From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


Hi Ken
 The laser moving when racked in and out is an indication
of a bad focuser and has little to do with secondary/focuser alignment ( as
long as the secondary is flat. We are not talking about SCT's here ). Ross
is correct, other than mechanical issues( like problems with equatorial
mounts ), the focuser can be at quite large angles to the OTA and still
provide excellent viewing.
Dwight


>From: "Ken Hunter" 
>
>
>----- Original Message -----
>> The focuser need not be square to anything.  The
>> important thing is that it points directly at the
>> optical center of the secondary (that is, where the
>> optical axis hits the secondary, not its physical
>> center).
>
>THIS IS NOT TRUE!
>
>You can point the focuser at the exact center of the secondary
>(even if the focuser is mis-aligned at a 45 degree or other angle).
>If the light coming from the Primary is reflected at 90 degrees,
>you want the focuser pointed at the exact center of the secondary
>(neglecting the offset) AND... at a 90 degree angle.
>
>The proper test for focuser alignment is to use a laser or sight tube.
>If the laser dot or imaged crosshairs DO NOT MOVE when the
>focuser is fully racked in and out, and it is pointed to the proper
>place on the secondary, it is aligned properly.
>
>Ken Hunter
>
>
>
>
>

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