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Criterion RV-6 Dynascope®
"these introduced many of us to visual astronomy"
"these introduced many of us to visual astronomy"
The RV-6's illustrated here are from Criterion literature and an RV-6 that is in Company Seven's museum collection of telescopes.
Preface In January 2008 Company Seven added a Criterion RV-6 Dynascope to our museum collection. The RV-6 Dynascope is a six inch (6") aperture 1,270mm focal length f/8 Newtonian reflecting optical tube assembly mated onto the 'Dynascope' model German Equatorial Mount. This was a commercial product manufactured by Criterion Manufacturing, Inc., among the first few U.S. based producers of complete good quality amateur telescopes who operated from the 1950's to the 1980's. The instrument was geared to the amateur and school markets with a goal of maintaining a modest price.
Right: The Criterion Dynascope RV-6 Telescope of 1962. The tube assembly is painted dark gray, the pier is silver gray (26,234 bytes).
Company Seven had been on the lookout to acquire an RV-6 for display since we know it is among the landmark telescopes that gave thousands of people their introduction to visual astronomy. The founder of Company Seven fondly recalls seeing the Moon through the first telescope he ever encountered, a 6 inch reflector:
The particular unit acquired by Company Seven was represented to us as being "in excellent condition", complete and fully documented even with the original Invoice dated December 14, 1962. The original cost of the set was $194.95, plus 3-½% State Sales Tax, and with an extra Cord added at the last minute this amounted to $205.00.
Above: the Criterion RV-6 telescope in the Company Seven Museum Collection. This instrument is complete as it was picked up by the
And if it was provided with the telescope, then the instruction manual was not provided to us. Since our general policy is to conserve antiques, we display this telescope among our collection at our showroom cleaned but otherwise not restored. However, for those who are interested in seeing how a telescope like this comes together, please browse our Criterion RV-6 Dynascope Restoration Gallery where Mr. Tom McDonough shows us in a series of images how over the course of several months he disassembled, refinished and upgraded his RV-6.
Background: Criterion Mfg., Inc. The Criterion Co. was established at 331 Church Street, Hartford 3, Connecticut by Mr. John Krewalk, Sr. In time it became Criterion Manufacturing Company, Inc. His son John J. Krewalk (b. 1950) would in time come to work for the company too. The sales invoice provided with the RV-6 owned by Company Seven indicates the telephone number then was 247-1696, and their Cable address was "CRICO".
The first telescope offered by the Criterion Co. was the 1954 model 1.6 inch (40mm) aperture f/25 achromatic refracting telescope. This included three eyepieces providing 40, 80 and 111x. Resembling a walking stick it was provided on a simple alt-az (altitude and azimuth, or pan and tilt) mount and tripod standing about 5 feet tall and selling for $26.95. Some months after the 1.6 inch telescope was made available Criterion announced the first 'Dynascope' a four inch (4") Newtonian Reflecting telescope that sold with three eyepieces in 1954 for $44.95 plus shipping. As telescope mounts and accessories were improved then the costs escalated accordingly. Do not overlook the fact that telescopes such as these were still rather costly 'luxury items' at a time when the monthly rent might be $150 per month or less. And this was well before credit cards so by 1956 Criterion (among other telescope makers) offered time payment plans of up to twenty four months. Some of us at Company Seven still recall still offering simple payment plan options for customers ordering a Questar telescope (also introduced in 1954) as late as the mid 1980's.
By 1955 the first commercial 6 inch f/8 Newtonian telescope became available, made by competitor Edmund Salvage Co. this no doubt put pressure on Criterion to respond. And Criterion may have already had their response in the works since in the December 1956 issue of Sky and Telescope they announced the new series of Newtonian telescopes. This would initially include the Dynascope 6 inch with either a German mount with wood tripod or a deluxe German mount and with a massive steel pier, and the line grew to feature models of as large as 16 inch aperture. Resembling the flared bell of a trumpet the deluxe massive pier-mounted 6 inch Newtonian telescope cost $475!
The RV-6 Dynascope Several versions of the Dynascope 6 telescope were produced but the RV-6 that would come to dominate its class would not appear until January 1959 when Criterion's two page spread in Sky and Telescope revealed it:
"NEW! LIGHTWEIGHT ELECTRIC 6-INCH DYNASCOPE.
