Hi Leon
I just downloaded the FSQ-106 manual from Texas Nautical and it describes visual use with a 1 ¼ inch diagonal (Page 11) and a 2 inch diagonal (Page 12).
My reading of this is as follows:
1 ¼ inch diagonals
The FSQ-106 appears to have a compression ring focuser into which a 1 ¼ inch diagonal can be fitted.
A 1 ¼ inch diagonal has a relatively short light path through it, so it appears that it can be used with an eyepiece and you should get focus.
2 inch diagonals
A 2 inch diagonal has a much longer light path through it, so it appears it cannot be used visually unless you have the following optical train as described in the FSQ-106 Extender System Chart on Page 12:
- Multi-Adapter Ring (8)
- Visual Adapter (10)
- Extender-Q (60)
- Adapter-Q (66)
- Diagonal Mirror (74)
- 2 inch eyepiece (48)
I don’t why Takahashi have all these fiddly bits and pieces – it makes life difficult compared to the ubiquitous SCT accessory systems.
WARNING:
The manual also indicates that there is an optical element very close to the focuser compression ring – so be very careful about inserting eyepieces or diagonals with a long 1 ¼ inch sleeve, otherwise the end of the sleeve may hit the glass – ouch!
Cheers
Dennis