The Sovietski 6-inch Newtonian reflector.
A blast from the past! The new Russian-made telescope from Sovietski Collection recalls an earlier era - a time when the 6-inch f/8 Newtonian on a German equatorial mounting ruled supreme in the world of amateur astronomy. There are good reasons these telescopes were once bestsellers. They typically offered solid optical and mechanical performance at an attractive price. But the introduction of highly portable, photographer-friendly Schmidt-Cassegrain reflectors in the 1970s, coupled with a general decline in mechanical quality of the era's popularly priced Newtonians, pushed these telescopes to the backwaters of amateur demand. Nevertheless, this Russian import has the potential for reviving interest in the once-dominant design.
The 6-inch f/8 Sovietski telescope is a classic Newtonian reflector on a German equatorial mounting. While lacking the gee-whiz electronics common on today's top-end instruments, it offers exceptional quality at an attractive price. It also sports an impressive collection of standard accessories, including an excellent 8x50 finder, three eyepieces, a 4x Barlow, a set of filters, a solar-projection screen, and more.
Quality is immediately apparent even before you see the telescope. It is shipped in two elegant storage boxes made of heavy, cabinet-grade plywood with finger joints and a clear gloss finish. These boxes have hefty, blackened-steel hinges, clasps, handles, and corner protectors. Fully loaded, they are also heavy (58 and 77 pounds), indicative of the sturdy telescope within. I was certainly impressed by how well the scope is packed using many contoured, foam-lined wooden supports. Nevertheless, once the telescope is assembled it is unlikely to go back into the boxes except for shipping or long-term storage, since there are more than a dozen subassemblies.
As I unpacked the parts, I quickly realized how well the Sovietski scope is constructed, with many machined surfaces, quality metal castings, and a beautiful finish. Even the back of the mirror has been diamond generated! There is very little plastic used in the construction. The heavy steel pier is reinforced both on the top and bottom, where the equatorial head and legs attach. Strangely, its interior was not painted and had developed a thin patina of rust. Antivibration pads are built into the legs.
The optical tube is aluminum and nearly a tenth of an inch thick, so it will not be easily dented. Its interior is finished with circumferential grooving impressed directly into the metal to minimize light scatter, though the black-matte finish had a few slightly glossy areas. Plastic dustcaps are provided for both ends of the tube and for the focuser.
Assembling the telescope is straightforward and takes about 30 minutes. Parts are fastened by a variety of well-designed thumbscrews, all of which are captive, so there is never a question of what goes where. I found fastening each leg to the pier to be a little challenging since the screw must align precisely to engage. After assembly, I noticed that a few joints had slipped, particularly those used to secure the polar-axis elevation. To prevent this it was necessary to torque the locking bolts quite tightly, assisted by an arm built into the most critical nut.
The only tool needed to assemble the scope is a screwdriver (supplied) to fasten a single retaining screw on the dovetail holder for the finder bracket. The dovetail joint allows removing and replacing the finder without having to realign it with the main scope. If returned to the storage box, however, the finder must be separated from its bracket and alignment is lost.
The equatorial mount has some notable features, including preloaded ball bearings on both axes. True to its Russian origin, it can be adjusted up to latitude 70 degrees! Just lift the polar shaft until your latitude is set on the built-in scale, and then tighten the central nut and another on a diagonal brace. The machined-steel counterweight is secured on its shaft by a threaded collar that presses four fingers against the shaft much like a machinist's collet. This is very secure, convenient, and does not mar the shaft. This shaft turns with the telescope, so it is suitable for carrying cameras and the like.
The engraved right-ascension and declination setting circles are easily adjusted. As is typical of German equatorial mounts, the right-ascension circle is not coupled to the clock drive, so it must be constantly reset when the scope is being moved from one object to the next.
When the clock drive was turned on it hummed but didn't move. Close inspection revealed that the 12-volt, 60-hertz synchronous motor was not turning. Standard 110-volt house current is stepped down to 12 volts by a large "power pack," which contains a transformer, fuse, and switch. The fuse is not a standard dimension for North America. While spares are provided, you won't find replacements locally. The power pack connects to the telescope with a 10-meter (33-foot) cable.
Proper voltage was reaching the motor, so I nudged the exposed rotor with a toothpick and it started turning. It's a little noisy. Because the motor stuck about half the time the power was switched on, I contacted Sovietski Collection about the problem. Although the company did not know that the telescope had been purchased by Sky & Telescope for review, the call was handled very pleasantly. The defective motor was returned by overnight express and a replacement was shipped the same way. The company even made a follow-up call to check that everything was satisfactory. No complaints with that kind of customer service!
The polar drive has two slip clutches. One is on the worm wheel so the telescope can be swung around the sky by pushing on the tube. The other is on the motor pinion so the worm can be turned manually for accurately centering objects in the eyepiece - a feature I have not seen on other modestly priced telescopes. Covered ports in the motor housing allow easy access to screws that set the slip resistance of both clutches. The drive had a uniform periodic error of 2 arc-minutes that repeated with each 8-minute rotation of the worm gear.
I collimated the primary mirror, first by sighting into the front of the tube, then while observing a slightly out-of-focus star image at high magnification. The mirror is collimated without tools using hand knobs recessed into the mirror cell, so the tube can rest on its end (during assembly of the telescope) without disrupting the adjustment. Collimation took only a couple of minutes. The diagonal mirror came already collimated, but the solid, well-designed spider assembly also has collimation screws, should adjustment be necessary.