Here is 6-inch performance at a 4-inch price! This scientifically designed new Dynascope offers all the essential features for superior viewing at a cost within the reach of any serious amateur. Constructed of lifetime material and engineered for maximum stability, yet is extremely light. And look at these other quality features in this exciting new instrument:
Model No. RV-6 COMPLETE FOR ONLY $194.95 F.O.B. Hartford, Conn. Shipping Wt. 55 lbs. Express Chgs. Collect".
Above: The portion of the January 1959 two page advertisement that introduced the Criterion Dynascope RV-6 telescope.
After finally adding a Criterion RV-6 to our own collection Company Seven observed that almost all the early images that we have seen published advertising the Criterion RV-6 show:
2. the optical tube shown is not a RV-6. These early images may have shown a mock up of the RV-6 or a poorly scaled image,
3. the counterweight shaft above and then below the counterweight are different diameters,
4. the counterweight shown would be inadequately light to balance an actual RV-6.
* The "rotating tube" mentioned in these RV-6 advertisements is a term that is by todays standards misleading. The optical tube is held onto the German mount saddle plate by means of two hinged clamping mounting rings. By loosening the ring clamps it was possible to rotate the telescope tube so that during the course of observing one then another objects in various areas of the night sky, the focuser with eyepiece could be rotated to a more accessible position. In practice, the early RV-6 tube exteriors where very textured, and this made it impossible to rotate the tube unless the ring clamps were loosened almost fully. By the 1980's rotating ring hardware sets were available for amateur Newtonian telescopes that were more practical moving smoothly and with clutches for adjustable drag or locking into place, and these were more precise at keeping the telescope tube optical axis more closely parallel to that of the mount's axis of rotation.
The Criterion RV-6 was delivered or it could be picked up at the factory assembled with the optics collimated. It was provided with a 6x 30mm Finderscope, with a rack and pinion 1.25 inch Focuser to accommodate the customers choice of three eyepieces, with electric motorized clock drive, Right Ascension and Declination Setting Circles, and a complete money back guarantee.
The price of $194.95 in 1959 had about the same buying power as $1,419.00 in 2008. Annual inflation over this period was about 4.13%. So the customer could choose to pay the instrument in full, or pay a deposit with the balance paid in monthly installments over 6, 12, 18 or 24 months.
Optics Several optical shops became established in the late 1940's and early 1950's founded by craftsmen who learned their skills working in the armaments industry. These shops produced consistently good industrial quality optics at a comparatively modest cost, and it was these companies who made the optics sold to Criterion as well as to its competitors including Edmund Scientific, and Cave Co. Our Criterion RV-6 Dynascope Restoration Gallery with images by Mr. Tom McDonough shows a certification label of one of these subcontractors (UPCO OPTICS) attached to the Primary Mirror. Criterion would continue to source their optics design services and components from optics fabricators in the USA until Criterion began to explore ways to make optics for their "Dynamax 8" catadioptric telescope introduced in 1971.
Right: Image by Mr. Tom McDonough showing the "UPCO OPTICS" label on the back of his Criterion Dynascope RV-6 Primary Mirror (64,089 bytes).
A good measure of the success of the Criterion telescopes of this time were the high performance of their optics. While meeting the optical prescription of the proper curve is important, it is critical that the surface be polished to be consistently smooth as well. In all fairness it is not as complicated a matter to figure (grind and polish) the Primary Mirror of a reflecting telescope at f/8 so that it will perform well enough to impress most buyers as it is to make a mirror do well at faster ratios of f/6 or f/5 since the mirrors of an f/8 reflector can made almost spherical. And the comparatively long focal ratio means the telescope can provide stunningly clear images across the field of view even when operating with comparatively simple eyepieces. The Criterion Primary Mirror substrate is Pyrex® which is arguably better than necessary for a small f/8 telescope, but it is a choice indicative of caring by management and not of pinching pennies.
It may be that when we were young we were naive, or it may be these were well made optics - that truth is: this will not matter since
these telescopes served their purpose, and did so affordably.
Right: click on this image to see the full page advertisement of 1960 showing the Criterion Dynascope RV-6 Telescope apparently with a white OTA (60,316 bytes).
