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What is the backfocus (distance in inches/cm) of the 20″ / 16″?

April 26, 2017CM distance inches

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What is the backfocus (distance in inches/cm) of the 20″ / 16″?

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This is the distance from the SCT thread adapter most rear surface to the nominal focal plane: 16″ = 4.9 inches. 20″ = 4.2 inches. Note that the thread adapter is 0.70 inches thick. If you were to remove the thread adapter, the new dimensions would be: 16″ = 5.6 inches. 20″ = 4.9 inches.