RE: ATM center dotting secondaries

["Bertapelle, Ken" <Bertapelle.Ken@tci.com>]

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.  I now believe that centering the 
secondary in the eyepiece can be most accurately done using a nonmagnifying
eyepiece with crosshairs, or a cheshire eyepiece.  That's the way I do it
now.  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.

- KenB

> -----Original Message-----
> From: gf [mailto:gforney@erols.com]
> Sent: Tuesday, July 27, 1999 6:00 AM
> To: atm
> Subject: ATM center dotting secondaries
> 
> 
> 
> I'm collimating my 8" dob newtonian.  One of the procedures I've come
> accross (from Kriege and Berry's book on building large 
> dob's) reccomeds
> center dotting the secondary.  I can see that this would be 
> very helpful
> in alligning the optics but would have thought that unlike center
> dotting the primary that doing this to the secondary would result in
> obstructing some of the image.  any thoughts?  If center 
> dotting is not
> a good idea how then do I ensure that the secondary is centered
> precisely under the focuser tube.  I don't need a whole treatise on
> collimating but just need to know whether I should get out the black
> magic marker tonight!
> thanks,
> glenn
> 
> gforney@erols.com
>