Mel Bartels' Amateur Telescope Making

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The I.A.U. named asteroid 17823 Bartels discovered 1998 by J.M.Roe in recognition for my contributions to amateur astronomy.




Everyone has the right to see the Milky Way.

Making is the Key to Knowing

Because a telescope mirror focuses light, the mirror's surface must be polished to the astounding accuracy of a small fraction of the wavelength of visible light, a mere millionths of an inch. The feel of the mirror in my hands while I shape it is sublime - time ceases. Designing and building the telescope to hold the mirror involves disciplines from mechanics to software. With such a telescope, the Antennae Galaxies show beautiful tidal streams along with a phantom galaxy near the edge of the eyepiece. To observe objects, I sketch from the eyepiece.

A beautiful telescope brings joy: crisp astonishing images across a range of magnifications. I work on fast and ultra-thin mirrors for 'feet on the ground observing' with lightweight telescope structures. Using design patterns and morphological analysis I unfold the telescope design informed by my observations. I honor masters who have gone before and anticipate those to come.

Seneca said that, "There will come a time when our descendants will be amazed that we did not know things that are so plain to them. . . . Many discoveries are reserved for ages still to come, when memory of us will have been effaced. Our universe is a sorry little affair unless it has in it something for every age to investigate . . . . Nature does not reveal her mysteries once and for all." (Natural Questions Book 7, c. first century)

Russell W. Porter, founder of Stellafane wrote, "For it is true that astronomy, from a popular standpoint, is handicapped by the inability of the average workman to own an expensive astronomical telescope. It is also true that if an amateur starts out to build a telescope just for fun he will find, before his labors are over, that he has become seriously interested in the wonderful mechanism of our universe. And finally there is understandably the stimulus of being able to unlock the mysteries of the heavens by a tool fashioned by one's own hand."

Robert Burnham, Jr. wrote, "The appeal of astronomy is both intellectual and aesthetic; it combines the thrill of exploration and discovery, the fun of sight-seeing, and the sheer pleasure of firsthand acquaintance with incredibly wonderful and beautiful things."

Stephen James O’Meara wrote in his third book in the Deep-Sky Companions series, "As for now, I am living under natural skies. I feel like an explorer who has been given an opportunity to study the last great tract of rainforest. I spend my time documenting everything I see, because I know that there will come a day when everything I see will no longer be regarded as reality but as a myth. I hope that day never comes, but until it does, I’ll be out there seeing what I can see."

My projects - into thin glass

“The difficulty lies not so much in developing new ideas as in escaping from old ones.” — John Maynard Keynes

“Life is trying things to see if they work.” – Ray Bradbury

John Dobson brought us the Dobsonian telescope: big aperture bright views. TeleVue brought us coma correctors and wide angle eyepieces. My vision is developing thin fast meniscus mirror technology so that the Dobsonian 16 inch F5 with its one degree field of view morphs into either a:

  • 30 inch [76cm] F2.7 with the same focal length with a one degree field of view that weighs 100 pounds [45kg] or a
  • 16.25 inch [41cm] F2.9 with the same aperture with a nearly two degree field of view that folds up to fit on a passenger seat in the car and weighs 25 pounds [11kg].

Check out what I can see with high etendue telescopes.

Listen to an interview of me on the Actual Astronomy Podcast, June 2023.

Watch my presentation on software enhancements to my Ronchi Calculator:

Q&A on meniscus mirrors.

Class notes for the 16F3 master meniscus mirror making class.

My 7th thin fast meniscus mirror, 20.25x3/4 inch [514x19mm] F2.9, weighs 23 pounds [10kg], slumped from BVC (Black Vitreous Ceramic), a low expansion laminated glass. This is the final tuneup before working on the 42x5/8 inch [1067x16mm] F2.8 thin meniscus mirrors.

