Re: ATM offset ? from Rien

["Anderson, Jay" <andeja@mail.va.gov>]

Steve Bell wrote:

"There has been a lot of discussion about collimating/offsetting
diagonals... Basically, my advice is to mechanically collimate first
so that no offset is present, then if you want the full offset,
implement
it by moving the diagonal towards the primary (horizontal component,
given that the OTA is horizontal) and then away from the focuser
(vertical component). How you do this varies tremendously."

I was thinking you could accomplish the vertical (away from focuser)
part
of the offset simply by placing spacers (metal washers) between the vane
and inside tube wall (on the two vanes closest to the focuser).  This
seems
simple enough till I try to calculate the thickness the spacers would
need to
be.  If you wanted to offset the secondary by 1/10" then the spacers
would
need to be somewhat less than 1/10" thick so you could start with 1/10"
spacers and file them (checking them with a micrometer).  Looks like it
is
hard to accurately measure just how much offset has been applied to the
secondary so it is probably best to mathematically compute this and then
create spacers of the required thickness and assemble.

Jay D. Anderson, KF4LLZ