.
- Dark adapt your eyes and work to keep them dark adapted. Use an
eyepiece shroud. A variable brightness dim light flashlight makes a big
difference. And set your planetarium programs on tablets to night mode
along with red or green covers that further dim the light.
- Learn how to use your eyepieces.
Ever watch attendees at public star parties use your scope for the
first time? They move their eye around searching for the field, in and out, left and right, up and down. You too
need to learn how to position your eye and how to observe the field of
view for each eyepiece. If you must use glasses then be sure to pick
eyepieces with sufficient eye relief.
- Take time at the eyepiece for each object. More time spent observing an object is like increasing the aperture and resolution of your telescope!
A few minutes brings
awareness to detail that’s thrilling and satisfying but do not stop
there. More awareness and detail comes after observing for an hour or
more on an object. The most difficult objects are only there 20% to 50%
of the time. The seeing will stabilize and your concentration will be
at your peak with your eyes paying attention to the proper place in the
field for a few moments. My personal standard is that I have to see the
object or detail in question three times over a 20 minute session to
say that I ‘saw it’. Observe for yourself. The vast majority of
observers are truthful to themselves, knowing or not caring that they
will fail to convince doubters. It’s all subjective. Look at sketches
by observers. Each observer tends to notice or emphasize certain
features. They can invariably be traced back to digital images, to
reality. I study digital images ahead of time, to get a sense of detail
that might be glimpsed. If I see it, great; if I don’t, that’s great
too. Knowing that it is beyond my observational powers is worthwhile
too. I certainly add the negative results to my lists of “impossibles”
to go after on those rare nights of perfect transparency when I find
myself under the darkest skies.
- Get a dark sky or nebula filter. These filters really help to
make subtle detail more noticeable. A filter is more important than
aperture because a nebula filter increases contrast more so than
can you do to increase comfort at the eyepiece? A better
observing chair, rotating the focuser to a better viewing angle, a
small table next to you for your eyepiece case, tool chest and tablet,
eyepiece cases that make it easy to retrieve and swap eyepieces. Use a
checklist for your gear. I have a couple of checklists, one for short
trips and one for longer multi-night star parties.
different eyepieces, try different filters. Walk away for a
minute then return to the eyepiece. Aim the scope at different points
in the field of view. Test your exit pupil by using your lowest power
eyepieces. Calculate the exit pupil of the telescope-eyepiece by
dividing the eyepiece's focal length in mm by the scope's focal ratio,
e.g., a 20mm eyepiece used with a F5 telescope gives an exit pupil of
20/5 = 4mm. Defocus slightly to see if you can see the primary mirror's
edge (hint: look for the edge clips). If so then your eye covers that
exit pupil. Borrow lower power eyepieces from friends until you find
your eye's limit. You may be surprised by how big of exit pupil you can
- Consider the interplay between aperture, magnification, apparent field of view and exit pupil.
Aperture sets star brightness and magnification along with field size
given a standard set of eyepieces. Magnification sets the image scale.
Apparent field of view sets the overall width of the field. Some like
wide fields, others like narrow fields. Eyepieces designed for wide
fields perform slightly differently than narrow field eyepieces.
Finally, exit pupil sets background brightness.
- Drink water during the night, rest your eyes periodically, don’t
strain your eyes during the daytime with bright light - instead use
good sunglasses, have snacks on hand to fight off tiredness and dress
warmly in layers.
observing oriented star parties like the Oregon Star Party. Talk to the
top observers (like Chuck and Judy Dethloff and Howard Banich) and read
their writings. Usually in
their introductory comments and occasionally while talking about their
observations, they will mention what they do to improve their
observations. Read their comments a second time and then a third time.
- Find dark skies. Enough said.
is the single greatest improvement that you make to your telescope.
Improve the telescope’s baffling until you cannot detect any
glare through your eyepieces from a flashlight aimed at various angles
at the telescope by a friend. Most important are the focuser baffle,
the diagonal baffle and the primary mirror baffle. For more see my diagonal baffle calculator.
- Optical alignment or collimation. Keep it simple:
precisely center dot your primary with a notebook ring, use a good
laser collimator to adjust the secondary until the laser points exactly
in the center of the primary (rotate the laser to confirm that there is
no wobble or angle to the laser), finally adjusting the primary so that
the return beam coincides with the start of the laser beam. For more
see my page on optically aligning a F3.0 telescope.
- Add tracking to your
telescope if the field of view is under a degree. Motorize the
equatorial mount, computerize and motorize the altazimuth mount, or
place your telescope on an equatorial platform.
- Cooling the primary mirror to the night time ambient temperature. A 0.1 degree difference within the primary mirror amounts to a tenth wave error.
- A precision focuser with a two stage knob, particularly if the
focal ratio is very short. The zone of good focus on a F3.0 mirror is a
thousandth of an inch.
- Advanced observers should consider a second telescope specialized for their interests.
What about exquisite optical quality and high end equipment? It’s
natural to want the best; we all strive for it, but will it magically endow you with hundreds
of hours of observing time? At star parties I tend to gravitate to the
humble observer with the used looking telescope, maybe a bit scuffed up
from many nights of use, with optics of decent quality.
For example, thanks to the Demonination Bias, amateurs will pay much
more money for a 1/12 wave mirror than a 1/8 wave mirror, yet the
difference between these two ratings is far smaller (three times
smaller) than the difference between 1/4 wave and 1/8 wave, a
difference in some cases that is worthwhile.
The beauty of the Universe, stunning and sublime at once, draws us all.
May you find yourself under stars observing the next clear night!
--- Amateur Astronomer's Handbook by J. B. Sidgwick
--- Deep Sky Companions: Hidden Treasures by Stephen O'Meara
--- Nebulae and how to Observe Them by Steven R. Coe
--- The Night Sky Observer's Guide Volume 1, by George Robert Kepple nad Glen W. Sanner
--- Observing Handbook and Catalog of Deep-Sky Objects by Christian B. Luginbuhl and Brian A. Skill
--- Philip's Obesrver's Handbook Astronomy from Towns and Suburbs by Robin Scagell
--- Visual Astronomy of the Deep Sky by Rober N. Clark
--- Webb Society Deep-Sky Observer's Handbook, Volume 5 Cluster of Galaxies, by the Webb Society Kenneth Glyn Jones, editor
--- my web article on Visual Astronomy
--- my web article on observing dark nebulae