§ 3.1. Design Changes and Refinements

Evolving Specifications

42.4 Inches at f/12.1

The company specified its first production Questars as “catadioptric apochromatic photo-visual” telescopes with an effective focal length of 42.4 inches (1077mm) and a focal ratio of f/12.1.

These precise specifications first appeared in the company’s advertisement in the February 1957 issue of Sky and Telescope. They appeared again in that magazine’s November 1958 issue and in the October 1958 Questar booklet with addenda dated June 1959.^[4]

On production units, these specifications persisted into July 1960 if not later.^[5]

45.5 Inches at f/13

Months before, however, Questar had begun to indicate a “variable focal length” of 45.5 inches (1156mm) and a focal ratio of f/13. Presumably in an effort to indicate camera bodies coupled closely with the telescope and coupled with extension tubes, the company added two specifications for photographic focal length and ratio: 49 inches at f/14 and 56 inches at f/16.

The company had decided upon the change by the time it printed its 1958 Questar booklet with prices and addenda dated September 1959, only three months after the prior edition.^[6]

But the company must have spent the remainder of 1959 and at least the first four months of 1960 working through its existing stock of moon map telescope barrel skins that indicated Questar’s focal length and ratio as being 42.4 inches at f/12.1. When it exhausted that stock, the company began indicating the new specification on telescopes that it shipped to clients.

Production units specified with a focal length and ratio of 45.5 inches at f/13 appeared only briefly between early or mid-1960 and the spring of 1963.^[7] For some specialty units such as those with quartz mirrors, Questar may have used remnants from its older stock of moon map skins that were marked with a visual focal length of 45.5 inches at f/13 as late as 1965.^[8]

50.5 Inches at f/14.4

Questar then listed a third and final specification for an effective visual focal length and ratio of 50.5 inches (1283mm) at f/14.4. The company explicitly indicated that “close coupled cameras” operated at 56 inches at f/16 and that cameras “with reflex housings” or extension tubes did so at 64 inches at f/18.

While the possibility exists that owners of units built prior to 1964 may have had the moon map skin replaced with new specifications when they sent their telescope in for service, Questar likely began indicating this focal length and ratio of 50.5 inches at f/14.4 on new units as early as 1963.

In its promotional literature, the company first indicated the change in its July 1964 Questar booklet.^[9] All subsequent marketing printings showed these updated figures.

Longtime Questar manager Jim Perkins notes that, as of 2020, 3.5-inch systems have a computer-modeled focal length of 1269.7mm (50.0 inches) and an effective focal ratio of f/14.2. Slight variations may exist due to machining tolerances and optical curve variation.^[10]

Reasons for the Changes

During its first decade of production, Questar twice changed its specification for focal length and focal ratio. On both occasions, there was a period of time during which the values the company indicated on its production units and in its advertising and promotional literature were out of sync. The company probably engaged in cost savings by using up its existing stock of moon map tube skins with older optical specifications etched onto them before switching to new stock with updated specifications.

But why did Questar make these changes to begin with? Why did the company implement three different focal lengths over its first ten years of production? What optical performance benefit or manufacturing efficiencies did Questar gain by making the change?

Contrary to what these varying focal length markings may lead one to believe, the real reason for the change may simply have been the result of measurement errors. As longtime Questar associate Rodger Gordon pointed out, the Standard Questar’s optics have always been figured with an effective focal length of 50.5 inches at f/14.4. The other figures were simply the result of a miscalculation.^[11] Jim Perkins has also raised the possibility that the earliest primary mirror and corrector lens sets that Questar used during its days of doing business with Cave Optical Company may have had variations in focal length. This may have been due to the fact that optic sets, whose components came from different vendors, were unmatched. But after Questar began work with J.R. Cumberland, production became far more uniform and reliable. Perkins further stressed that optical calculations, which are difficult to make under any circumstances, were manually performed by “paper and slide rules” during the company’s early years.^[12] It would have been only natural for one to encounter variability in focal length measurements during this period.

