SV: ATM center dotting secondaries

["Nils Olof Carlin" <nilsolof.carlin@telia.com>]

Ken and Glenn,

>I used the same book and followed the same advice when I built my 10" dob,
>and I've since concluded that it would have been better if I had not dotted 
>the secondary.  Not, however, for the reason you mentioned (obstruction of
>the image), but because of my limited ability to accurately place the dot
>in the *dead* center of the secondary. 

What center? ;-) The mechanical or optical one??
No kidding, if you center the *periphery* of the secondary using a suitably sized 
sighting tube in the focuser (as seen inside the inner opening of the sighting tube), the 
mirror center will be right on the virtual spot - offset and all! And no crosshairs. 

>And each time I do it I get a little jolt of annoyance with myself
>because the dot is always right there looking at me, and it's slightly
>off center!  Aaaarrrrrrghhhh.

The method above would neatly solve this dilemma, too ;-)

Nils Olof