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Despite the Fx frame diagonal being 43.2mm, with a fast APO it is possible to accommodate the image circle,
unvignetted, with a two piece adaptor.
For example: TEC140APO f/7 prime focus & WO Sony alpha T-mount & 2-inch sleeve
The above diagram demonstrates that the WO adaptor's I.D. is just sufficient to fill the Fx frame at prime focus at f/7.
This however is not the case at slower f/ratios, and when a Barlow is employed. For instance a x2 Barlow decreases
the convergence angle to ~2º & contracts the unvignetted image circle to ~38mm.
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