The existence of pre-1963 Questar telescopes that show evidence of later modification and that have up-to-date focal length and ratio markings of 50.5 inches at f/14.4 indicated on their barrels is further evidence that Questar often updated instruments to current standards when their owners sent them in for service. One clear example of this is Questar #0-829. Built in November 1960, the company performed updates that brought it closer to modern standards in January 1965. Part of the work that Questar performed on that instrument included the replacement of the barrel’s moon map skin with one that indicated the latest focal length and ratio standards.^[13] Since it is always possible that older Questars may have been sent in for service at some point in their lives, evidence in the form of late examples of an older standard carries more weight than ostensibly early examples of a newer standard.

The Problem

The company sought a number of improvements: a decrease in image shift, a focuser that operated more smoothly, an increase in light throughput, and a reduction in vignetting especially for photography.

Increasing Light Throughput and Limiting Vignetting

The film photographer often saw the effects of the second problem. The narrow dimensions of Questar’s central baffle tube and rear axial port caused significant vignetting for those who were trying to cover the entire 35mm negative.^[16] In its July 1964 booklet, Questar presented a photograph taken with the standard construction as a point of comparison for the newer wide field construction. “Note restricted field of view of Standard model, when camera is close-coupled without extension tubes for work at f/16.”^[17]

The Nature of the Design Change

To allow for smoother focusing with less image shift and a larger exposure area across a 35mm film negative, the company redesigned Questar’s focusing mechanism, internal baffling tube, and rear axial port. The optical design of the instrument remained the same.^[18]

Specifically, both the inside diameter of the primary mirror thimble and the outside diameter of the central baffle tube increased by 0.1095 inches, thereby increasing light throughput. At the same time, the total length of the primary mirror thimble decreased by 0.875 inches, and the length of the central baffle tube decreased by 0.71 inches.^[19] This change may also have reduced the extent to which the forward edge of the central tube cut into the cone of light reflected off the secondary spot.

Between the mirror thimble and central baffle tube, Questar added eight adjustable pads that made the focusing action much smoother than the older metal-on-metal design. The change also gave technicians the ability to minimize image shift by allowing them to fine-tune the operation of the focuser, something that was not possible with the older design.^[20]

Corresponding with the widening of the central baffle tube and primary mirror thimble was a wider rear axial port. The older design called for a hole 0.925 inches in diameter with 32 threads per inch—the same size and threading of the hole that received the male threads of the eyepiece holder on the top of the control box. With the wide field construction, however, the axial port hole grew to 1.1875 inches in diameter with 32 threads per inch—the same size and threading of the male threads on the eyepieces themselves.^[21]

Not only did this change reduce vignetting, but it also enabled a user to thread an eyepiece directly into the rear axial port. One could direct light from the main optics to that rear-mounted eyepiece and make straight-through observations without the use of the built-in diagonal inside the control box, a feature that would have been useful for terrestrial observing.

Not long after introducing the change, Questar was quick to highlight the way in which the wide field construction reduced vignetting in photographs. In its July 1964 booklet, the company featured the change in a full-page spread of photographs. They demonstrated the reduction in vignetting when cameras were coupled closely with the Questar and when they were attached with extension tubes.^[22] And in the price catalog that Questar printed that year, the company also noted that the photographer could now “cover a field about 20% wider on the 35-mm. film, without loss of resolving power, and with better illumination.”^[23]

Announcement

Questar made full use of its advertising presence in Sky and Telescope, Natural History, and Scientific American to announce the wide field construction. It did so as part of its introduction of the modern Field Model, an unmounted version of the 3.5-inch Questar telescope, in the February 1964 issues of these publications. It was the first time that the company ran the same advertising content simultaneously in more than one magazine. Questar wrote that “twenty-one major changes in this barrel and control-box assembly permit a much wider photographic field of view, which now covers all but the very corners of the 24x36 mm. film frame at f/16 without extension tubes. Exposures are two f-numbers faster.”^[24]

Wide Field Construction as a Standard Feature

Throughout the rest of the 1960s and the early 1970s, the company sold fully-mounted Questars with the narrower dimensions as the standard product, and it made the wide field construction available as an upgrade option. As late as its 1972 price catalog, the company differentiated the “Standard Questar, Pyrex Mirror,” which it sold for $1140, from the “Standard Questar, Pyrex Mirror, Wide Field,” which it sold for $100 more.^[25] The company continued to sell units with the older narrower axial port into 1973.^[26]

After introducing the wide field construction, Questar dispensed with the larger flanged focus knob that it included with units built throughout the 1950s and early 1960s. Instead, it adopted a much smaller focus knob for use on all units regardless of whether they had the narrow or wide field construction.