Star testing at high power proved the optics to be quite good. The well-known Double Double, Epsilon Lyrae, was cleanly split and, at 600x, all four components were surrounded by diffraction rings. Views of Jupiter and the Moon were also sharp and pleasing. A knife-edge test on a star showed the mirror surface to be smooth and free of zones, with a good edge. This test also revealed a pattern reminiscent of a paraboloid seen under a Foucault test. Realizing that a spherical mirror looks this way in a star test, I removed the mirror from the tube and performed a conventional Foucault test. It confirmed that the primary was indeed a rather good sphere. Because a 6-inch f/8 spherical mirror produces a one-quarter wavelength error, peak-to-valley, it just meets the diffraction-limited criterion, barring errors from any other sources such as the secondary mirror.
I found centering objects to be quite convenient using the slow-motion controls on both axes. The screw on the declination axis's spring-loaded tangent arm chattered when turned quickly in one direction. Adding a little grease reduced, but did not eliminate, the chatter.
The rack-and-pinion focuser worked smoothly and has several nice features. By grasping both knobs simultaneously and twisting, I found I could adjust the firmness of the motion. The bore is slightly over 1 inches and terminates in a flange with an M44 thread, which is the standard for old Pentax screw-mount camera lenses. This is about the same diameter as today's popular T threads but with a slightly different pitch. The focuser threads were cut rather loosely, however, and I could easily spin a T adapter on for a few turns before the threads locked up. While not ideal, it did make for the easy attachment of cameras. Furthermore, because of the focuser's novel design, a conventional 35-mm camera body is within focusing additional adjustments.
To use standard 1 -inch eyepieces, an adapter is screwed onto the M44 thread. The adapter and the Barlow lens both have a thumbscrew bearing on a recessed ring, which clamps the eyepiece without scoring or scratching. I have seen this welcome design only rarely, usually on expensive equipment.
Three 1 1/4-inch eyepieces come with the scope; 15- and 42-mm Kellners and a 25-mm Plossl. All worked well, though the apparent field of the Kellners is narrow relative to modern designs. In fact, the actual field of the Plossl is about the same as that of the 42-mm Kellner despite offering a nearly 70 percent increase in magnification. The 4x Barlow was a different story. It exhibited noticeable lateral color, and image quality was good only at the center of the field.
The scope comes with six glass filters. They include cyan, yellow, magenta, and red, as well as two neutral-density filters - one for the Moon and the other for solar observing when teamed with a supplied off-axis aperture stop. Each filter has a plastic body and clips to the eye end of the eyepieces. They have a clear aperture of only 1/2 inch, so they cover part of the eye lens of the Plossl, restricting some of the field.
In the interest of eye safety I did not test the solar filter, and I recommend that others avoid it as well. There is always a chance the filter may crack when heated by concentrated sunlight. I suggest that solar observing be done using the supplied projection screen, which has clips to hold sketching paper. The manual does not show how to attach it, so it took me a minute to figure out that it rides on the counterweight shaft. The telescope is rotated and slid slightly from the balance point until the eyepiece is in line with the screen. While the setup is convenient for group viewing, I am concerned that no lens cap is provided for the finder. I always cover a telescope's finder when viewing the Sun to prevent the unwary from taking a peek.
The 6-inch Sovietski Newtonian is an excellent telescope at a remarkable price, especially considering its features, accessories, and quality.
Sovietski 6-inch telescope
Russian-made 6-inch f/8 Newtonian reflector on a German equatorial mounting
Sovietski Collection 3450 Kurtz St, Suite C San Diego, CA 921100 Phone: 619-294-2000 Price: $699
RELATED ARTICLE: Clock-Drive Modifications
As explained in the accompanying text, the balky drive motor in the Russian scope was the only weak link in an otherwise very strong chain. Designed for the European community, the original drive had a 12-volt 50-hertz motor and a power pack rated for 220 volts AC. For the North American market, the system was changed to a 110-volt power pack and 60-hertz motor, and the original "50Hz" engraved on the drive housing was rather crudely changed to read "60Hz." While low-voltage AC motors offer some safety advantages in damp and dewy conditions, they are not commonly found in telescope drives, and they rule out using conventional accessories like drive correctors.
To improve the reliability of the Russian telescope's drive, eliminate the bulky power pack, and restore the option of using a standard drive corrector, I made a simple modification. The Russian 0.2-rpm motor was swapped for a 110-volt 60-hertz synchronous motor manufactured by Hurst Motors, P.O. Box 326, Princeton, IN 47670 (phone: 812-385 -2564). Because Hurst's 0.2-rpm model is a built-to-order unit, it currently costs $183.50 direct from the manufacturer. However, according to Hurst's Bill Johnson, the motors cost considerably less from dealers. Indeed, I found one in stock for $72.70 at Electro Sales Co., Inc., 100 Fellsway West, Somerville, MA 02145 (phone: 617-666-0500). When not in stock, the motors can take up to 8 weeks to order.
The conversion took about two hours, with half the time spent making a new bracket out of 1/8-inch aluminum plate using a hacksaw and file. The original bracket could also be easily modified to accept the new motor, even by someone with more thumbs than fingers. The drive gear fits on the new motor without modification. A switch and pilot light from Radio Shack cost less than $5, and I scavenged a power cord from an old appliance headed for the trash.
This change offered two additional benefits. The Hurst motor shaft is more rigid than that on the Russian motor, and while it didn't change the drive's total periodic error, it did smooth out minor "jumps." Unlike the original, the Hurst motor is reversible, making it suitable for use in the Southern Hemisphere.
A mechanical engineer with more than three decades of experience as a telescope maker, GEORGE EAST frequently reviews products for Sky & Telescope.
|Printer friendly Cite/link Email Feedback|
|Publication:||Sky & Telescope|
|Date:||Dec 1, 1997|
|Previous Article:||Europa: distant ocean, hidden life?|
|Next Article:||An asteroid's remarkable orbit.|