กล้องหักเห (Refractors)

Compatibility of GSO Crayford Focusers with Refractor Telescopes

Credit: Agena Astro, last updated 2018

To make sense of the cryptic abbreviations in the table, see the Key below the tables.

Table 1: Telescopes on which some of after-market focusers should fit

Key for Compatibility Tables Above

* - 'Focusing Issues' are as measured with a GSO single or standard dual speed focuser with a drawtube travel length of 80mm. If you are considering a GSO linear bearing focuser, then the drawtube is 30mm shorter.

Focuser
GSO86 - GSO Crayford Focuser with 86.4mm Adapter (Single or Dual Speed)
GSO96 - GSO Crayford Focuser with 96.6mm Adapter
GSO112 - GSO Crayford Focuser with 112.6mm Adapter

The William Optics Synta Focuser with 96mm Flange can be used instead of the GSO96 focuser listed above, but the 'Focusing Issues' column data may not apply.

Connection Configuration:
ASOT - Focuser bolts inside adapter; Adapter screws on outside the telescope tube
FBIC - Focuser bolts inside collar already on the telescope tube
FBIT - Focuser bolts directly to inside of telescope tube

Focusing Issues (For visual use with a diagonal; Extension tubes will be required in most cases for direct camera connections for imaging applications):
ETD - An extension tube is definitely required for additional back-focus travel (need at least a 2" extension on the Celestron C6R).
ETL - It is possible that you might need an extension tube for additional back-focus travel. However, we don't have enough data to state this conclusively.
ETM - Most customers did not need an extension tube, although it is still possible that you might need one.
NR - No extension tube required.

Comments:
C1 - OEM focuser can be hard to remove
C2 - 3 customers had tubes with ID = 96mm and could use the original screws. One customer reported an ID = 97.5mm and needed new screws
C3 - Holes don't line up perfectly, so screws are angled and don't go in all the way
C4 - Customers have reported different tube diameters for different year models
C7 - Customers have reported different tube diameters for different year models; One customer had no problems inserting the GSO Crayford. Another had to machine the flange down by about 1/16" to make it fit inside the AT1010 tube.
C8 - The original screws on this telescope are cheap sheet metal screws and need to be replaced by M4 screws
C9 - GSO96 connects to collar on tube; GSO112 can be connected directly to the tube without the collar