[ATM] Calculating Focuser Length and Travel

[mwarne at network2000-hi.com (Mike Warne)]

Hi Al,

Usually racked in means "all the way racked in" not just to the edge of the
tube.  .75 inch might not be enough travel to focus all your eyepieces.

Sometimes this means the focuser tube will extend into your tube for a
distance.  If it extends too far into your tube, it will block a small
amount of light entering your scope.  To avoid this you could mount the
focuser on a spacer made from a small block of wood shaped to match your
tube diameter.  You will need to add the height of the spacer into your
calculation for racked in height. (As if it is part of your focus itself).

For my 8 inch,  I had a 10 inch tube,  so I allowed my focuser to extend
'into' the tube for 1 inch.


Mike.

----- Original Message -----
 I  can't make sense of weather or not the focuser should be racked all the
> way in parallel to where the tube hole starts, which gives me a focuser
> length of 4.25".
>
> Therefore do I have a focuser of 4.25" with .75" of travel? Is this
correct?
>