Eyepieces The brochure accompanying our RV-6 listed these as choices of Achromatic Ramsden and Orthoscopic eyepieces: AR 18mm - 65x, AR 12.7mm - 100x, AR 9mm - 150X, OR 6mm 200X, or OR 4mm 320X. The Carl Zeiss designed Achromatic Ramsden (sometimes termed 'Modified Achromatic' and similar to the Kellner) are good economical general purpose eyepieces when made well. While the Orthoscopic (another Zeiss design) may be highly regarded for its uniformity of magnification across the field of view, combined with very good to superb contrast and definition thereby making it a good choice for observing planets for example. The telescope in Company Seven's collection came with the original three 1.25 inch diameter eyepieces wrapped in tissue within one cardboard box.
Left: Original eyepieces provided with the RV-6 Dynascope in our collection:
Click on the image to see enlarged view (100,004 bytes).
Click on the image to see enlarged view (100,004 bytes).
There were other eyepieces sold for the Criterion telescopes, these might bear the their Cable address "CRICO" as a trademark. The offerings included some upscale Erfle eyepieces. It is surprising to find this affordably priced telescope was furnished with well constructed eyepieces and of the larger 1.25 inch diameter since at the time and throughout the 1960's into the 1980's most other 'beginner telescopes' were provided with 0.965 inch diameter eyepieces. And it was rare that amateur eyepieces would be found to have been mechanically as well made as these. The interior of each barrel is painted anti-reflection black but we do note however, this telescope's Criterion eyepiece barrels were not fashioned to accept thread-on filters.
The OTA Mechanical Aspects The success of the optics is in part made possible by the well engineered mechanical components that hold the Parabolic Primary and Elliptical Secondary Mirrors precisely and rigidly in their proper place within the 50 inch long optical tube. It was not uncommon for a person to collimate the telescope once and with some care in transport would never again have to make an adjustment of the optics to regain a nominal collimation.
The optical tube is made of Bakelite (pronounced 'Bay-Kah-Lite') tube. Bakelite is the world's first plastic, a formulated synthetic resin named after Dr. Leo Baekeland the Belgian-American chemist who invented it around 1909. It is thermally stable, resistant to moisture, lightweight, rigid and non-conductive; these properties made it a natural choice for making insulators, electronic circuit boards, and a thousands of other components where light weight and rigidity were a must. By the 1980's the use of phenolics for making consumer products declined due to the cost and complexity of their production, and also due to their brittle nature. Today some companies offer Bakelite components for specialized uses or for the nostalgic appeal. The Bakelite used in to make the RV-6 optical tubes were treated with a highly textured finish originally in a dark gray, and later in a smoother textured black, and even later a white painted finish. The interior of the optical tube, along with all the machined components that protrude into the optical tube are finished in an anti-reflection black.
This model RV-6 has no protective metal trim rings attached onto the ends of the optical tube. We have seen older and contemporary models provided with these decorative metal rings, they also help to protect the ends of the Bakelite tube from wear and tear. Regardless of lacking these rings this RV-6 has survived the decades well no doubt due to some careful handling by the owner.
The optical tube was provided with a bolted on metal plate with the serial number engraved, while the mount similarly is furnished with a riveted metal plate stamped with its own serial number. The RV-6 in Company Seven's collection for example bears OTA No. 2746 while the mount bears No. 2870. This leaves us wondering if some 124 or so of these mounts may have been either sold separately or sold as an upgrade choice for other Criterion telescopes?
The other components of the telescope (Focuser, Secondary Mirror Spider and Mirror Holder, etc.) are machined of steel or brass, with machined castings for the counterweight and for major components of the German Mount head.
The Primary Mirror is held at the bottom of the optical tube within a floating cell, a holder that does not rest directly against the optical tube but is suspended above a lower metal casting by three bolts, these bolts adjust the tip tilt of the mirror. There is space all around the rear and sides of the Primary Mirror and this accommodates air circulation that will help to acclimate the glass mirror to ambient temperature. We note older RV-6 models have a more closed Primary Mirror cell arrangement.
This RV-6 telescope is provided with the four vane Spider to hold the Secondary Mirror firmly in place inside the telescope optical tube and in line with the rack and pinion focuser. This mechanism includes adjustments to center the Secondary Mirror in the optical tube by tightening or loosening the four nuts 90 degrees apart on the optical tube. And it provides adjustments to tilt the Secondary Mirror relative to the Primary Mirror and Focuser, and also to adjust rotation of the Secondary Mirror.
