Televue NP 101 Review and Comparison

In recent years, dozens of short- and medium-focal length achromatic refractors from China, with apertures ranging from 80mm to 150mm, have become popular on the domestic and international markets. Sold under various brands, they share a low purchase price and practicality, but also modest performance, limited by mediocre optical workmanship and a lack of attention to detail that would otherwise lead to high production costs. While they have enjoyed considerable success among amateur astronomers, due to their affordability, they certainly cannot match the performance of apochromatic refractors. Moreover, not all amateur astronomers are satisfied with the performance of a mediocre instrument, and almost always decide to take the plunge toward the instrument that will be their ultimate instrument.

In this case, the choice is almost always difficult because it depends on various factors, such as the average seeing of the observing site, the preference for planetary or deep-sky observations, the available budget, and more. However, everyone has always wondered whether to prioritize aperture or contrast, whether to purchase a complex system, a mirror, or a high-performance apochromatic refractor. Who hasn't heard of their proverbial indifference to atmospheric turbulence, the sharpness of the images they display, and the perfect representation of colors?

In this review I will try to dispel some doubts that plague those who are undecided. The main question I asked myself was this: is it worth investing hundreds of euros in an apochromatic refractor?
To answer this doubt, I would dare say almost Hamlet-like, I tested one of the best ten-centimeter refractors on the market: the Televue NP 101, the brainchild of Al Nagler, a renowned American designer, renowned for his remarkable performance and the meticulous, thoughtful construction of his designs. It goes without saying that I will judge the instrument based on its focal ratio.

Model	Tele Vue NP 101
Opening	101 mm
Focal Length	540 mm
Focal ratio	F/5.4
Length	~650 mm
Weight	~4.5 Kg
Price (UnitronItalia – June 2021)	5299 VAT INCLUDED

 

FIRST IMPRESSIONS

 The instrument was delivered in a well-padded, hard-shell gray case equipped with a safety lock that has proven to withstand transport very well. The telescope is very compact, only about sixty centimeters long and weighing just under 5 kg. The optical tube is finished with white orange peel paint. The first thing you notice when looking at it is the presence of a sticker with the American motto "Proudly Made in America." The rack-and-pinion focusing system is excellent, better than that of Takahashi or Vixen refractors of the same diameter. Construction tolerances are truly minimal, so much so that if you try to force the diagonal into place, the pressure produced inside the tube will pop the cap that protects it. It also comes with a bronze locking ring for tightening the eyepieces and other accessories.

Both the interior of the focuser, with a 63 mm extraction, and that of the cell, are made of black anodized aluminum. The "starter kit" version supplied by UnitronItaly, Furthermore, it also includes a diagonal “everbrite”, two-inch collimable, allowing you to achieve focus with any eyepiece.

OBJECTIVE

The lens, well protected by a metal cover, is a quadruplet (Nagler-Petzval optical scheme) 101 mm with a focal ratio of F / 5.4. The Petzval optical design is formed by the union of a long focal length doublet with a field flattener/reducer placed near the focuser. In this way it is possible to correct most geometric errors (coma and astigmatism, first and foremost) as well as halving the focal length of the air-spaced doublet. Furthermore, the air-spaced doublet is composed of a Flint lens and a Crown, the positive element has been replaced with a so-called “low dispersion fluoro crown” which allows for excellent control of chromatic and spherical aberration. In fact, both daytime and planetary images are decidedly neutral and feature intense, true-to-life colors. The difference with the inexpensive ED doublet is clearly evident even at low magnifications. 

Image: The Televue NP101 apochromatic lens, in this case mounted on an old Vixen GP, which also proved to handle it without problems

STAR TEST

Furthermore, high-resolution stargazing could not exempt me from a star test. 
The result was exemplary: The Televue NP 101 showed no chromatic or spherical aberrations. The star diffraction images were perfect, even when observing very bright stars I did not notice any problems with chromatic residues, which are sometimes present even in apochromatic refractors. A quick comparison with the diffraction images provided by the Zeiss APQ 130 further convinced me: in the latter, in fact, there was a slight asymmetry in the extra focal length. Ultimately I can say that the Televue NP 101 surpassed almost perfect way the classic star test.     

