Re: ATM A few silly questions

[don clement <donald_clement@yahoo.com>]

A low profile focuser has a small distance from the
base of the focuser to the image plane. There is a
fixed distance from the secondary to the base of
focuser. When a focuser is "racked" all the way in
there is a minimum distance that must be added to the
distance from the secondary to the image plane. The
light from mirror to focus forms a cone. Adding
additional distance for focuser height means that the
secondary will have to be larger to accommodate the
focal plane pushed further from the focuser base.

There are two types of popular focusers that are used
today, the helical and the Crayford. The helical type
has a very low profile but suffers from lack of
travel. The Crayford sometimes is called low profile,
but in reality is not, due to a fixed tube length. A
version called a reverse Crayford puts some of the
tube and bearing support inside the telescope tube.
 
There is another type of focuser, not available yet,
that has very low profile of 1" and has long travel of
3". There is no drawtube and no part of the focuser is
inside the telescope or below the focuser base. This
is the focuser that I invented.

Don Clement
San Diego/Running Springs
The Clement focuser (patent pending)



--- Simon Fourstar <sfourstar@earthlink.net> wrote:
>  Also I want to build the focuser, I have a full
> tool shop to play in. I
> might as well use it. I am wondering what makes a
> low profile focuser, low
> profile? I have read about a few of the advantages,
> but haven't been able
> to find a clear definition of just what it is?


=====


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