Telescope Review

Astrograph

Developed primarily with imaging in mind, the TS71SDQ delivers a 4.6° x 3.1° field of view on a full frame DSLR sensor and 3° x 2° on an APS-C crop sensor. Rich fields like these embrace the Andromeda galaxy, the Orion and Rosette nebulae as well as the Pleiades, plus many more popular celestial objects. The prime focus magnification is 10x. A DSLR can be attached easily with merely a single adapter (TS-Optics #M63i-M48a) and a standard Ø48mm T-ring (optional) requiring about 32mm focuser travel to pin-point. Unfortunately, this adapter does not thread 2" filters which is inconvenient for serious astrophotographers.

Alternatively, though the image circle would be slightly reduced, a common 2-inch extension tube with filter thread and a T-ring thread at its other end attached to the telescope-side 2-inch ring clamp can be used to connect a DSLR.

OPtional camera adapters and T-rings are available for dedicated CMOS cameras and DSLR brands. The minimum back focus is 115mm from the 2" connection and 125mm from the M63 thread.

Connection Diagram

Telescope

As-is, the telescope is equipped with 2" and 1.25" ring clamp adapters for star diagonals enabling visual observation at a usable magnification range of 10x to 200x with kudos to superb optical correction performance. Owing to the telescope's backfocus, an optional 1.25" or 2" star diagonal is required for visual work with eyepieces. Further extensions are naturally required when working with a barlow lens.

Optical Tube

With no plastic parts used in critical places, the OTA weighs 3.2kg including a 100mm dovetail and tube rings, which are 1/4" threaded for piggy-backing gear. Finely crafted and machined, the tube comes with a white paint, a black focuser, red decoration rings and gold-colored screws. It is certainly a matter of taste, but this instrument is a real beauty to look at and look through. The tube length is about 365mm with retracted dew shield, therefore conveniently portable. The tube comes with a standard shoe for an optional view finder or finder scope. The TS71SDQ is delivered as a bare-bone without any accessories and casing for which reason its price could be kept low for a quadruplet optical design employing top-notch lens glass. Just like any telescope on Earth, it won't however deliver Hubble images but with this little quadruplet you can certainly compete with Digital Sky Survey images.

The focal plane in particular of refractors with 2" focusers designed for 2" star diagonals lies way behind the focuser. Imaging with a long outward focuser travel to reach focus trades against stability and risk of optical axis tilt. Often, the focuser travel range is too short to achieve focus. An adapter with, say, 40mm optical path accepting a standard T-ring optimizes a photographic setup and mostly sports a filter thread. However, The lower the adapter part-count the more rigid is the imaging connection.

The objective lens holder unit can be unscrewed after removal of the Ø88mm ring at the objective entrance and full retraction of the dew shield. By loosening it, you will achieve two goals, 1. slightly changing the focal length and 2. a shaky optical axis. Better keep the lens unit firmly seated unless temporarily removing it for optical cleaning. Also, be sure not to loosen the focuser unit while only intending to rotate the camera.

Out-of-the-camera cropped, else unprocessed image, no filters. The moon shows no color fringes whatsoever. Resolution, sharpness and contrast compete with a Ø150mm F5 Newtonian.

Uncropped high pass filter processed image with a 1.25" 2x barlow giving a focal length of about 1450mm (F20). Given the 3.92µm pixel size of the DSLR, F20 is the maximum meaningful ratio.

Baader AstroSolar Film, high-pass processed. The dark center is about the size of Earth. Compare with SOHO's image of the same day. Out-of-the-camera single unprocessed frame.

Baader AstroSolar Film, UV/IR cut filter, high-pass processed. The resolution with merely 71mm aperture at FL=1450mm (F20) is quite amazing. Compare prime focus with 2x barlow projection.

The 'Pacman Nebula', NGC 281, in Cassiopeia.

TS71SDQ, Uranus-C (IMX585), Kenko Astro LPRII, 139 x 90 seconds each at gain 220.
Image FOV = 1.35° x 0.76°

The 'Rosette Nebula' NGC 2244 in Monoceros.

TS71SDQ, Nikon D5300 (modified), Kenko Astro LPRII, 85 x 120 seconds at ISO1600.
Image FOV = 2.89° x 1.63°

Running Man nebula, NGC 1977, in Orion.

TS71SDQ, Uranus-C (IMX585), IR-Cut filter, 55 x 60 seconds each at gain 200.
Image FOV = 1.36° x 0.76°

'Western Veil Nebula', NGC 6960, in Cygnus.

TS71SDQ, Nikon D5300 (modified), Kenko Astro LPRII, 60 x 120 seconds at ISO1600.
Image FOV = 2.89° x 1.63°

20mm inwards from focus. Exposure 2.5 seconds at ISO 1600.

20mm outwards from focus. Exposure 2.5 seconds at ISO 1600.

Single frame unprocessed taken with a Celestron AstroMaster 80AZS achromat (F5) and the TS71SDQ (F6.3). Both 10 sec at ISO1600 in prime focus. Note that Mizar is a visual binary.

Pros

• Sharp, crisp, beautiful contrast
• Excellent chromatic and coma correction
• Top-class lens glass, high permeability
• Diagonal - barlow - eyepiece reach focus.
• Both tube rings threaded for accessories
• Compact, rigid, portable, finely crafted OTA
• Slip-free, smooth focuser
• Painless dual-speed focusing with F6.3 ratio
• No need for an optional flattener
• All OTA components threaded, tool-less disassembly
• Eliminates desire for upgrading, well, not too soon.