Before the 16.25x3/8 inch [410x10mm] F2.9 meniscus blank became an option, I had ordered a 20 inch meniscus BVC blank. But it failed when I ground through the lamination on the backside. While waiting for the replacement blank, the 16 meniscus blank became available. I completed the mirror quickly and built the mount quickly too (a couple of months total). It is a wonderful scope perfect for outreach and those times when I can't easily haul the 30x5/8 inch [760x16mm] F2.7 telescope. Besides the mirror making tuneup, I wondered if I could make a 20 inch to be like the 16 inch in its portability and quick setup.

I enhanced my Ronchi Calculator with the software nulling feature which I used to make the mirror.

Here is my mirror making log including the retrospective.


2021 Having finished twin 30x5/8 inch [760x16mm] F2.7 mirrors (slumped beautifully by David Davis), I designed and built a lightweight 3-axis telescope that weighs a total of 100 pounds [45kg]. After silvering the mirror under Howard Banich's guidance, I am achieving unprecedented views.
2018 I lept into large thin meniscus mirrors, completing the 25x1/2 inch [635x13mm] F2.6, a slumped mirror blank from Greg Wilhite. I designed a lightweight 3-axis mounting to go with the lightweight mirror with a total weight of 75 pounds [34kg].
2013 I followed with 6 inch F2.8 and 10.5 inch [267x19mm] F2.7 mirrors (another Richard Schwartz slump) to gain more experience. Major success optically and observationally.
Early 2000's looking to make lightweight mirrors, I reasoned that perhaps the difficulty of making stiff cellular mirrors could be replaced by keeping only the face plate and building an appropriate mirror cell behind it. Richard Schwartz, Greg Wilhite and David Davis sent me thin meniscus mirror blanks.
  • Can I make thin meniscus mirrors?
  • If so then how big can I make them?
  • Can I see something new with them?
I began developing an open source software and hardware computerized control system for telescopes in the mid 1980's that incorporated software and hardware innovations. Pat Sweeney designed a PCB in the late 1990's. And in 2000 my wife Barbara and I incorporated BBAstroDesigns, Inc. to sell kits and finished boards. I finished my 20 inch fully computerized telescope in 1994 with which I took some early CCD images.
I began in the 1960's and 1970's by building Palomar 200 inch inspired horseshoe mounted reflectors equipped with homemade cold cameras, processing black and white Tri-X negatives and color Ektachrome slides in my darkroom.

More of my telescopes...

My articles...

John Dobson: the past and the future

Remembering John Dobson
How good were John Dobson's mirrors?
Could the Dobsonian revolution happen again?
Steve Swayze

The largest amateur scopes

Largest amateur scopes (40 inches and larger)

Telescope design

Newtonian reflecting telescope designer...
...what does a telescope do
...how does a telescope work
......scope performance as a function of exit pupil
......focal length and aperture
......focal ratios
......apparent size and image size
......field of view
......four magnifications
......ray tracing
......the eyepiece
......the eye
......diffraction and the Airy disk
......etendue
......high etendue telescopes
......low magnifications
......the ideal telescope
...Richest Field Telescopes
...collimation
...seeing and turbulence
...telescope value
...field curvature
...the nature of telescope design
...folding and sliding scopes
...who invented the reflecting telescope
...helpful formulae
Visual calculator; observing notes
...visual units of measurement
...magnitude scope
...Bortle scale
...object types
...object brightness
...how faint
...aperture vs light pollution
...how to observe
...binoscopes
...night vision devices
Eyepieces
...magnification
Coma corrector
Diagonal designer
...secondary size experiment
...diagonal offset study
...optimize diagonal size
...two unknown optimizations
...off axis mask
Spider and diffraction
Mirror cell
Focuser and baffle designer
Optical layout, baffling
Lowrider layout, baffling
Binoscope
Center of gravity
Tube types
Mount types
...telescope vibration
...ballscopes, take 2
...the Earl of Crawford's tracking arm
...three axis mounts
...the Holcombe mount
...the Morse equatorial to altazimuth transformer mount
Rocker
...friction of movement
Flex rocker
Equatorial table
...omni latitude table
...turret equatorial table
...tilt tracking table
Export and import designs
...30 inch design
...proposed 30 inch binoscope design

