What is the primary purpose of the Starlight Instruments 3.5" End Cap for William Optics accessories?
This end cap is designed to adapt a Starlight Instruments 3.5" Feather Touch focuser to accept William Optics accessories, such as field flatteners or focal reducers, that use a male M92x1mm thread. It provides a secure, rigid connection for astrophotography.
Which Starlight Instruments focusers is this 3.5" End Cap compatible with?
This end cap is compatible with Starlight Instruments 3.5" Feather Touch (FTF35xx series) focusers. It is not designed for their 2", 2.5", or 3" models.
Why should I use this threaded 3.5" End Cap instead of a standard 2" compression ring adapter?
A threaded connection is significantly more rigid than a compression ring. For astrophotography with heavy cameras, filter wheels, or off-axis guiders, this end cap prevents flexure, tilt, and sag in the imaging train, which can ruin long exposures. A compression ring can allow for slight movement, whereas a threaded connection locks components together as a single unit.
How does the Starlight Instruments 3.5" End Cap improve my imaging setup with a William Optics flattener on my refractor?
By creating a solid, threaded connection between your 3.5" Feather Touch focuser and the William Optics flattener, this end cap ensures the precise backfocus distance is maintained without any tilt. This is critical for achieving sharp stars across the entire field of view, as even minuscule tilt in a flattener can cause distorted stars in the corners of your image.
Is the M92x1mm thread a common standard for William Optics accessories?
Yes, the M92x1mm thread is a common standard used by William Optics for connecting their larger field flatteners and reducers to focusers. However, it is always best to verify the specific thread size on your accessory before purchasing this end cap to ensure compatibility.
I'm building an imaging train with a heavy cooled camera and filter wheel. Will the Starlight Instruments 3.5" End Cap prevent sag?
Absolutely. This is exactly the scenario where this end cap excels. The robust, single-piece aluminum construction and secure M92x1mm threads are designed to support heavy loads without any flex or sag, maintaining perfect optical alignment even when your telescope is pointed near the zenith.