We have seen earlier examples of the RV-6 telescopes that were provided with a simpler circular Spider. This Spider attached to the optical tube with one bolt to the inner wall of the optical tube. This design reduced the diffraction effects that come about when a blade is inserted in the light path, and does this better than conventional Spider arrangements. However, the circular Spider was more awkward for amateurs to work with, and subject to working loose thereby leaving the Secondary Mirror rotated from its nominal position. We believe this may be the reason why later models (as the one in our collection) come equipped with more conventional four vane Spiders.
Earth's Motion And The Equatorial Mount
The Earth rotates about its axis and so celestial objects appear to move across the sky in arcs as the Earth turns. This period of 23 hours 56 minutes 04.09053 seconds is called the sidereal period, or the period relative to position of the stars overhead. The sidereal period is not exactly equal to one 24 hour day because by the time the Earth has rotated once complete revolution on its axis it has also moved along the path of its orbit around the Sun. Because of this the Earth has to keep rotating for about another 4 minutes before the Sun seems to be back in the same place in the sky that it was in exactly a day before. As the Earth rotates in space the celestial objects overhead appear to move in an arc across the sky.
Left: Movie demonstrating Earth rotation. This is in Quick Time movie format courtesy of NASA (3.0 megabyte file).
For an observer located in the Northern Hemisphere these objects appear to rise in the Eastern horizon, then gradually move in an arc up and right across the sky peaking towards the South, and then continue moving to the right and down towards the Western horizon. For an example look at the Moon rising low in the sky though trees, at 1X with the naked eye one can see the Moons apparent motion - actually it is us on Earth who are rotating. So imagine trying to keep a telescope on target when operating at magnifications high enough to see the Moon close up; 80 to 100X or so. Then imagine keeping up with a planet at the 200X or more that we recommend! One comes to appreciate having a platform that can keep the telescope on target.
Right: Color image of the 1962 Criterion Dynascope RV-6 telescope in Company Seven's Museum Collection. Note the gray painted tube assembly with white Criterion Finder (23,751 bytes).
And for astrophotography where one is attempting to record the relatively faint, deep sky objects on film or CCD requires time exposures on the order of minutes to an hour or more. This makes it impractical to attempt time exposure astrophotography with an alt-azimuth stand or a conventional camera tripod since it is impossible to precisely move a manual Alt-Azimuth mount so that stars do not appear blurred on the film.
The solution to the limits imposed by the manually guided Alt-Azimuth mount is the motorized Equatorial Mount; a platform which can track in one smooth motion in exactly the opposite direction of the Earth's rotation and at a similar apparent rate. Platforms such as this came about in order to permit the photography of celestial objects without having to buy a more costly and bulky conventional equatorial mount. Supported by a portable steel pier the entire platform with the telescope are rotated left or right, then tilted up or down to "Pole Align" its axis of rotation paralleling that of the Earth's axis of rotation. The more accurately one aligns a platform with the Celestial Pole, the more accurate is the tracking but an alignment to within two degrees or so of the true celestial North Pole is adequate for visual observing with a telescope like this RV-6.
The three cast aluminum Legs that bolt onto the Pier Post of this RV-6 incorporate wide pads at each tip. These are attached to the tip by a threaded bolt so that each pad may be extended or retracted to facilitate a finer adjustment for Pole Alignment than could be achieved by adjusting the mount head alone.
Once the German mount platform is "pole aligned" then the motor can be turned on permitting the telescope to be pointed to the area of sky and track on a target as the Earth rotates. A mount such as this allows the observer to focus on an object free of concerns about keeping the telescope on target, it facilitates sharing a telescope with many people, and it can be an economical way to start into astrophotography.
