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Astro Digiscoping

The other way to the stars

The universe of digiscoping continues to grow, with the combination of spotting scopes and cameras also attracting the interest of amateur astronomers. German scientist Dr. Carolin Liefke, a renowned expert on optical devices in the field of astronomy, has, for this reason, used extensively the features offered by ATX/STX spotting scopes and digiscoping in general in her astronomical research.

© Dr. Carolin Liefke

Dr. Carolin Liefke is a research fellow in the Center for Astronomy at Heidelberg University. Apart from giving (popular) scientific lectures to various target groups, she is also an expert on optical devices used for astronomy. She used an ATX 30-70x95 spotting scope with a TLS APO adapter from SWAROVSKI OPTIK for her feature.

Spotting scopes have not yet been able to become established as compact refracting telescopes in amateur astronomy. One of the main reasons for this might be the skeptical attitude about the display quality of the reversing prism, which is not required at all during astronomical observations. However, the equipment in the SWAROVSKI OPTIK ATX/STX series should impress in this respect.

Even suitable for faint heavenly bodies

Discerning amateur astronomers find the largest models of particular interest – ATX and STX 30-70x95. Thanks to the impressive 95 mm lens diameter, they almost get close to the aperture of a conventional 4” refractor lens, thus enabling even faint heavenly bodies to be shown and details displayed at a resolution of up to 1.5”.

The bayonet connector allows either the straight STX eyepiece module or the ATX module at a 48° angle to be connected in a few easy steps.

Otherwise, the objective lens unit for both models is identical. In both cases, it is used as a zoom and covers a magnification range of 30x to 70x. The exit pupils are between 1.4 and 3.2 mm. Higher values would be desirable for smaller magnifications.

Ideal for use in winter

There is a ring on the eyepiece module for smoothly adjusting the magnification while you focus it with the objective lens unit. Both adjusting rings are generously sized with rough grooves so that they can also be adjusted when wearing gloves.

The eyepiece units operate with the same focal length, therefore the field of view must change in line with the magnification. With a field of view between 57° and 71°, spotting scopes are no longer viewed as simple eyepieces with a “tunnel vision” range, but they cannot reach the ultra-wide angle range that is currently used in astronomical eyepieces and is capable of supporting apparent fields of vision of up to 120°. However, the eyepiece modules have large lenses on the eye side and a comfortable eye relief of 20 mm/0.8 in, thus making them suitable for eyeglass wearers.

Although the display quality provided by both eyepiece modules is near enough identical, stargazers mainly opt for the ATX module with the angled view because of the more comfortable viewing position.

Coatings of the highest quality

Even when observing during the day, the exceptionally high contrast provided by the optics is striking. It is quite obvious from this how SWAROVSKI OPTIK has attached great importance to the quality of the coating of the optical interfaces, with the aim of successfully suppressing scattered light and maintaining high transmission. In a similar way to the EL series of binoculars, focus, color, and contrast settings go hand in hand. First of all, any slight residual color fringes next to objects with bright/dark contrast are reduced considerably or disappear almost altogether, accompanied by a noticeable improvement in the contrast as soon as the focus is set perfectly. The color purity of the ATX/STX 30-70x95 models can also be compared to an ED apochromat with the same aperture, even at higher magnifications, something that cannot be taken for granted, given the additional optical elements featuring in the optical path.

Stars like sparkling gems

In a starry sky, the exceptional display of the spotting scope is plain to see in perfect clarity. No matter which magnification is set, the stars are displayed as perfect dots without any colored coronas, right to the very edge of the field of view. In the case of bright objects such as planets, there are no reflections produced either that could interfere with the image.

As a result, the ATX and STX 30-70x95 can fully leverage their strengths as wide-field devices. Observing star clusters is a real pleasure, as it is reminiscent of sparkling gems on black velvet. A whole series of galaxies can also be observed thanks to the large aperture. The ideal magnification can be selected individually for every object.

  • © Dr. Carolin Liefke
  • © Dr. Carolin Liefke
  • © Dr. Carolin Liefke
  • © Dr. Carolin Liefke

Observing the sun is possible with a filter

It is also possible to observe the sun exceptionally well using a suitable lens protection filter (e.g. AstroSolar ND 5 from Baader Planetarium). Neither eyepiece module allows any detailed observations to be made at high magnifications, but the relative number of sunspots can be determined effortlessly. The granulation of the sun’s surface can also be clearly seen.

Compact and lightweight

The ATX and STX 30-70x95 models feature among the spotting scopes with a comparably large aperture, thanks to their 95 mm lens diameter. Devices with an aperture of more than 100 mm are hard to find on the market. One of the reasons for this is that such optics are getting heavier and their pack size is increasing, making them increasingly less portable. With a weight of just slightly more than 2 kg/75 oz and a length of 45 cm/17.7 in, the ATX/STX 30-70x95 spotting scopes definitely still feature among compact and comparably light models that can be stored in a suitcase or backpack, thus making them the ideal mobile travel device.

Rugged and multifunctional

The spotting scopes can also outmatch conventional telescopes in terms of their ruggedness. The noticeable features of the ATX and STX models include not only exceptional workmanship and the use of top-quality materials, but also a “rounded” design. The upshot of this, in turn, is that there are no protruding parts that could, for instance, sustain damage in transit. Similar to many binoculars, the ATX and STX 30-70x95 models are also watertight and filled with nitrogen.

Solid base for every observation

Just as with a conventional telescope, it is vital that the device is set up on a solid base. It is not practical to observe without using some kind of support. A stable tripod and good tilting head are the minimum requirements. As an alternative to directly attaching the device, SWAROVSKI OPTIK offers an easily adjustable rail as an accessory with the SSR II, which can be used to set the equilibrium of the optics in a flexible manner.

For anyone wishing to fit the spotting scope on an equatorial mount for astronomical applications, a prism rail can be effortlessly attached using a photo thread screw, making the device adaptable. An equatorial mount will enable them to track the earth’s rotation either manually or mechanically or, if necessary, to use a GoTo function. In terms of bearing the load, an EQ3 mount (e.g. Skywatcher EQ3-2, NEQ3, or others with the same structure) or higher is recommended.

Digiscoping for stargazers

An additional accessory available with the TLS APO is an adapter with an integrated lens optical system, which can be used to connect system and SLR cameras via a universal T2 adapter. The projection optics produces, depending on the zoom factor, focal lengths of between 900 and 2100 mm. This configuration is rather unsuitable for time exposures of deep-sky objects. However, the moon and sun can be displayed very well in their full format.