**The focal plane distance depicted in the diagram is from the OA fold at the secondary to the focal plane inside the focuser. By default, the focal plane is placed at the midpoint of focuser drawtube travel. If this distance is already known in advance, it should be manually "keyed in" for more OTA dimensional accuracy.
Before "Printing" the scope diagram for your off-line reference, be sure and set your browser option to enable printing of "Background Images" - In IE5.0, it's in "Tools/Internet Options/Advanced/Printers/Print Background Colors and Images".
If an eyepiece "group" average fieldstop distance from the top of the drawtube is known, a more accurate F.P. Distance value for the eyepiece group can be determined for manual entry as follows:
- Enter all other parameters and "calculate" an F.P. Distance.
- Add 1/2 the total focuser travel distance to the "calculated" F.P. Distance value.
- Add the E.P."group" average fieldstop distance (a fieldstop located below the top of the drawtube is NEGATIVE distance)
- Manually key in this new value into the F.P. Distance field.