Aperture: 90mm, 3.5 inches
Focal Length: 600mm, f/6.7
Weight: 3.7kg including tube rings and one extension tube
Telephone: 49 (0)89 1892870
We knew that the TS APO906 refractor was a little different from the norm as soon as we opened its substantial flight case – there was a ‘spare’ 50mm-long section of the optical tube in one compartment.
Closer examination of the rest of the telescope showed that the tube is modular, being comprised of a longer 240mm section and a shorter section of equal length to the spare one in the compartment.
Finished in Teleskop-Service’s attractive stippled white powder coating with black gloss trim, the telescope felt solidly built.
The tube is flocked and baffled to stop stray light from spoiling the contrast, as is the lockable and retractable dew shield.
The 2.5-inch rack and pinion focuser also had a solid feel to it.
The 10:1 reduction drive was very smooth in operation, although it did make a soft squeaking sound when moved using the normal speed knobs.
A 2-inch eyepiece holder with a 1.25-inch adaptor is attached to the focus tube through a 63mm thread, which can also be used to mount imaging equipment.
Both eyepiece holders use anti-marring compression collars, the 2-inch having three retaining bolts and the 1.25-inch just one.
The whole focuser rotates through 360° and the focus tube locks through a single bolt working against the pinion rod.
We mounted the TS APO906 on our Sky-Watcher AZ EQ6 GT mount in equatorial mode for our tests, with the long tube section and one 50mm extension in place.
We started our observing session with globular clusters, enjoying great views of M13, M92, M5, M3 and the relatively minuscule M53 using our own 5mm eyepiece.
Using the same eyepiece, we were able to split the Double Double, Epsilon Lyrae, into its four component stars in moments of good seeing, while the Ring Nebula, M57, looked stunning.
Turning to Saturn, we added a 28mm tuning ring to our 5mm eyepiece to convert it to a 3.2mm eyepiece giving 188x magnification.
Again, in moments of good seeing we had some memorable views, including cloud band detail.
Changing to our 17mm eyepiece, we were rewarded with high-contrast views of open cluster M44 and excellent glimpses of galaxies M51, M81 and M82.
Although the intra- and extra-focus Airy discs were not matched, showing classic undercorrection, no adverse chromatic aberration was visible through the eyepiece and star shapes remained good across at least 85 per cent of the field of view.
Switching to imaging, we installed the second 50mm tube extension and the TS Photoline 0.79x focal reducer, the latter loaned to us for the purposes of this review.
We then used our own Bahtinov mask and the freeware live view capture software EOS Camera Movie Record to focus our DSLR on the bright star Arcturus in Boötes.
For our imaging test, we returned to globular cluster M3, and recorded good illumination across the field of view and good star shapes right to the edges.
Chromatic aberration was well controlled, with no colour fringing on bright stars.
Racking the focuser in and out showed a tiny amount of image shift, but we were very impressed with its smooth action.
The focuser held our imaging rig solidly in place, proving the advantage of a well-made rack and pinion design over that of a Crayford focuser for imaging purposes.
There was no risk of slippage during an imaging run, even with the telescope pointing at the zenith.
The TS APO906 refractor is a very portable, versatile and well-built instrument, and we would recommend it for both observing and astrophotography.
We were not able to test the telescope with a binoviewer (an optical device that allows you to look through two matching eyepieces at the same time), but with a 1.25-inch diagonal and our standard 25mm Plössl eyepiece in place, the focus tube extension was 65mm.
With both extension tubes removed, this would give a minimum available back focus of 115mm, so it should be able to accommodate most models.
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This review appeared in the August 2013 issue of BBC Sky at Night Magazine