Re: [ATM] Focal Plane Location

[Richard <cnc@cncservo.co.uk>]

Hi Gilbert,

Monday, November 14, 2005, 3:54:12 PM, you wrote:

GG> 1. Where should the focal plane of the primary mirror be located
GG> relative to the mounting base of the focuser?

Such that all your eyepieces can be focused. You may want to
allow for a camera too. See below.

GG> 2. Eyepiece specs specify their focal length; what is the location of
GG> the focal plane relative to the field lens? How can this be measured?

I've seen it vary from 6mm above the mounting rim to 50mm below
the mounting rim. By 'mounting rim' I mean the part of the
eyepiece that bottoms out on the top of the focuser tube. Ie,
the measurements are relative to the top of the focuser tube
with the eyepiece fully inserted. Some manufacturers will give
that dimension and some will make a range of eyepieces where the
dimension is the same for all focal lengths. Confocal(?)

GG> 3. For star images to be "in focus", does the focal plane of the
GG> eyepiece have to be coincident with the focal plane of the
GG> primary mirror?

Yep.

-- 

Best regards,
  Richard in the UK

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