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Focal Reducers

Focal Reducer

CCD-FR distance (mm)

FR focal length (mm)

Focal ratio of scope


Calculated focal ratio

Calculated in-focus required*





a = Distance of CCD from focal reducer
b = Focal length of FR
c = Focal ratio of scope

The Meade/Celestron focal reducers have the following focal lengths.
[note: Around 2006 Meade manufactured some 0.63 focal reducers with a focal length of around half what they should be making them unsuitable for use with SLR cameras or filter wheels, any marked "Japan" are OK, as are later "China" ones.]

FR 0.33x focal length = 85mm
FR 0.63x focal length = 285mm

William Optics 0.8x FR focal length = 260mm

ATIK 0.5x FR focal length = 80mm

* Note that the in-focus figure assumes that the FR-CCD spacing is added to your physical imaging train length (as when using the Meade/Celestron FR's with spacing tubes). If you are using a FR like the ATIK that is fitted internally, then you have to add the FR-CCD spacing to this figure (to make it smaller). If you are using a FR like the Meade/Celestron then you will have to subtract the depth of the FR itself to this figure (to make it a larger negative number).

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This site was last updated 03/07/12