Our Richest Field Telescope

Fifty Years 1975 – 2025

This is a Richest Field Telescope (RFT). Its large achromatic objective lens (5”) and short focal length (24-3/4”) makes it ideal as a “comet hunter.” It has a wide-field of view (4°), low-power magnification (16.5x) and excellent light-gathering ability (f/5). It was constructed as a father-son project by my father John E. “Jack” Voisin (1925-1994) and me, John M. “Mike” Voisin.

(A PDF version of this essay is available here. Enter user name “Guest” and password “seemore” when prompted.)

I taped a quarter in a letter to A. Jaegers Optics company to request the plans for this telescope on 4 February 1975. We ordered the parts 26 March 1975 and after they arrived we began work 17 April 1975. Busy most evenings after my father’s normal job, we finished 23 May 1975. The tripod and equatorial mount with custom enhancements took another month to complete.

The telescope was a pre-designed “kit,” but rather than being self-contained, the various parts had to be ordered individually. It was available from, and marketed for several years by, A. Jaegers Optics company, mainly through their catalog and full-page advertisements in Sky and Telescope and other astronomy magazines. They sold the lens, lens cell, tube, a reprint of the instructions, a super-sized eyepiece mount, and a war-surplus, wide angle “super” Erfle eyepiece. We also bought a couple 1-1/4” eyepieces and an adapter to fit the odd 2-19/32” inside-diameter eyepiece mount.

We purchased other items from Edmund Scientific company to complete the telescope. These included the finder scope, finder scope mounts, heavy-duty wooden tripod, German equatorial mount, and electric clock drive.

My father made a custom saddle to attach the telescope to the equatorial mount. He made it from a section of pipe slightly larger in diameter than the telescope tube.

He had access to a machine shop at the pipeline company where he worked. In those days, it was a two-story tall building. Up towards the rafters was a spinning shaft with several large wheels attached. It ran overhead for the length of the building. To use a particular metal saw, drill or lathe, he would throw a lever to engage the machine’s belt to the corresponding wheel spinning overhead. A single large and loud engine powered the drive shaft and consequently any machines having their belts engaged.

My father fabricated a metal disk or plate to enhance the stability inside the tube, adjacent to the eyepiece mount. The original design had such a plate, but Jaegers thought it unnecessary for the super eyepiece mount. We strengthen it because we planned to attach a camera.

Each Edmund Scientific counterweight had a hole bored in the side, but no provision for a set screw to attach a rod and radial counterweight. So my father customized it by threading the existing hole. He then used a lathe to shorten and turn a large bolt to make a small adapter to accept a steel rod. He turned another small counterweight out of solid brass. Once the adapter/rod was screwed into the original counterweight, the smaller counterweight could slide back and forth along the same axis as the telescope tube. Thus we could change out an eyepiece with a heavier camera by simply adjusting the small radial counterweight.

He also used a lathe to turn magnesium-alloy tubing to make adapters for the super eyepiece mount. One was to accept 0.965” eyepieces that came with our existing 2.4” Sears refractor. Another was to attach a single lens reflex (SLR) camera body directly to the eyepiece mount, using the “direct objective” method. Another was to attach an SLR camera using the “negative projection” method. With it, a regular camera tele-converter lens fit inside the adapter, which was then inserted into the barrel of the eyepiece mount.

Although the objective lens was touted as “unsurpassed” and “exceptional,” a former part-time employee, Stephen L. Nightingale, writes online that testing was not rigorous. Our lens unfortunately suffers from comatic aberration, where stars appear to flare out towards the edges of the field. But still, it is a delight to behold the starry sky with this fine instrument. It survives in nearly pristine condition fifty years later. Only the rubber gaskets near the right ascension and declination dials have rotted away and the light-absorbing foam we sprayed black and used to lined the inside of the tube is deteriorating.

Then as today, mail-order shopping was a challenge. In early May 1975 we received the equatorial mount. Unbeknownst to us the price had increased and Edmund Scientific invoiced us an extra $36.55. We probably ordered from an outdated catalog. Quality control was not the best. Some of the small hardware was missing, the plastic pointer on the declination circle was broken off, and the counter-weight set screw was bent during shipment. The finder scope ring mounts were very roughly cast and required filing and re-tapping the set screws.

We ordered two 1-1/4” Orthoscopic eyepieces from A. Jaegers. When we received them, they had substituted a different focal length for one because it was out of stock. The other had an air bubble in the center of the lens and we had to send it back for replacement.

All told, parts and accessories for this telescope cost $533.80 in 1975, not including incidental hardware and supplies. That’s relatively expensive in 2025 dollars at $3,237. Being a kid I didn’t realize just how expensive it was, until now.

A Fifty Year Legacy

My father trained as a “bombagator” during World War II, which was a combination bombardier and navigator in preparation for B-29 bomber flights over Japan. His interest in astronomy was reinforced by his training as a navigator. He frequently sat in a lounge chair on the back patio with a pair of high-power binoculars scanning the stars. He taught me to “navigate” the sky also, pointing out the constellations, every bright star by name, and the galaxies and nebulae.

He instilled in me a great sense of wonder about the universe and he actively encouraged my own interest in astronomy. In the summer of 1973 he bought a small reflector telescope, probably a 3” from Sears or Edmund Scientific. Although exciting, it was difficult to track an object with its altazimuth mount. It was also frustrating to keep collimated. He soon returned it and bought instead a 2.4” refractor from Sears, which I still use today.