Among the factors that made the Criterion telescopes a success was the German Equatorial Mount made of machined and cast aluminum, steel, and brass. This was equipped with their motorized Right Ascension Drive with which one could track objects across the sky; this made it more comfortable to observe, easier to share the telescope with others, and opened the possibility of astrophotography. Called the 'Dyn-O-Matic', the system consisted of several components:
The Glory Days
Criterion became very successful with the lines of telescopes that they developed. Over the years under the original management they added more sophisticated and larger models. Their numerous ads appeared in periodicals including: Sky and Telescope, Review of Popular Astronomy, and Science Digest. By mid 1961 the sales of the RV-6 eclipsed those of their 4 inch telescope and the advertising shifted gradually to focus on the RV-6. Through the 1960's astronomy fever was at a peak since the space program was in full swing with real heroes and a national purpose. People and screen writers had imagination; television programs about astronauts, space and a bright future were on in prime time including 'Outer Limits', 'Twilight Zone', 'Lost In Space', 'My Favorite Martian', 'The Jetsons' cartoon, 'I Dream of Jeannie', and of course 'Star Trek'. NASA's Apollo 11 landed on the Moon on July 20, 1969 and not long afterwards the Criterion RV-8 teleswcope was announced in October selling for $399.95. Soon the focus of advertising shifted to these larger models. Some of the demand by the public for larger telescopes might have been because increasing sky light glow from development and air pollution were reducing the transparency of the suburban skies so that amateur astronomers needed larger telescopes to show more to retain their interest in the hobby.
Left: Old Glory salutes the launch of Apollo 11, the first Lunar landing mission. The Apollo 11 Saturn V space vehicle lifted off from Kennedy Space Center's Launch Complex 39A at 9:32 AM EDT July 16, 1969 with astronauts Neil A. Armstrong, Michael Collins and Edwin E. Aldrin, Jr. On July 20 their Lunar Landing Module descended onto the Moon touching down at 4:17:40 PM EDT (20:17:40 UTC). Many people around the world paused to share this televised moment live, and many more stayed up to watch Neil Armstrong step off the Lander and onto the Moon at 10:56 PM EDT (2:56 UTC) where he uttered "That's one small step for [a] man, one giant leap for mankind". Rarely since then has the world been so similarly united. Audio file is .mpeg format 83,968 bytes. The image size 5,840 bytes.
As interest in space exploration and in the Moon landings rose, so did the demand for good quality amateur telescopes increased. While competing affordable refracting telescopes were coming into the market too, some surprisingly well made in the 1960's including Tasco, Unitron, etc., there was still a demand for light gathering power and or the economy and overall value that the 6 inch Newtonian telescope provided. And the RV-6 prospered.
The Demise Of Criterion RV-6
As images from space and the pace of life quickened through the later 1960's, there was less and less that could be left to the imagination. A glimpse of Saturn appearing with modest details no longer had the impact on one coming of age in the 1960's and later that it might have had in the 1950's and earlier. In the Fall of 1968 Criterion introduced the RV-8, an 8 inch f/6 telescope with a scaled up Dynamax German Mount selling for $399.95. With about a 50% increase in light gathering power over the RV-6, a proportionate increase in resolving power, and sharing the same physical length of about four feet, the RV-8 too became an instant success.
But events were conspiring against Criterion, and management failed to grasp these in time to save the company as it had been:
2. A company on the opposite coast had been gaining experience and perfecting the relatively economical mass production of a compact, low maintenance telescope optical tube design. The tube assembly could be made to be as little as ¼ the physical length of a comparable Newtonian optical tube assembly. And the shorter tube length made it possible to provide the telescope on a lighter weight and more intuitive Fork Mount. This company was Celestron Pacific who specialized in the development of the Schmidt-Cassegrain telescopes from 10 inch to as large as 22 inch for government and industry. The company had two people who are largely responsible for their success: Tom Johnson, the optical designer and Alan Hale the business brains of the outfit. By 1970 Celestron struck gold in the amateur market with their introduction of the original 'Celestron 8', a 23 lb. integrated optical tube and fork mount.
Right: The basic Celestron C-8 Schmidt-Cassegrain telescope with Fork Equatorial mount of 1970; weight 23 lbs. (image size 157,343 bytes).
Criterion either failed to notice the Celestron products in time, or maybe they simply lacked access to an optical source who could consistently make optics that could compete with those of Celestron, but it appears as though Criterion was waiting at the Bus Station when this Ship came in.
