Review of the Rumak "Intes Italia Challenger 180" Telescope“ 

This review concerns a telescope produced and marketed in the 2000s. At the time, the Ghisi family, owners of the astronomical shop “Il Diaframma,” had created the Intes Italia brand with the intention of giving a more modern aesthetic look to the spartan Russian telescopes.

I tested a Rumak 180/1800 telescope in 2003, when I was part of the Technical Staff of the monthly magazine “Le Stelle”, at the time directed by Professor Margherita Hack and the late Corrado Lamberti.

I share my past impressions below, hoping they may be useful to some enthusiasts.

If I had to rank the instrument most beloved by amateur astronomers in the 1990s, the Schmidt-Cassegrain would undoubtedly rank first. This optical configuration, introduced in 1954 by Alan Hale and Tom Johnson and launched on the market in 1966, after various refinements, has garnered the acclaim of many observers over the years. Its compact optical configuration is suitable for versatile use, although it doesn't excel in any one area.
Increased light pollution in our country is driving more and more amateur astronomers to observe and image solar system objects. Many, unable to afford expensive apochromatic refractors, feel the need for an affordable instrument that can provide high-contrast images, be compact, and allow for occasional travel to observe deep-sky objects under the clear skies of high mountains.

The Rumak I'm discussing in this article combines all these features and offers even more than the Schmidt-Cassegrain configuration. The first thing that catches the eye is its meticulous design. Russian manufacturers have never excelled in this area in the past. Their products have always been appreciated for their high-performance optics, but certainly not for their tubes and finish: the former are spartan and heavy, the latter poorly crafted. Lately, however, perhaps also thanks to market demands and the requests of Italian importers, significant progress has been made: the Challenger's external parts are well anodized, while the tube, with its finally modern design, is covered with a layer of white paint; most of the mounting screws are hidden from view. The meniscus is protected by a cover that fits perfectly with light pressure, while the interior of the tube is beautifully opaque. Also on display is a 10 x 50 matte black finder scope, equipped with a 5° Plossl eyepiece and a mount for mounting an illuminator. Of good optical quality, it features a spartan but effective focusing mechanism, which is achieved by rotating the eyepiece. The Intes Italia Challenger 180 adopts the classic Russian Maksutov optical configuration, created and perfected according to the Ruuten–Maksutov (Rumak) scheme, in order to provide greater brightness and greater correction of aberrations, a weak point of all classic Maksutovs.
The central obstruction of the instrument is equal to 33% of its diameter. The spherical meniscus is made of K8 glass with multiple anti-reflection coatings, held in the cell by a ring that allows for uniform pressure, thus displaying very regular diffraction images. Unlike the menisci fixed by multiple screws, the mirrors, also spherical, are made of LK-5 glass aluminized and protected by an Al-SiO2 coating; remember that the secondary is separated from the meniscus and collimated separately. The linear field is 40 mm, the theoretical resolution is 0.68, while the focal ratio has been modified for more universal use and stands at the classic F/10 of SCs.

In terms of dimensions, the Russian Maksutov is remarkably compact: the tube length is 730 mm, the external diameter is 200 mm, and the net weight is 7 kg. Unlike traditional Maksutovs, the Challenger Intes uses a two-inch Crayford focuser with 35 mm of travel, which does not involve movement of the primary mirror, thus avoiding aberrations, image drift, and collimation errors. In my tests, it proved to be very precise, especially when making focus corrections at high magnifications. Due to its decidedly external focus, the use of a diagonal and, if necessary, a adapter is mandatory if observing through 31.8 mm eyepieces.

I tested the instrument in the Lombardy Prealps at an altitude of 600 meters, in the presence of sufficiently low light pollution: let's say under a magnitude 5 sky. First, I adjusted the secondary using a LaserMax TLC 1-800 collimator, later refining the operation by analyzing a star diffraction ring at high magnifications (I aimed at Aldebaran, Alpha Tauri, magnitude 0.86). The image, once adjusted, revealed very sharp and uniformly bright diffraction rings.