Computerized telescopes

Computer operated telescopes

Mirror making

Joy of making mirrors...
...introduction
...rough grinding
...fine grinding
...polishing
...parabolizing
...star testing

Q&A on meniscus mirrors
twin 42 inch F2.8 thin meniscus mirrors
16.25 inch [41cm] F2.9 thin meniscus mirror
twin 30 inch [0.76m] F2.7 thin meniscus mirrors
25 inch [0.64m] F2.6 thin meniscus mirror
large thin mirror grinding
pitch lap calculator
polishing: mechanical and chemical
become a better mirror maker
polish+pitch tips
grinding machine
slumping and precision molds for mirrors
McHardie's 'Preparation of Mirrors...'
16 inch mirror figuring class
mirror making calculators

Mirror testing

Ronchi test
holographic Foucault test
rating mirrors
artificial star testing distance
Waineo null test

Observing

Herschel's Ghosts, observing Integrated Flux Nebulae
Drawings at the eyepiece
Observing dark nebulae
Progressive sketches of supernova remnant G65.3 5.7 north of Albireo
Count the Pleiades
6000X
Preparing for a night's observations
Why observe? Three amateurs speak
An electrophonic meteor; the Leonids
The green flash (and blue flash)
A mountain meditation
Lunar graze occultation
Messier observations
My weather forecasts and dark sky links

Star parties, conferences

Oregon Star Party...
...2023 Oregon Star Party
...2019 Oregon Star Party
...2018 Oregon Star Party
...2017 Oregon Star Party Eclipse Edition
...2016 Oregon Star Party
...2015 Oregon Star Party
...2014 Oregon Star Party
...2013 Oregon Star Party
...2012 Oregon Star Party
...2011 Oregon Star Party
...2010 Oregon Star Party
...2009 Oregon Star Party
...2008 Oregon Star Party
...2007 Oregon Star Party
...2006 Oregon Star Party
...2005 Oregon Star Party
...2004 Oregon Star Party
...2003 Oregon Star Party
...2002 Oregon Star Party
...2001 Oregon Star Party
...1999 Oregon Star Party
...1998 Oregon Star Party

2012 Waimea Hawaii AltAzInitiative
2010 RETA Spain

Imaging old style

Astrophotography
CCD Images

My calculators...

Telescope design

Newtonian telescope designer incorporating a number of calculators
diopters

Mirror making

Ronchi Calculator
artificial star testing distance
holographic Foucault null test, ported to web client JavaScript from Mauritz Andersson's server side PHP
mirror slumping
pitch lap calculator

Visual

magnitude differences
SQM (Sky Quality Meter) readings and unaided-eye magnitudes
object description

Earth and sky

air mass
refraction
precession
astronomical time calculator

Errors

telescope mounting's primary axis errors
coordinate errors (precession et al)

Coordinate converters

sky position to telescope position calculator (text)
altazimuth coordinate calculator including tracking rates (text)
equatorial mount tracking rates calculator, includes refraction (text)
Initialization simulator
altaz telescope 2 star initialization error study using pre-built data
altaz telescope constant motion tracking errors

Motors and encoders

encoder calculator
motor calculator
trajectory

Gauges

gauge study

Unit tests

lib/calcLib unitTests.htm
lib/coordLib unitTests.htm
lib/sharedLib unitTests.htm
lib/motorLib unitTests.htm
lib/encoderLib unitTests.htm
lib/trajLib unitTests.htm
lib/threeAxisLib unitTests.htm
lib/holomaskLib unitTests.htm
lib/objectLib unitTests.htm (takes a few seconds to run)
lib/objectLib data mining.htm (can take time to run)

Earlier webpages

https://web.archive.org/web/*/www.bbastrodesigns.com
https://web.archive.org/web/*/www.zebu.uoregon.edu/~mbartels/
https://web.archive.org/web/*/www.efn.org/~mbartels/

Links

Mel Bartels' homepage

BBAstroDesigns, Inc.

Beginnings

One of my most vivid memories as a child is resting in the back of my parents station wagon while driving back home to the city.
The stars were so bright and the sky so black as I peered out the window.