Aligning two co-axial telescopes has always been a challenge. Scope rings require adjusting up to six individual screws to provide alignment. Then the slightest bump can knock the telescopes out of alignment.
The Libra Alt-Az mount was designed to make this alignment task simple and painless. Using a pair of clamps on one side to attach the female dovetail receiver to an existing male D-plate, the #19230 will fit directly on to any "D" style dovetail bar. A second pair of larger knobs on the opposite side provide both altitude and azimuth adjustments. A locking thumb nut secures the fine thread adjustment shaft for easy "no tools" installation and configuration.
- D-plate Width: 4.00"
- Overall Width with knobs: 5" to 8"
- Overall Height (level): 2.65" (2.3" to 3.0")
- Overall Length: 12.25"
- Clamp Width: 2.5"
- Altitude Adjustment: 4-degrees
- Azimuth Adjustment: 9-degrees
- Clamp Fasteners: 3/4" knurled aluminum
- Alt-Az Knobs: 1-1/2" knurled aluminum
- Knob Color Options: Silver
- Weight: 5 lb. 15 oz (2.7 kg)
- Payload Capacity: 25-lbs.
- Safety: Two 1/4"-20 knobs on male dovetail (NEW!)
- Optec Libra "D" series dovetail systems,
- Losmandy D series dovetail systems,
- Celestron dovetail bar,
- Farpoint D series dovetails systems,
- ADM "D" Series dovetail systems,
- Robin Casady's dovetail systems.
As an engineer once said, "The great thing about standards is that there are so many to choose from..."
As Dave Wagner pointed out in his excellent Cloudy Nights Review of the Libra Alt-Az, there are simply no real mechanical standards in astronomy. The "D" plate dovetail specification originally designed by Scott Losmandy is a wonderful example.
The "D" dovetail is generally accepted as a 4" flat plate machined with a 60-degree dovetail cutter to about 1/4" depth. Interestingly however, if you vary that depth just a bit we end with a widely varied dovetail profile. Male dovetails don't fit properly into female dovetails and you end with a less than ideal fit, or two pieces that will not fit at all.
For this reason we offer and propose the dovetail profile shown in the pdf at left. The key to measuring a dovetail properly is to use a standard MOW technique ("measure over wires" as defined in the Machinists Handbook).
This MOW specification uses a standard 3/16" ground dowel readily available through many suppliers. Slip two of these 0.1875" diameter dowels into opposite sides of the male dovetail and measure across with a micrometer or calipers. The ideal nominal MOW should be 3.200" +/- 0.020". That's about 1mm of variance allowed on the male dovetail.
We have measured dozens of male dovetail plates from the various manufacturers and found that most generally fall within this 1mm tolerance.