Later in 1973, the company issued a revised product catalog in which it noted for the first time that “all Questars now have the wide-field construction.”^[27]

What could explain the fact that the company offered its older design for nearly a decade after introducing the wide field construction? One possible explanation is the same one that applies to the way in which it transitioned into other newer designs: Questar may have simply wished to use up its existing supply of parts featuring the older standard before implementing the new design across the board.^[28]

Did “standard” narrow field instruments that the company sold into the early 1970s have the same internal construction features—a larger primary mirror thimble and central baffle tube, adjustable friction pads, and so forth—as their wide field siblings? Did they simply lack the larger axial port? One may find it hard to imagine that Questar would have continued using an obsolete 1950s-era internal construction standard that called for metal-on-metal contact between the thimble and main tube in “standard” production units. It seems more likely that Questar used the newer internal design on all instruments featuring both narrow and wide axial ports.

Wide Field Conversions

Before announcing the new design in early 1964, Questar had already made the wide field construction available to owners of older instruments as a conversion option.

In the company’s July 1964 booklet, Questar featured various photographs of birds taken by Dr. R. C. Ashley. All the images “were taken with a full-mounted Questar Photo Model, one of the first to be wide-field modified in 1963. Dr. Ashley... was delighted to find he could take these pictures at f/16 and obtain such wide film coverage, using camera close-coupled without extension tubes.”^[29]

Questar may have offered this new design to its clients even earlier. One collector reported acquiring Questar #1-R-8-339-WA, which was originally built in 1958 and was rebuilt by Questar in 1961. Its updates included the wide field construction, which was indicated as “WA” for “wide angle” in its revised serial number.^[30]

The company continues to offer wide field conversions to older Questars. Able to reuse an instrument’s existing main optics and diagonal, Questar replaces the central baffle tube and backplate assembly, the primary mirror thimble, and the control box housing. During these conversions, Amici prism diagonals have often been the target for replacements with more efficient star diagonals.^[31]

Expanded Commentary on Photographic Technique

In the July 1964 edition of his booklet, Lawrence Braymer discussed telescopic photography techniques in far greater depth than he had in prior editions of Questar promotional literature.^[32] Exasperated with what Modern Photography writer Herbert Keppler described as “self-appointed experts and photographers who would blame the Questar for their own inability to understand the nature of camera vibration, heat waves, and other atmospheric conditions,” Braymer surely did everything he could to address the unique challenges involved in using the Questar telescope for photography.^[33]

Vibration

Although finding a good ground glass was important for achieving focus, Braymer commented that the real enemy of achieving focus were the related problems of mirror slap and shutter shock. Upon making an exposure, the operation of an SLR’s mirror jerked the camera, and its shutter mechanism added an additional jolt. Both movements blurred the resulting exposure. To underscore his point, Braymer included an image of the National Bureau of Standards resolution test chart that demonstrated the effect of this vibration. He added that the best thing to do was to seek out a camera that had the least amount of shutter recoil. A better approach if available was to move the mirror out of the way before attempting to make an exposure.^[36]

Correct Exposure

Braymer also discussed exposure time and the density of a negative as problems that faced the telescopic photographer. The most detailed negative, he advised, was one with the palest markings. Overexposed negatives, on the other hand, were full of dark black tones. In order to get one with the correct exposure, the photographer needed to take important shots across a range of shutter speeds. Those who tried to do precise calculations would miss a lot of opportunities, Braymer warned, so he steered his reader away from asking for exposure tables. There were too many variables to account for. Instead, he simply advised to shoot lots of exposures.^[37]

As his commentary on photographic technique evolved over the course of the early 1960s, Braymer witnessed rapid development in light meter technology. Photoelectric light meters judged light intensity far better than the human eye could, and their use by photographers increased substantially. In 1964, Questar began carrying the Gossen “Lunasix” CdS meter, which earned a reputation among many photographers for its low-light sensitivity and distinctive styling. It was a handheld model that worked better than miniaturized ones built into camera bodies. But one problem for the telescopic photographer was that light meters, which worked best by reading reflected light off nearby objects, were less effective with getting accurate readings from distant objects. Moreover, light meters could not accurately take measurements from ground glass screens. But Braymer assured the readers of his 1964 Questar booklet that light meters were improving all the time and that improved models would become available in the near future.^[38]

