6" apo as your only scope?

"Jon Isaacs" wrote in message
...

Focuser height is measured by racking it all the way in (down), then
measure from the top edge of the focuser tube to the outside surface of
the main tube.

Actually one has to figure out where the focal plane is. One way to
estimate
this is to focus an eyepiece, measure the distance from the top of the
focuser
to the tube and then assume that the field stop is at the focal plane and
correct for that.

I use the program Newtwin to look at the vignetting etc in my Newts...

Jon,

If the timing is right, you can focus the image of the Moon on a piece of
fine ground glass, or even the right type of paper, that you lie across the
top of the drawtube. Those of us prone to math errors like these more
direct approaches g.

Clear skies, Alan

"starman" wrote in message
...

Focuser height is measured by racking it all the way in (down), then
measure from the top edge of the focuser tube to the outside surface of
the main tube.

Any idea what the implications are with a Paracorr in the focuser?

By measure, it adds 2" to the height. I understand the end purpose of the
Paracorr, but I've often wondered what effect it has on the illuminated
area.

Stephen Paul

Any idea what the implications are with a Paracorr in the focuser?

By measure, it adds 2" to the height. I understand the end purpose of the
Paracorr, but I've often wondered what effect it has on the illuminated
area.

Stephen Paul

The location of focal plane of the scope remains the same so my guess is that
it similar to an eyepiece, it has its own field stop or in this case maybe
"clear view or some such thing.

jon