Mel Bartels' Amateur Telescope Making

My telescopes...

My articles...

What's New

I'm busy updating my meniscus mirror thinking; adding to my star testing article a comment about the optimum star testing elevation, a realization that when a zone's location becomes difficult to locate using the star test, it's a sign that the mirror is diffraction limited; adding to my polishing a mirror article how to fix astigmatism with a local lap; and links to Kai Kretzschmar's 47 inch project: slumping and grinding, on my precision mold making for slumping mirrors webpage.

Drawing of the river of dark nebulae that leads north of the North American Nebula.

Drawing of M15 with surprising nebulosity nearby. What is the nebula - emission, Milky Way or ?

What an amateur astronomer needs to know about the Airy disk.

Understanding telescope magnification is the key to using a telescope.

The Bartels' equation for telescope value.

Another astronomical truth: when aperture differences matter.

Some thoughts on telescope requirements.

Preparing for a night's observations.

Why observe? Three amateurs speak.

My latest drawings. First, the Cave Nebula or Caldwell 9. Next, a dynamic complex of dark nebulae, stars and Milky Way next to Albireo. A cure for Albireo Myopia?

The Oregon Star Party Telescope Walkabout for 2015 featured eight telescopes: Don Peckham's new Tenesegrity telescopes, Rob Brown's white light sun bucket solar scope, Hitoshi Yokoyama's binocular telescope from Japan, Frank Szczepanski's unequal large aperture binocular, Bill Fates beautiful 5 inch binoculars, Scott Lee's 14 inch novel Newtonian, Greg Rohde's well-built computerized digital drive system and Jerry Oltion's equatorial table adaptation.

Some thoughts on how to become a better mirror maker.

I dug out my old notes on my secondary size study from the 1970's using my wonderful 14 inch telescope.

Progressive sketches of supernova remnant G65.3 5.7 north of Albireo.

I'm adding Howard Royster's 1 meter alt-alt to my largest amateur telescopes page.

I've ported Mauritz Andersson's ground-breaking mirror test ( to JavaScript so that it runs entirely in the browser. Mauritz's made the source code open source under the MIT License (

The toolmaker, the thinker and the telescope. More astronomical truths...

Richest Galaxy Observing. With my 10.5 inch [27cm] f2.7 scope with 2.5 degree field I'm able to see the Leo Triplet plus a fourth galaxy further away; I'm able to capture the Markarian Chain from M86 and M84 sweeping across to M88 and down to M87. Also I glimpsed a rarely seen dark nebula to the south. Field after field is littered with galaxies; often 5-20 galaxies in any field of view as I sweep through the Virgo / Coma Berenices region. I call this "Richest Galaxy Observing".

Amateur astronomy truths...

What is TTO and TEO?

Is aperture king? Let's compare the Sombrero Galaxy through side by side 6 inch and 13 inch telescopes across a range of magnifications.

I wrote a new calculator that shows altazimuth tracking errors when the motors are commanded to move at a constant rate. It illustrates how long altazimuth constant rate tracking can continue before the error becomes too great.

I built a new aperture calculator that determines aperture from exit pupil, the eyepiece field stop diameter and the desired field of view.

I've put my thoughts on star testing into its own webpage.

See my thoughts on the Earl of Crawford's tracking arm.

New sketches of the Horsehead area and the Pleiades.

Check out my awesome observations of the Orion-Eridanus Super Bubble, SH2-245, SH2-264 and the southern arc of Barnard's Loop.

See my sketch of Comet Lovejoy with my 13 inch [34cm] F3 telescope.

I extend the Morse transformer design to three axes and to a side mount.

I investigate the tilt tracking table and hexapod mount with a fellow tilter. Can they replace the equatorial table?

Can an equatorial table be designed to use simple Dobsonian motions? Continue reading about my turret table design...

I've added a provocative section to my re-designed Richest Field Telescope article. In it I make the case for "telescope mode" observing. Continue reading my RFT article...

My links for weather forecasts and dark skies. Check out my links...

50 inch F3.5 amateur telescope, mirror by Fullum, appears in California. I've added it to my list of world's largest amateur telescopes.