Poor Seeing

The final difficulty Lawrence Braymer tackled in his 1964 Questar booklet was the problem of seeing and atmospheric turbulence, which remained the bane of telescopic photographers. Nature was fickle, Braymer complained. One day, the air was steady. The next day, however, it might become turbulent. Seeing conditions could vary hour to hour and even minute to minute. How could one best combat the effects of unsteady air? Since convection caused by the heat of the Sun was responsible for much of the problem, Braymer advised that early mornings and late afternoons were best. Since the direction of light was also important for nature observer, he also advised keeping the Sun to one’s back. In the end, Braymer observed that revolving power was not a strict function of aperture. “Not until we lift telescopes into the vacuum of space will they be completely free of the terrible effects of the hot and agitated ocean of moving gases we must live under and look through.”^[39]

New Photographic Accessories

Along with expanding upon its earlier commentary on technique, Questar also introduced three new or improved accessories that enhanced the experience of the photographer who used the Questar telescope.

Swivel Camera Coupler

Most notable was an improved swivel camera coupler. While the earliest coupler, which the company began offering in the mid-1950s, was simply an eyepiece holder and a machined aluminum adapter with Praktica threads, Questar began developing a swiveling three-part camera coupler as early as August 1963.^[40] The company introduced this “improved basic camera coupling set” in its February 1964 advertisement that appeared in numerous magazines.^[41]

Counterweight

A third accessory addressed the problem that photographers encountered when they attached a heavy camera body to their Questars. As the camera weighed down the rear side of the instrument, the instrument’s motor drive would struggle to operate smoothly. Sometimes it could not pull the camera upward as the mount moved forward. Some kind of counterbalancing weight was necessary on the front end of the scope.

In an advertisement that the company ran in the October 1963 issue of Sky and Telescope, the company depicted its new counterweight accessory for the first time.^[43] In the following month’s issue, Questar described it in greater detail. To ensure the smooth operation of the electric drive during long exposures, “we developed this ingenious counterweight to balance various cameras. Suggested by Questar owner Carl Mathisen, it uses a 1-pound collar of flexible lead-filled vinyl wrapped around star chart. Strips of Velcro (cocklebur type fasteners) lock the collar to tube, which pulls forward as needed for balance. Then the thin bakelite strip, clamped by threaded eyepiece, is pushed down until its own Velcro strip locks tube in position.”^[44]

In the early 1960s, Velcro was still a relatively new product on the market. Patented in 1958, it was not widely known among most consumers during its early years.^[45] By the time Questar introduced the counterweight accessory with Velcro as a fastening material in 1963, it was only natural that the company had to explain what it was and how it worked.

Azimuth Brake

In its April 1966 price catalog, Questar introduced the Azimuth Brake, another relatively simple accessory. It enabled the photographer of terrestrial subjects to advance the film after making an exposure without nudging the telescope out of position and forcing the user to re-aim the telescope. It took the place of the clear plastic indicator over right-ascension setting circle and included all the necessary hardware and tools to make the switch.^[46]

Front Lens Diaphragm

Some enhancements were as simple as a small piece of plastic.

In its 1964 booklet, the company noted that “with every Questar comes this snap-in stop which clarifies views of near objects by blocking those peripheral rays which cannot possibly focus so near.” This flexible ring snapped in place over the threads of the corrector lens cell.^[47] It was especially useful for achieving focus when a Questar was used as a long-distance microscope.

