Recently there has been a surge of interest in small astrographs with short focal lengths – and for good reason.
The term ‘astrograph’ indicates that these telescopes are designed with astrophotography in mind, and what these scopes lack in aperture, they more than make up for with the wonderfully wide vistas that they bring to your imaging sensor.
The Teleskop-Service (TS) 65mm Quadruplet Astrograph has a substantial tube for such a small scope and it’s nicely finished, with a white powdercoat surface and contrasting black tube rings.
The fine-geared, glossy black, 2-inch rack-and-pinion focuser is well engineered and comfortably held our photographic equipment with no slippage at all, even with the tube pointing up close to the zenith.
Usefully, the 64mm-long focuser’s drawtube was etched with a millimetre scale for recording the focus position for different eyepieces and cameras.
A finder shoe is attached to the focuser housing which, although described as Sky-Watcher compatible, was too tight to accept our older Sky-Watcher 9×50 finderscope, though it was fine with the latest version.
There is a retractable metal dew shield and a well-fitting aluminium dust cap.
The scope’s ‘quadruplet’ optics are arranged in two groups, with a front triplet lens backed up by a rear lens that acts as a field flattener.
The multicoated 65mm aperture, f/6.5 triplet lens has a focal length of just 420mm, giving a field of view of about 3° by 2° with the typical APS C-size sensor found in DSLRs.
To put this into perspective, the field of view would hold Orion’s ‘belt’ stars.
We were keen to explore the TS’s optical credentials and we weren’t disappointed.
The hallmark of a good refractor is a crisp, high-contrast view and we certainly got those in abundance.
Slewing over to the Pleiades star cluster we were rewarded with an excellent wide-field view of the whole cluster in our 25mm eyepiece, and stars to the edge of the field of view remained well formed.
This would make an excellent ‘grab and go’ telescope, and its size makes it very suitable for hand luggage.
But this telescope is being marketed as an astrograph, so we naturally wanted to put it through its astro-imaging paces – and again, it didn’t disappoint.
Our star test images on Vega, pictured right, were very impressive, showing excellent star shapes at the centre and right into the corners of our field of view, which was 3.2° wide by 2.1° deep using our Starlight Xpress M25C colour CCD camera.
We needed an extension tube to achieve focus, though, and this was where we came across a small hitch: our 50mm Revelation extension tube’s undercut was not compatible with the TS focuser’s compression ring and it worked loose far too easily.
This is not a fault with the scope per se, but it does serve to underline the need for a universal standard for compression ring and undercut placement.
In the end, our Orion nosepiece extension tube was able to save the day.
The rack-and-pinion focuser was smooth in action, if not quite as smooth as a Crayford design, and focus was easily achieved using the 10:1 fine focus knob.
We did notice that tightening up the focus lock caused some image shift, but at the same time, we were impressed with how solid the whole assembly became.
We took a total of 14 sub-frames of 500s duration each and compared versions calibrated both with and without flat-field frames to check for sensor illumination.
The images revealed an acceptable level of vignetting, apparent as darker corners and edges in the frame. Flat-field frames would easily remove this.
We were very impressed with this scope.
If Teleskop-Service can maintain a tight grip on quality control at such a competitive price, they are onto a winner with this astrograph.
Four lenses are better than two
Most telescopes of this type and at this price are of the ED doublet design, in which extra-low dispersion glass is used in an attempt to avoid chromatic aberration – the failure of the telescope to bring all colours of light to the same point of focus.
That design has proved very successful, but although such scopes are often described as apochromatic they are really only very well corrected achromatic lens designs – a true apochromat requires a triplet lens.
What both designs have in common is that they require a field flattener to avoid distorted stars at the edges of the field of view.
The 65mm Quadruplet neatly addresses both these issues by using a multicoated quadruplet lens system in two groups.
The front group comprises a traditional apochromatic triplet lens using an element of FPL53 glass for excellent colour correction, while the rear section has a single ED glass element lens for field flattening.
This combination works very well indeed, producing well-formed stars right to the edge of the field of view.
Tube rings and dovetail bar
The well-crafted tube rings include nylon inserts in the hinges and bolts to protect the finish and ensure smooth operation. The heavy-duty, Vixen-compatible dovetail bar has nicely machined slots for the mounting bolts.
The retractable dew shield is very effective at preventing dew from forming on the optics. A nice touch was the inclusion of a locking thumb screw to keep it extended when viewing at high angles.
Scopes of this type often come with Crayford-style focusers, which can slip under the weight of a camera and other accessories. However, the 10:1 two-speed rack-and-pinion focuser supplied with the TS remained firmly in place throughout our imaging sessions.
Machined from aluminium and finished internally with a matt black coating, the robust tube is a great platform for the optics and focuser. It has a hard-wearing and attractive textured finish.
Rotatable eyepiece holders
The telescope comes with both 2- and 1.25‑inch eyepiece holders, with compression fittings to avoid damage to the eyepiece barrels. For imaging use, the end of the focus tube can rotate through 360° to help you frame your shot.
- Price: £518.00
- Aperture: 65mm
- Focal Length: 420mm; f/6.5
- Weight: 2.8kg including tube rings
- Supplier: Teleskop-Service
- Telephone: +49 89 189 2870
- Website: www.teleskop-express.de