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Summer Triangle Challenge

Astro-Tech AT 106 EDT Refractor


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A Review of the Astro-Tech AT106 EDT Refractor.


Aperture 106mm

Focal Length 690mm

Focal Ratio F6.5

Primary Lens TMB Triplet design with one element made from Extra high Dispersion Japanese

Ohara FPL-53 glass with a collimatable lens cell

Focus Mechanism Dual speed Crayford with calibration marks on the focus tube. The whole focus

assembly can be rotated through 360°

Weight 6Kg

Length Dew Shield retracted 615mm

Dew Shield extended 698mm

I was asked to review this instrument from an astro-photographer’s viewpoint so I must confess from the start that no eyepieces were used during the process of this review.

On delivery, I found the telescope beautifully presented and protected in an aluminium flight case with an accurately cut foam lining that held the instrument very securely indeed. The black high gloss optical tube had a very good deep finish and the overall appearance oozed quality. Even the dust cap was finely crafted from aluminium and slid onto the end of the retractable dew shield comfortably but firmly.

The matching 114mm diameter tube rings were nicely produced in aluminium with substantial satin finished knobs for clamping the rings around the tube. The base and top of each tube ring had five standard camera mount threads (1/4”) in each surface for attachment to various types of dovetail bar or for the attachment of a piggy back guide ‘scope.


Figure 1The view from the side with the dew shield retracted

On closer inspection, the multi-coating of the lens was clearly visible, indicated by the soft green hue and peering down the tube it was evident that good baffling had been incorporated into the design to aid contrast and there was even an internal baffle in the dew shield. The dew shield was retractable and could be locked in any position using a knurled thumb screw. The shield had an extension of 8.3 cm from fully retracted to fully extended. The movement of this was very smooth.


Figure 2 - The view from the front with the dew shield retracted

The 2” focus tube with a single clamp bolt operating a brass collar also came with a 1.25” eyepiece adapter. The 2” eyepiece adapter held my Starlight Xpress SXVF M25C camera confidently and even with the weight of this and a 2” extension tube, once focussed, the assembly remained in place throughout my imaging sessions and there was no tendency for the focus tube to slide outwards thus destroying the focus.

The 10 to 1 reduction Crayford focus mechanism was a joy to use especially as I am used to a single speed Crayford on my own telescope. Total travel of the focus tube was 8cm and a convenient index scale graduated clearly in mm was etched into the top of the focus tube for quick setting up at the beginning of each session. As expected, with no diagonal in place, there was insufficient outward travel for use with my CCD camera so I used a 2” extension tube and achieved focus with the tube racked out to 6.8mm. A nice touch for the astro –photographer was the rotating body of the focus mechanism which allowed for the easy framing of objects.


Figure 3The 10 to 1 reduction Crayford focus mechanism

Although I received the telescope for review on 5th January, 2009 it wasn’t until 23rd January that conditions were suitable for imaging from my location but it was worth the wait as the image of the Rosette Nebula (see figure 4) that resulted from my first light with the instrument proved it to be a very capable imaging telescope. This image indicated that there was excellent correction for chromatic aberration and a pretty flat field (see figure 5) using my 23.4mm x 15.6mm CCD sensor which gave a field of view of 1° 56’ X 1° 17’. Considering the size of the sensor, I was pleasantly surprised by the lack of vignetting in the image.


Figure 4 - The Rosette Nebula showing good star colours and fine detail


Figure 5The top right hand corner of the frame showing excellent flatness

In summary, I very much enjoyed my time with the Astro-Tech 106 and only wish that the sky conditions had been better to allow me to take more images with it. If you are considering the leap to a full triplet APO refractor for imaging purposes, this excellent instrument should definitely be on your short-list. I want one!

All images in this review by Steve Richards

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Sounds a fine scope Steve. The optics are clearly up to the mark as your fine image shows and the edge of field performance looks good, a little star elongation but no surprise there with the APS chip.

The inability to bring the CCD to focus without an extension is disappointing. Also is there any way to screw in a T thread adaptor rather than using push fit connections. My concern with the scope would be flexion with heavier CCDs using external filter wheels. Screw fittings would improve security and possibly reduce flexion.

Finally, do you know the price?!

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  • 1 year later...

Up to the hood width and no doubt the different front elements it has identical features etc to my Revelation 600/6 Ed scope. It can handle a 40D and battery grip on fine focus whist at the zenith :D

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