# Thread: 9mm illuminated reticle box size

1. ## 9mm illuminated reticle box size

Hi,

I have a Meade 9mm illuminated reticle guiding eyepiece and want to
calculate the guiding tolerances. Does anybody know the size of the
double crosshair box?

Thanks

Pere

2. ## 9mm illuminated reticle box size

Pere Sanz <peresanz@salbus.es> wrote in message news:<bl1hac\$g8sv74@news1s.iddeo.es>...

The size (in arcseconds) is a function of that eyepiece in your specific
brand/model scope. For example, in a scope whose focal length (FL) is 900mm
that eyepiece has a magnification of 100x and in a scope with a 2000mm FL the
magnification is 222x; the box's size in the FL(900mm) scope is more than twice
that in the FL(2000mm) scope in terms of arcseconds of sky. In other words more
"area" of sky is bracketed by the reticule box in the FL(900mm) scope than in
the FL(2000) scope.

What you want to do is find 2 stars each of which "sits" on one of the parallel
lines of the box and look up (or use a chart/planetarium program) the angular
separation of the two stars and that'll be the box's size in arcseconds for that
scope. Note you can rotate the eyepiece to facilitate positioning stars "on"
the reticule lines. Might be easier to do this with "common" doubles for which
the separations are well known; Albireo might be a good first target to get a
"handle" on this technique.

3. ## 9mm illuminated reticle box size

What does Meade say the size of the box is? That will determine, in
addition to the focal length of the scope of what the size of the box in
arcseconds.

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