RE: ATM star test of 6"er

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

All,

Someone was showing me how to use the star test to collimate recently,
and he said that there is *always* a difference in the crispness of the 
diffraction rings on the two opposite sides of focus.  The explanation
was that on one side of focus the telescope is focused "beyond infinity"
into deep space, and on the other side it's focused "inside infinity"
such that it is catching much more of the turbulence in the atmosphere.
The diffraction rings are always much more shaky in this second case.

Since then, I've been able to see this difference each time I collimate.
But I haven't taken the care to notice whether the sharper image is
always inside focus.  What do you all think of this explanation?   

- KenB

> -----Original Message-----
> From: JoAnn Nanof [mailto:jnanof@javanet.com]
> Sent: Wednesday, July 21, 1999 11:58 AM
> To: atm@shore.net
> Subject: ATM star test of 6"er
> 
> <snip>
>
> I did the star test on vega. At about 100X (16X/in) I saw no 
> difference
> in the inside and outside of focus as far as the diffraction 
> rings were
> concerned. The rings were sharp and easily defined inside focus but
> there was a small difference in the sharpness outside focus. I think
> there may be a bit of a raised ring before the tde. At 190X (31x/in) I
> had the same results. 
>
> <snip>
> 
> Searching for Parabola,
> JoAnn.
> Portland, Me.
> Adventures of ATM Woman!
> http://members.tripod.com/nanof/atmwoman.htm
>