Testing the optics on some stars in the winter sky, I found this configuration to be more accurate than the traditional Maksutov design. This is because the secondary mirror was not created by aluminizing the central area of the meniscus, but by machining an independent mirror. The designer is therefore able to treat the secondary separately and then combine it, with greater precision, with the primary mirror and the meniscus. The downside is that the support that holds it, equipped with a dew shield, creates a greater obstruction than the traditional design.

 In any case, during my sky tests, I only found a very slight spherical aberration and a slight edge coma. These shortcomings do not affect deep-sky visual observations, as the observer can tolerate a slight edge defect in favor of excellent optical processing. Moreover, this instrument is not intended for deep-sky photography; in this field, the prevalence of apochromatic refractors is unquestionable.

In high resolution, however, the optical quality, compensating for the obstruction, does not make one regret a refractive instrument of a slightly smaller diameter. As mentioned, the Rumak design differs from the traditional Maksutov by the presence of a collimable spherical primary and secondary lens, with a focal length of 1800 mm: this makes it suitable for deep-sky observations as well. It therefore seemed reasonable to compare it with the classic 203 mm Celestron. On a particularly clear January evening, I pointed the two instruments at the Orion Nebula and found that there were no notable differences in brightness in the images provided, a testament to the excellent reflection of the Russian optics compared to a good commercial Schmidt-Cassegrain. The trapezium stars in M42 were also more contrasty in the Celestron Challenger 180. I also noticed the same thing when observing other objects in the Messier catalog, such as M35 in Gemini; M36, M37, M38 in Auriga; M41 near Sirius; and the Double Cluster in Perseus. Observing the galaxies M81 and M82 in Ursa Major was also fruitful; in this instance, the Celestron showed a slightly brighter image, but the Challenger's superior contrast allowed the faint galaxies to stand out from the background sky.

I also observed M51 and M101, visible as distinct patches of light. Under a clear, high-mountain sky, performance would obviously have been better, but unfortunately, the weather conditions in January prevented me from fully exploiting the instrument's potential.

 

On an evening with average seeing, I again compared the Challenger 180 with the Celestron C8; furthermore, to have a fair comparison method for observing low-contrast details, I also used a splendid 102 mm fluorite refractor from Vixen.

The instrument that suffered most from the atmospheric conditions was the Schmidt-Cassegrain, followed by the Russian Maksutov. Jupiter's disk was at times severely disturbed by variations in seeing, but in moments of less turbulence, I observed, albeit with difficulty, the South and North Equatorial Bands (SEB and NEB), the North Temperate Band (NTB), and the North North Temperate Band (NNTB); furthermore, the faint colorations of the gaseous bands of the Solar System Giant were clearly evident. The images revealed by the Fluorite refractor were obviously calmer.

Saturn, in subsequent series, aided by a light haze that calmed the turbulence, exhibited the Cassini division, the subtle color differences in the B ring, and the discontinuity near the A ring. The maximum magnification I could exploit with the Challenger 180s before the images decayed was 360x (7.5mm Plossl). In this case, the greater resolution of the Celestron and Intes made itself felt compared to the Vixen refractor.

 

Ultimately, the Maksutov Challenger 180 proved to be an excellent replacement for the classic Schmidt-Cassegrain. Its compactness, optical quality, precision focusing system, and focal length—1800 mm with an f/10 ratio—allow for a wide range of applications, from deep-sky observations to high-resolution observations.

 

Note: The Challenger 180 optics alone were available in 2003 at a price of 2000 euros, while with the M5 Plus mount equipped with Night Technology's Mechatronics two-axis motorization the price rose to 2750 euros.
The purchase price did not include a mirror diagonal, but I used the Intes Italia DX2 for 259 euros. Alternatively, at a convenient price, Diaframma supplied the two-inch Lumistar diagonal from Night Technology, which cost 125 euros.