Starlight Instruments 3.5" Adapter Astro Physics Threaded Optical Tube Assemblies

The A35-503AP adapter is designed to connect a Starlight Instruments 3.5" Feather Touch focuser to an Astro-Physics telescope that has a compatible threaded rear cell. It ensures a secure, rigid, and perfectly aligned connection for both visual use and demanding astrophotography.

This adapter is specifically designed for the Starlight Instruments 3.5" Feather Touch focuser (FTF35xx series). It will not fit other sizes like the 2" or 3" models.

You must verify the thread specification on the rear of your Astro-Physics optical tube. This adapter is for specific "threaded Optical Tube Assemblies." It is crucial to consult your telescope's documentation or measure the rear cell thread to ensure it matches the A35-503AP before purchasing.

For astrophotography with heavy equipment, a threaded connection is superior because it prevents any possibility of sagging, tilting, or flexure as the telescope moves across the sky. This rigidity is critical for maintaining sharp stars across the entire frame during long exposures. A slip-fit or compression ring connection simply cannot provide the same level of structural integrity.

Installation is straightforward. First, you unthread and remove the stock focuser or rear cell adapter from your Astro-Physics telescope. Then, you carefully thread the A35-503AP adapter onto the exposed OTA threads until it is snug. Finally, you attach your 3.5" Feather Touch focuser to the adapter, typically using the focuser's own locking collar.

The rotational capability is a feature of the 3.5" Feather Touch focuser itself, not the adapter. The adapter provides a fixed, solid connection to the telescope tube. Once attached, you will use the focuser's built-in locking collar to rotate your entire imaging train to the desired orientation.