Dynamic collimation, the Andrew Angle and the Seven Ways. Recently I was sitting on Jerry Oltion's couch, mulling over his collimating approach to his spectacular 12 inch binoscope. You really need to know your way around collimation if you own a binoscope. It occurred to me that there are seven ways to collimate a reflector. At the same time Andrew Bell was finding collimation issues with his telescope: the collimation would change as he tipped the scope up and down. What is the best angle to aim the scope to minimize collimation changes? Andrew devised a mathematical approach to calculating the optimum angle. Get the lowdown...

I am observing features in my small super fast reflectors like the Pleiades Bubble and the Andromeda Shelf that apparently have not been observed; at least there are no records that I can find. Why? Read my thoughts...

Seeing the unobservable: wide angle nebulae in my small Richest Field Telescopes. See my sketches...

My latest telescope, a 10.5 inch f2.7. It resolves globular clusters yet provides a two and a half degree field view. Just spectacular and a joyful scope to operate. See my scope...

The small scope, a 6 inch f2.8, that stunned me on the very first object I observed, the Pleiades, revealing a bubble surrounding the cluster that can only be seen on deep digital images. This scope cries out to be looked through. See my scope...

Improved folded Newtonian calculator: the tertiary mirror can be moved. Play with the calculator...

I follow an explicit plan for telescope innovation. Using this plan I've designed innovative scopes such as the ZipDob, the TriDob, super fast meniscus Scope.exe and computerized telescopes. Read how I innovate...

I am now making slumping molds up to 42 inches in diameter to curve large glass into a meniscus shape that survive through multiple kiln cycles. See the molds...

A review of the rare George McHardie's "Preparation of Mirrors for Astronomical Telescopes". A wonderful little instructional pamphlet that emphasizes the practical. Turns out little has changed, plus some forgotten tips. Read my review...

The 2014 Oregon Star Party Telescope Walkabout. Three bino-scopes, two scopes faster than F3, plus a lot more. See the scopes...

The night of 6000x power; when we ran out of doubly stacked barlows. Read about that astonishing night...

An electrophonic meteor and the Leonids..

I've made observing dark nebulae my specialty the past several years. Some thoughts on dark nebulae, observing them, and lots and lots of sketches. Read how I observe and see my sketches...

The 2012 Waimea Hawaii AltAzInitiative conference and a trip to Mauna Kea. See pictures of the giant telescopes...

A mountain meditation. Observing in the rugged Oregon Cascades one summer evening. Continue reading...

Mel Bartels' homepage

BBAstroDesigns, Inc.


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.

My telescopes...

My articles...


Who invented the reflecting telescope?

Remembering John Dobson

The Morse transformer mount

The Holcombe mount

The future

Can the Dobsonian revolution happen again?

Telescope makers' future

Amateur astronomy's future


Rich Field Scopes

Folding and sliding telescopes

Diagonal sizing

Variations on the ballscope

Flex rockers

Secondary size study

A smaller upper cage

Off-Axis masks

The Earl of Crawford's tracking arm

Omni latitude equatorial table

A turret equatorial table

The tilt tracking table

Three axis mounts

Ultra-Light Dobsonians

Telescope vibration

Telescope innovation

Natural telescope design

A new way to look at things

Some thoughts on telescope requirements

Largest amateur scopes

Largest amateur scopes (40+")


Amateur astronomy truths

Bartels' equation for telescope value

Tips to improve your telescope

Dynamic collimation

Collimating a f/3.0 telescope

Telescope slang

Mirror making

Joy of making mirrors...


rough grinding

fine grinding



star testing

Become a better mirror maker

Precision molds for mirrors

Sagitta calculator

Mirror slumping calculator

Ronchi test

Artificial star testing distance

Large thin mirror grinding

Rating mirrors

Polishing theory

Polish+pitch tips

Ronchi mirror test

Waineo null test

McHardie's "Preparation of Mirrors..."

16 inch mirror figuring class

Some calculators

Newtonian baffling

Movement friction

Folded Newtonian

All calculators...

Computerized telescopes

Computer operated telescopes

History of computerized telescopes

Telescope mounting's primary axis errors

Coordinate errors


Coordinate calculator + tracking

Equatorial tracking rates calculator

Astronomical time calculator

Sky to telescope position calculator

Motor calculator

Trajectory calculator

Initialization simulator

2 star initialization study