During our family summer vacations, we often stopped at places connected with astronomy, like the National Radio Astronomy Observatory,¹ the Kennedy Space Center,² the National Bureau of Standards,³ and the atomic time-signal radio station WWV.⁴ We frequently visited the Abrams Planetarium⁵ during Sunday day-trips to visit relatives. After long hours at his job, he still found time to drive me to monthly meetings of the Sunset Astronomical Society,⁶ a round trip of sixty miles. He wholeheartedly supported me when I was elected club secretary at age 16.

We both, but mainly my father, worked countless hours constructing this 5” RFT, and designing and fabricating parts and accessories. I cherish the time I spent with him, the knowledge and skills he taught me, and the many philosophical conversations we had.

Our last adventure together was a trip to Hawaii to view the total solar eclipse of 1991 and to tour the Mauna Kea observatories. After considerable planning, and preparing all our cameras, lenses, filters, test exposures and tripods for the trip, the clear sky clouded over at the last possible second and we didn’t see totality.

Today when an astronomical event occurs, like a comet, a conjunction, or a lunar or solar eclipse, I recall my father’s enthusiasm and all our planning and discussions. I still set up our equipment, much of it handcrafted by him, and observe the heavens just as he would, just as we did.

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Above is the first page of the instructions I purchased from Jaegers for 25 cents. They were a reprint of an article in Amateur Astronomy Handbook ⁷ magazine published in 1960. It was basically an advertisement for Jaegers’ parts. I serendipitously found a copy at a used-book sale several years ago and I was very surprised to turn the page and see it.

Jaegers revised the design to employ their wide-angle Erfle eyepiece and super eyepiece mount.

The illustrations that follow are from the A. Jaegers catalog.⁸

The following are excerpts from the Edmund Scientific catalog.⁹

This illustration is from the instruction manual for the Edmund Scientific clock drive.

Here are two examples of the copious sketches, notes and calculations my father made to design and machine the adapters used to attach a camera to the telescope.

Here is the “negative projection” adapter that resulted from the sketches above, a little worn from use. A Pentax H3 single lens reflex (SLR) camera with a lens extension tube screws onto the 49mm threads protruding from the front of the adapter. Those threads are actually the camera’s regular tele-extender lens. It simply slips into the adapter from the under side. Everything is held in place by thread tension. The adapter with attached camera is then inserted into the telescope’s 2-19/32” super eyepiece mount.

My father turned the adapter below so we could use 0.965” eyepieces from our Sears 2.4” refractor. Notice the set screw is actually a small bolt with a couple nuts that have been rounded over and then knurled with a file. The face of the adapter is a fan shaft friction disk from a John Deere tractor.¹⁰

The next adapter used the “direct objective” method of astrophotography, but it may have been experimental. I don’t recall using it. It employed a combination of old camera filter threads and/or extension tubes to mount the camera body directly to the telescope.

Alternately we could attach this adapter to the front of a regular camera lens just like attaching a camera filter. This used the “afocal” method, but without the telescope eyepiece. The camera lens could also be used in reverse by using a different combination of extension tubes and step-up adapters.

Note the detail in turning these magnesium-alloy tubes. The openings were just wide enough to allow threads to protrude. The metal was thin, but thick enough to hold the device tightly when threaded together. The adapter is slightly smaller in diameter at the back, allowing it to be inserted into the eyepiece mount without binding. The band at the front is thicker, and just smaller than the eyepiece mount opening. It also has a single groove, into which the set screw protrudes when tightened, insuring it will not slip out of the eyepiece mount.

Here is the custom radial counterweight assembly, showing the small bushing turned from a large bolt. It screws into the original counterweight. A steel rod is held in place by a set screw. The brass weight was turned to be just heavy enough to counterbalance any equipment we might attach to the telescope.

Here is the war-surplus wide-angle Erfle eyepiece sold by Jaegers, along with the bushing they sold to use regular 1-1/4” eyepieces with the “super” eyepiece mount.

The photo below from 1975 shows the newly-made accessories. On the left, the camera is attached with an extension tube to the “negative projection” adapter. On the right, a camera lens is attached to the “direct objective” or “afocal” adapter. Bottom right is the 0.965” eyepiece adapter.

Top center is a partially-completed variable-frequency control my father was building to slow down or speed up the electric clock drive for use during astrophotography. He used plans described in the August 1975 issue of Sky and Telescope magazine.¹¹ He went on to other projects though and never finished it.

Here’s the 5” RFT set up in the backyard, 1977.

Here it’s set up to observe the partial solar eclipse of 1979 during my high school physics class. A number 16 welder’s filter covers the objective for safe viewing.

And fifty years later, the 5” RFT is still a tribute to my father’s craftsmanship.

1. Green Bank, West Virginia.
2. Cape Canaveral, Florida
3. Boulder, Colorado.
4. Fort Collins, Colorado.
5. Michigan State University, East Lansing, Michigan.
6. Midland, Michigan.
7. Lloyd Mallan, Amateur Astronomy Handbook, Fawcett How-To Book #454, 1960.
8. A. Jaegers Optics, Catalog 1975-6.
9. Edmund Scientific Co., Catalog 661, circa 1975.
10. The face of the adapter has a marking, D396R, stamped on it. Thinking it was a random piece of scrap metal, I searched the Internet anyway and found it was actually a common John Deere tractor part.
11. John B. West and Robert S. Bradford, Jr., A Crystal-Controlled Oscillator for Telescope Drives, in Sky and Telescope magazine, August 1975, pages 125-127.