PHOTOGRAPHIC USE       

This is obviously its favorite sector, thanks to the group of lenses near the focuser, vignetting up to 50 mm diagonal is very well contained. Furthermore, it is possible to use an optional field corrector to perfectly correct geometric aberrations. Thanks to the oversized focuser (3″ front aperture and 2.4″ rear aperture)  it was possible to eliminate any possible vignetting with large sensors but also increase the range compared to much cheaper solutions. Furthermore, during the possible rotation of the camera, it maintains, a perfect orthogonality with respect to the optical axis, thanks to the use of a translation tube equipped with three locking screws that fix on a threaded cone which also allows the use of various Televue photographic accessories.
The new focusing system is optimized with a 10:1 ratio reduction gear, allows for very precise focus adjustment and can be optimized with the optional micrometric kit. 

That Televue refractors were performing well in astronomical photography is also evident from these images obtained by Riccardo A. Ballerini, using a “vintage” Televue Genesis”

 
Image: M42 Nebula, courtesy of Riccardo A. Ballerini

 

FIELD PERFORMANCE IN VISUAL USE

 I believe many readers will skip the introductory part of the article to immediately check out this instrument's performance for observing solar system objects, even though it's a telescope with a focal length more suited to photography. Typically, the views a good refractor can provide aren't enough to justify using a larger-diameter instrument.

To test this assertion in the field, I compared it over several evenings with other instruments, thus highlighting its strengths as well as its limitations. The instruments in the comparison were: a 150 mm Newton Intes Maksutov (F/6), a 203 mm Celestron C8 (F/10), and one of the best apochromatic refractors ever built: the Zeiss APQ 130/1000. I realize it's not very useful to compare such different designs, but this is one of the most requested practical tests by amateur astronomers.

During the month of June, although Jupiter's visibility was not the best, the Televue consistently provided well-contrast images, even when the Schmidt-Cassegrain revealed a blurry, indefinite disk. On evenings with decent seeing, however, the images provided by the German refractor and the Russian Maksutov slightly surpassed those of the Televue in detail, although the differences were not that significant. The clear separation of the Galilean satellites from the planet's atmosphere during their various transits, the relative projection of their shadows, and the countless details present in the temperate bands were notable. Even the light scattering when observing such a bright object was very limited. I must admit that despite being a short-focal length refractor, it performs admirably even against more closed optical systems suited to lunar and planetary observations.

Looking through the Televue eyepiece and then at the 20-centimeter Schmidt-Cassegrain, the first impression is that I'm no longer able to focus with the catadioptric. The contrast and perfect focus (in proportion to its focal ratio) of the American refractor are so precise even on the most turbulent evenings that they generate this strange sensation. I wouldn't have expected such a clear snap test from an F/5.4.

Having to make a simple statistic, I could say that, having used the Televue NP 101 for fifty days, the average monthly usage was more than double compared to the Celestron C8. Due to the reduced focal length (540mm) and not being able to use a Televue focal multiplier, I opted for the Baader Planetarium Fluorite Super Barlow, which literally made lunar details explode when the seeing conditions allowed. This refractor can easily handle 300x magnification and beyond, without losing definition, while obviously making some concessions in brightness. It is in this type of observation that the clear superiority of a short-focal-length apochromatic refractor is highlighted over a cheaper achromatic refractor, which, with the same diameter, does not allow for such magnifications.

Observing Petavius crater with a 10 mm Televue Plossl eyepiece and the aforementioned FFC system, I admired the subtle deformities of the Petavius rim and the internal micro-crater. The contrast was excellent, as was the three-dimensionality of the image; the lunar disk stood out clearly against a dark sky, and it provided a faithful representation of the lunar albedo. 
The subdivision of the Rupes Cauchy and some of the microcraters that dot it are also clearly visible. I was unable to perceive the Fracastorius rift, but I could admire, albeit with difficulty, a portion of the rift within the Alpis Valles, a detail that many consider impossible for an instrument of this diameter. The favorable lighting conditions and excellent seeing revealed the faint structure within the Alpine region. For the record and to reiterate how essential lighting conditions are, Raffaello Lena, years ago on the same evening, was also able to observe the rift through his excellent Polarex Unitron 132 C Folded refractor, unfortunately no longer in production.

