Re: ATM ronchi question

["AstroJack's Email!" <AstroJack@AVATM.com>]

Harold,

Also Take a look at this site.

http://www.phil.uu.nl/~gjv/atm/ronchishadows.html

You describe figure 1 for inside RoC and figure 6 for outside "RoC"

Mind you the over/under corrected is based on a sphere in these examples, so
a under corrected sphere would be a very undercorreced parabola.  Also an
over correceted Sphere is exactly what a parabola is.  At f/6.4 you do not
need a whole lot of correction.  What you want to have is figure 6 on the
inside of RoC and figure 1 on the outside of RoC.  Those are just ball park
and the curve of you lines my be less severe at (Less curved) at the longer
f ratio.

hope this helps!

Jack Day

p.s.  All the email I send to you off list is rejected by your postmaster.
What is your correct email address?

Thanks.



----- Original Message -----
From: "Harold" <adams@rmci.net>
To: "atm" <atm@shore.net>
Sent: Monday, January 28, 2002 7:30 PM
Subject: ATM ronchi question


>
> I have a 12.5" f/6.4  that i am trying to figure into a sphere. I have not
> previously  seen what a a sphere would look like in focault but have some
> idea what to look for but how should  a sphere appear in a ronchi test?  I
> used a 100 LPI . and at a slight distance inside of focus there are many
> straight lines, but when i move the grating closer to roc where only 2
lines
> show, they curve inwards.and at 2 lines outside roc they curve out. If i
> move closer to roc so that only one line shows then it buldges slightly in
> the  middle and narrows some towards the edges.
>
>   With the focault and no viewing scope it looks like the mirror darkens
> evenly at roc but  with a viewing scope there appears to be a slight
central
> depression . There is a difference of 30 thous. between edge null and
center
> null. Does this sound like im close to a sphere or not. After 23  15 min
> sessions TOT  1/3 coc stroke, i have only reduced the difference between
> center and edge null from 60thous. to 30 thous.  If more is needed then
may
> i need a different plan of attack.  Any suggestions.?
>
>   Hal
>
>
>