3. By 1977 another West Coast company introduced telescopes made off shore including their own 6"f8 Model 591 Newtonian Reflector with a motorized German Equatorial Mount. And later they hired employees with good Newtonian telescope making experience from another recently failed venture and began to produce telescopes that at first resembled the Criterion reflecting models, their first were the Meade 6"f8 Model 628 and 8"f6 Model 826. The Meade Model 826 is such a fine Newtonian that Company Seven keeps one of these too in our museum collection alongside our RV-6. But soon after Meade Instruments went into the business of making these telescopes they improved upon them rapidly. And they employed techniques and business acumen that provided these telescopes were priced competitively with the Criterion.
By the Spring of 1977 the RV-6 prices had increased to $249.00. This seemed to be a fair price, but now it too was having to compete with Celestron's "C-5" 5 inch Catadioptric telescope. The bulk, weight and comparative complexity and higher maintenance of the Newtonian offset the price advantages for most observers, regardless of the fact that the RV-6 could show more sky, and show it better than any C-5. And as prices rose, the RV series lost its appeal to those who were astute.
In 1980 Meade Instruments joined the SCT fray with their own 8 inch the Model 2080, and later a 4 inch Model 2040, and this put additional pressure on Criterion. The Meade and Celestron telescopes could interchange a broader range of accessories than those of the Dynamax series, and Criterion never matched the output of these competitors for variety or quantity of accessories, and this too diminished the attractiveness of the Dynamax to the informed shopper.
And the poor condition of the US economy particularly during the Carter presidency meant there was more and more competition for fewer sales.
In 1981 Criterion still operating in East Hartford, Connecticut ceased to function as an independent company after being sold by the Krewalk family to Bushnell Co. Bushnell were based in Pasadena, California and were a wholly owned division of Bausch & Lomb, Inc. By March of 1982 the last advertisement for the RV-6 appeared offering the telescope for $359.95. This price was higher than the price of the more attractive Meade 6 inch (f/5 and f/8) telescopes. After having been in production since 1959 the RV-6 were no more.
The Demise Of Criterion The remnants of Criterion continued production after the Bushnell and Bausch & Lomb trademarks. The product line and policies had been so eroded in the eyes of management at Company Seven that we had no interest in picking up their products even as we rode the crest of 'Comet Halley' from 1984 to 1985. We sensed this company was being directed by corporate people who knew the cost of everything, but the value of nothing.
By this time imported instruments (especially from Japan) were gaining U.S. market share, and several U.S. based makers of telescopes were sending more and more work to off shore. The manufacturing of telescopes and optical products continues in East Hartford until in December 1997 when Bausch & Lomb decided to close this facility and focus on other high tech consumer items: sunglasses, contact lenses, and such. And by this time all US manufacturers of good amateur telescopes who operated from the 1950's through the 1970's had gone out of business with the exceptions of Celestron International and Meade Instruments. And neither Celestron or Meade would survive as independent US manufacturing companies beyond 2007. Celestron was sold to a Chinese manufacturer, while Meade exported production to Mexico and China; other artifacts of the unfortunate George W. Bush Presidency and of sheer capitalistic greed operating at its short-sighted norm.
There is one noteworthy U.S. company who have endured since 1954, and this is Questar Corporation of New Hope, PA. Known for making the 'Rolls-Royce' of precision compact telescopes, they have endured since 1954 by not tampering much with what makes a Questar great - and by not having to answer to Wall Street.
Criterion RV-6 Dynascope Specifications:
The Internet continues to evolve and bring the world closer than ever, among the benefits are all the resources that helped one to not only find these telescopes used, or rare parts to make restore them, but also literature. Here are Criterion documents scanned by the host of this site:
This is the scanned copy of original document* from Company Seven's Archives (717,437 bytes with our Cover Sheet), the telescope this document accompanied also resides in our collection through the generousity of E. De La Pena.
*Curiously enough there were two copies of Page 5 one poor and another better, this may be as it was provided by the factory. We provide only the better of the two pages in this .pdf.
If you are a novice who has acquired a telescope such as this then instead of relying on this manual alone, we urge you to look for better written contemporary observational astronomy guide books (Nighwatch for example) and affiliate yourself with an astronomy club.
|We invite you to visit our showroom near Washington, D.C. to see our RV-6 first hand or contact us by E-Mail to firstname.lastname@example.org, or by telephone 301-953-2000. The showroom is open Monday to Friday 11 am to 6 pm, Saturday 11 am to 5 pm. We are closed on Sundays, on U.S. Holidays, and from 25 December through 1 January inclusive.|
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