If I had to summarize the comparison with the other three instruments, I could say this: the Schmidt-Cassegrain proved superior in perceiving lunar details only on four out of fifty evenings. In those rare cases, it always revealed greater detail, but it challenged the observer's visual acuity. In fact, the image provided by a ten-centimeter apochromatic refractor is far more relaxing; in fact, I never encountered an evening where micro-turbulence wasn't noticeable inside the Celestron eyepiece.

For the Zeiss APQ 130, things were different. Due to its moderate diameter and considerable size, the German refractor was quite sensitive to turbulence, so much so that on evenings with average seeing it could not go beyond the performance provided by the Televue. On calmer nights, however, it was possible to easily utilize the 400x magnification, and in this case the images were among the most detailed ever seen from a "five-inch":

The 150mm Maksutov Netwon Intes (not the Deluxe version) was halfway between the Zeiss and the Televue. I was particularly pleased with the excellent configuration of the Russian optics, as well as the favorable price, even though it suffered more from focal turbulence than the Televue NP101.

Using the Televue NP101 with a 31 mm eyepiece of the same name, you can cover a full 4.5 degrees of field. For this reason, anyone who initially criticizes the lack of a finder scope in the standard equipment will have to think again, even if aiming at celestial objects without this valuable aid may prove difficult the first few times.
 Deep-sky observation, especially that of star clusters, is very rewarding, understandably within the limits of the aperture. It's undeniable that if you wanted to perceive the details of galaxies, you have only two options: choose a good observing site at least 2,000 meters above sea level, or invest in reflecting telescopes of at least twenty-five or thirty centimeters.

In fact, the star cluster M13, although beautiful and immersed in a wide, correct field with pinpoint stars, was better resolved in the twenty-centimeter Celestron. I can confirm that the image displayed by the NP 101 was quantitatively less rich in information but qualitatively more appreciable and fascinating, as only a high-quality refractor can provide. 

The observation of double stars was excellent, surprisingly the pinpoint sharpness even surpassed that of the Zeiss APQ 130 and I was able to perceive, through the analysis of the diffraction disk, even star systems well below the resolution limit of the telescope.

Even at low magnifications, I could easily admire the Airy disk of each star, which appeared as a faint but visible disk without halos.

PROS AND CONS

MERITS 

•  Excellent optical design for photography, but also capable of providing good performance in lunar and planetary observation
•  Mechanical quality
•  Finishing touches
•  Excellent containment of chromatic and geometric aberrations
• Little focal turbulence even if it is not a simple doublet
  
  DEFECTS
  
• Lack of supplied finder
• High purchase prices

IN SUMMARY

The time has finally come to answer the initial question. Is it worth investing money in an apochromatic refractor?
If quality is the first factor we demand from a telescope, the answer is undoubtedly: yes!

The Televue NP 101 has proven to be a high-quality all-rounder, excellent for astrophotography but also capable (with the right accessories) of observing the moon, planets, and open clusters. I also found it to be fairly insensitive to turbulence, thanks in part to the careful design of the optical scheme and tube. It is currently available for €5,299, including a case.

Thank you UnitronItaly dealer of Televue products, Federico Caro and Paride Berti, owners respectively of the 130mm Zeiss APQ refractor and the 150mm Intes Newton Maksutov, for kindly offering the comparison and Christina Irakleous  and Jeremy Horst for the images provided.

 

DISCLAIMER

Binomania is not a store. On my website, you'll only find reviews of sports, photography, and astronomy optical products. My opinions are impartial, as is the duty of any journalist, and I do not earn a percentage of any sales. Therefore, if you'd like to purchase any product or receive information on price changes or new products, I recommend visiting the official UnitronItalia website by clicking on the banner, which is the only form of advertising featured in this article. Thank you!