Cons

• Small image shift when tightening the focuser lock screw
• Lens cap sits loosely

Summary

An entirely regret-free purchase as well as a most convincing choice for all levels of astrophotography skills, both optically and mechanically, plus high portability. Owing to its integrated field flattener, high-end lens glass and optical coating, this little quadruplet is a most favorable combination of expense and satisfaction, also for novice and on-budget astrophotographers who wish to, and certainly will, enjoy using this telescope for a long time. A most pleasant reason for being left out in the dark.

Eyepiece

Because it is rare to find an 2" eyepiece under 24mm focal length, the Explore Scientific 18mm with 82° field of view has been chosen for the TS71SDQ to provide 25x magnification. The waterproof eyepiece is composed of 7 elements arranged in 4 groups with EMD multilayer coating while argon-purged to protect against fungus and condensation on inward lens surfaces. Effectively placed internal flat black baffles entirely eliminate stray light for maximum possible contrast. Threaded for 2" filters, the eyepiece offers a wide field and an advertised eye relief of 13mm, but you need to get your eye closer than that to enjoy the specified field of view. The view through is contrast-rich and clear. Unfortunately, the outer edge of the view is dominated by an orange-tinted halo. No disaster and within acceptable norm for its FOV and price range. According to the manufacturer, its 82° and 100° series are designed with priority on field flatness for observation of dark DSOs.

 

The SVBONY 6mm focal length, 68° eyepiece with 13mm eye relief (under USD 40.00, respect!) has been tested with the TS71SDQ on the Moon, Jupiter and Saturn at 75x magnification with surprisingly clear images of all targets, even with a 2x barlow at 150x. The SVBONY eyepiece outrivals for instance Vixen's 6.3mm Plössl with the added pleasure of a wider field and longer eye relief which are preserved when using with a barlow.

The views of Saturn and the Lagoon Nebula through a Ø150mm Newtonian and a Ø71mm APO are a treat, as are Jupiter and the moon with an ND filter. Peripheral coma, if any, is negligible. The advertised eye relief of 13mm does seem to be shorter though.

Also laudable, the eyepiece can be disassembled for lens cleaning whenever need be. The first-light experience attested that 'low cost' eyepieces from China are not at all of low quality when they come from the right manufacturer. This eyepiece is an icebreaker hard to rival in its price domain.

 

Star Diagonal

A diagonal mirror does not only ease on your neck but also serves as an extension to get an eyepiece well into focus. For testing the TS71SDQ, the 2-inch Explore Scientific 90° diagonal with dielectric coating and 99% reflectivity was employed because it can take full advantage of the telescope's light gathering power. Comes with 1.25" adapter and is threaded for 2" filters.

Barlow

Depending on how it is sandwiched, a 2x barlow provides 1.6 to 3 times extended focal length and visual magnification (depending on the distance of the barlow lens to the camera sensor). The Kasai Trading 2x short barlow sports two fully multi-coated lenses and is mechanically designed with flexibility. When unscrewed, the lens portion provides a Ø48mm/0.75 male thread which accepts a Ø48mm T-ring or a 2" diagonal sleeve while the other side snaps into a 2-inch focuser or extension tube, such as the mechanical part of the barlow. Comes with native 1.25" adapter and is threaded for 2" filters. Optically not the best choice due to notable peripheral coma.

Sandwiching for Focus

Likewise, a DSLR with a mounted Ø48mm T-ring in place of the diagonal can be focused in this manner while increasing the system focal length to 750mm for 1.67x magnified imaging at a focal ratio of 10.6. So equipped it is possible to take magnificent photos of the moon and small deepsky objects with a DSLR employing an APS-C sensor which is fully illuminated, but please note that the so used barlow introduces edge coma. Unless expensive, a barlow lens is often the weakest light-freight car in an optical train.

Filters

Cell mounted filters for deepsky imgaging typically measure 2 inches in mechanical diameter with a metric thread of M48/0.75 while the clear aperture is typically 46mm. The high optical quality of the TS71SDQ eliminates need for enhancement filters, however, when not narrow-band imaging a Light Pollution Filter will help block artificial light for contrast enhancement and a darker background to allow less painful post-processing.

For general deepsky imaging, an UV/IR-Cut filter will help obtain sharper images because near-infrared wavelengths, invisible to the human eye but to the CMOS sensor, can wash out detail and contrast. Before you buy a filter, please confirm which kind of filter your camera has built-in. For instance, an IR-Cut window is used for the ZWO ASI178Mx and ASI120Mx-S, while all shelf DSLRs have a built-in IR-Cut filter placed over the sensor. Inbuild filters though may not be as good as filters specifically developed for astrophotography. DSLRs can be modified and fitted for deepsky imaging by removing the IR-Cut filter. Then external filters such as Quad-band, Dual-band and Narrow-band filters can be used for given imaging applications.

Objective Filters

For Imaging Applications

It is not advertised, but you can use Ø77mm camera lens filters, such as LPR or ND filters, or a SAFE solar filter, threaded directly over the objective lens of the TS71SDQ. Light pollution filters are for example offered by Kenko Tokina ('Starry-Night' or, even better, 'Astro LPRII' filters). Just unscrew the dew hood and unthread the imprinted stopper ring. Ø77mm filters can then be threaded in place of the stopper ring. The dew hood can then be reattached. You are welcome to copy that but at your own risk.

Twin Plate

For Optional Accessories

A twin plate serves more than a single purpose. It is not only a grip for more safely holding the telescope, but also provides two threads, 1/4" and 3/8" each, for mounting a finder, guidescope, a camera on a ball head, other photo gear, or a smartphone holder. The product, for example that of the Japanese manufacturer Etsumi, which is about 180mm long and 30mm wide, has a 2mm thick cork layer on one side which protects the surface to which is it attached with two 1/4" knob screws, such as the telescope's tube rings as shown on the photo.