The Astro-Physics Right-Angle Polar Alignment Scope (RAPAS) is a precision-machined instrument designed to simplify and improve polar alignment for astronomical mounts, eliminating neck strain often associated with traditional polar scopes.

Function Description:

The RAPAS allows users to align their equatorial mount by positioning Polaris (or Sigma Octans in the Southern Hemisphere) on its reticle according to an associated smartphone or computer application. This is achieved by adjusting the mount's altitude and azimuth knobs. The device is designed for high accuracy, with optics and reticle precisely centered and collimated from the factory, requiring no further adjustment. It's important to note that secondary alignment routines (like Polaris or 2-Star alignments) should not be performed after a RAPAS alignment, as this may decrease accuracy.

Important Technical Specifications:

Optical Tube: Features a 25 mm f/8 lens.
Eyepiece: Focusable with a reticle.
Illuminator: Adjustable brightness, powered by two pre-installed 1.5 volt GPA76 button-style alkaline batteries.
Machining Tolerances: Measured in 10,000ths of an inch, ensuring high precision.
Mount Compatibility:
- Mach1GTO (serial # M10670 and later), 1100GTO, 1600GTO: Designed to receive the RAPAS without modification. Users remove a cap and three placeholder screws, insert the scope, and secure it with three thumbscrews.
- 1200 Mounts (1200DA White, 1200QMD, 1200SMD, 1200GTO): Requires replacing the mount's threaded Polar Axis Rear Cap (M12660 or M12666) and Polar Alignment Scope Plug (M4037, if present) with the RAP1200 adapter. The adapter is attached using the original screws, ensuring the two RAPAS alignment holes are towards the top. The bearing thrust plate must not be turned during this process.
- 900 Mounts (900HDA, 900QMD, 900SMD, 900GTO): Requires removing the Polar Axis Rear Cap (M9403 or M12666) and Polar Alignment Scope Plug (M4037, if present). The existing rear plate remains in place and the RAP900 adapter is sandwiched between it and the axis, using new 10-32 x 5/8" screws. The single RAPAS alignment hole on the adapter must be towards the top. The bearing thrust plate must not be turned, and the existing rear plate's orientation must be maintained.
- Mach1GTO (serial # M10669 and earlier): Uses the RAPM1 adapter, which is a two-part adapter. The inner adapter screws onto the polar axis, with an etched line oriented vertically. Three tiny set screws lock it in place. The second part of the adapter is then secured, ensuring the RAPAS alignment hole is towards the top.

Usage Features:

Ease of Use: Once the RAPAS adapter is installed, the RAPAS itself is simply inserted and secured with three thumbscrews, ensuring the eyepiece is upright and registration pin(s) align with the adapter's hole(s).
Mount Leveling: For greatest accuracy, the mount should be leveled in the East-West direction. North-South leveling is less critical as altitude adjustments compensate.
Equipment Configuration: Highest precision is achieved when the RAPAS is used with the same equipment configuration each time, as changes can introduce flexures affecting alignment accuracy.
Push-Pull Adjustment System: While the RAPAS is highly accurate out of the box, a "push-pull" system allows for precise adjustments to the adapter plate's angle if needed. This involves loosening attachment screws and pushing with set screws to fine-tune the polar star's position on the reticle. This system allows for swapping the RAPAS between multiple Astro-Physics mounts with high precision, provided each adapter has been adjusted.
Drift Alignment (R.A. Correction Method): The manual describes a modified drift alignment procedure to minimize both Dec. and R.A. drift, particularly at the zenith. This involves zeroing out Dec. drift at the celestial equator/meridian using azimuth knobs, then zeroing out R.A. drift near the zenith using altitude adjustments. Guiding aggressiveness should be set to 0% during this process.
Standalone Use: The RAPAS can be used without a smart device or computer by calculating the Polaris Hour Angle (RAPAS Reticle) using Local Sidereal Time and Polaris R.A. (JNOW).
Focusing Procedure: The RAPAS is pre-focused but can be adjusted. First, focus the eyepiece until the reticle lines are sharp (best done in daylight). If stars are not sharp, loosen the knurled ring on the front optical tube and turn the tube to focus, then retighten.
Reticle Orientation: The reticle's North-South orientation is pre-aligned but can be readjusted. This involves leveling the mount, centering Polaris with the azimuth adjuster, slightly loosening the "Do Not Loosen Screw(s)" on the scope's back (and potentially front), rotating the assembly to orient the reticle so Polaris moves vertically when adjusting altitude, then re-tightening the screw(s).

Maintenance Features:

Adapter Permanence: The RAPAS adapter must always remain attached to the mount. Only the RAPAS itself is removed.
Battery Replacement: The illuminator uses two GPA76 button-style batteries. To replace, unscrew the two halves of the illuminator. Batteries are inserted into the narrow section with the negative (-) side towards the eyepiece and the positive (+) side towards the tapered On/Off switch.

ASTRO-PHYSICS RAPAS - Page 2