Questar continued to offer its front lens diaphragm until around 1976, when the company featured it for the last time in that year’s edition of its instruction booklet.^[48]

Broadband Coatings

Far more significant was Questar’s use of broadband coatings. In its introductory advertisement in the March 1967 issue of Sky and Telescope, Questar explained the benefits. First, “to the quartz mirror we can apply a broad-band dielectric coating which is hard and durable, and consists of multilayers with varying indices of refraction that increase the reflectivity of the mirror to 99%.” In addition to the primary mirror coatings, both sides of the front corrector lens receive “a VLR (very low reflection) coating.” This application “reduces the light loss at each surface to less than 1/10 of 1%. Again, this coating is extremely tough and actually provides protection to the lens against scratching. It transmits all frequencies of the visible spectrum, and improves the total light grasp by approximately 22%.”^[49]

For a while, Questar had already been supplying custom-built instruments with broadband and VLR coatings to NASA and other agencies of the U.S. government. “Now we have them in stock for immediate delivery” to all clients. “This new phenomenal light-gathering ability of Questar will come as welcome news to the serious amateur astronomer, and to research and industrial users. The photographer will be astonished at the new visibility within shadows, and the sharper contrasts he can obtain for more sparkling pictures.”^[50]

The option for broadband and VLR coatings added $175 to the cost of quartz-mirrored Questars.^[51] The company continued to offer telescopes with aluminum and magnesium fluoride coatings as the standard option.

The company partnered with Perkin-Elmer Corporation, who applied the coatings to optics sets the first decade that Questar made them available.^[52]

At first, the limited guarantee that the company was willing to extend to instruments equipped with broadband coatings suggested that Questar was unsure about the longevity of what was relatively new technology for optics producers at the time. The problem was that the silver coatings naturally lost their reflectivity over time. Moreover, the deterioration of the protective layer over the silver coatings—a process that began most often at the edges of the primary mirror, its weakest point—caused them to tarnish quickly. Although they offered several years of peak performance, broadband coatings were prone to failure more quickly than standard aluminum and magnesium fluoride coatings, and they required expensive replacement over time.^[53]

Questar was well aware of the potential for failure, and it acted accordingly when it set the length of its warranty for the enhancement. In its September 1967 price catalog, the company noted that “broadband and VLR coatings are too new for us to know their life span, but we are guaranteeing them for one year.”^[54] The following year, Questar grew slightly more confident and extended its guarantee to two years.^[55] In its 1971 price catalog, the company reiterated how new broadband and VLR coatings were. But in spite of this, it extended its guarantee to three years.^[56] A decade later, Questar felt comfortable enough to adopt a five-year guarantee for broadband coatings.^[57]

Cer-Vit Primary Mirrors

As late as the mid-1960s, Questar touted the virtues of quartz mirrors, which the company had first offered as a $100 upgrade option in 1957. “Half the Questar telescopes we now produce have mirrors made of quartz,” began its advertisement in the February 1965 issue of Sky and Telescope magazine. The company claimed that the material resisted thermal changes “about 5 times better than Pyrex low-expansion glass. The superiority of quartz lies in this greater stability of the crystal.” Its cost was high but justified by the difficulties involved in producing it.^[58]

In its September 1967 price catalog, Questar introduced another alternative: primary mirrors made of Cer-Vit, a glass-ceramic material invented in the mid-1960s by Owens Illinois. It was a highly stable substance that made an ideal substrate for telescope mirrors, which were prone to distortion with sudden changes in temperature.^[59] It had “essentially no thermal expansion, surpassing even quartz in its stability,” as Questar noted in its first magazine advertisement that described the material.^[60]

Cer-Vit eventually displaced quartz primary mirrors. The older option was missing by the time the company printed its October 1968 price catalog.^[61]

Questar offered a compelling demonstration of Cer-Vit’s benefits by telling the story of a telescope that was in a house that burned to the ground. The instrument was completely destroyed except for its Cer-Vit mirror. “The incredible part is that without refiguring the surface, we recoated it and found its performance unaffected. Its resolution was just as fine as before the fire.” Boasting about its quality, Questar admitted that “we would not have thought of such a drastic method of testing, but it is indeed testimony to the temperature stability of this fabulous material we use to make Questar mirrors.”^[62]

But Cer-Vit was not entirely without its problems. During the manufacturing process, minute bubbles around a tenth or two-tenths of a millimeter tended to form. They would be discovered only after the mirror figuring process was underway. The rejection rate was high and costly.^[63]

Questar offered telescopes with Cer-Vit mirrors until 1980, when the company began using Zerodur as a mirror substrate.^[64] The company continued to offer Pyrex mirrors as the standard option.

Questar did not limit itself to making design enhancements to existing products. During the mid-1960s, the company also introduced new instruments with unique features or significantly greater light grasp.