For a FT 35 bifocal, the distance between the optical center and the edge used to calculate image jump is?

For a FT 35 bifocal, the distance between the optical center and the edge used to calculate image jump is?

• A. 4.5 mm
• B. 5 mm
• C. 3.5 mm
• D. 6 mm

Answer: (A)

Image jump depends on how far the near segment edge sits below the distance optical center in the lens. For a flat-top 35 bifocal (FT 35), the standard geometry places the edge of the near segment 4.5 mm below the distance-center line. This fixed offset is what’s used when calculating the likely image jump for that specific bifocal style. So, the distance from the optical center to the edge used in the calculation is 4.5 mm.

Image jump depends on how far the near segment edge sits below the distance optical center in the lens. For a flat-top 35 bifocal (FT 35), the standard geometry places the edge of the near segment 4.5 mm below the distance-center line. This fixed offset is what’s used when calculating the likely image jump for that specific bifocal style. So, the distance from the optical center to the edge used in the calculation is 4.5 mm.