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I would imagine that all field flatners come focal reducer for refractors would be tailored for apochromatic refractors, not achromatic refractors. This being due to the chromatic aberration created by the objective being too uncontrolled compared to apo's.
In so far as just a focal reducer goes, again chromatic aberration would remain as too the field curvature, especially with fast refractors, and particularly when using a DSLR, if not even more pronounced.
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