What is the FFD usually set to?

• A. 1 metre
• B. 2 metres
• C. 0.5 metre
• D. 3 metres

Answer: (A)

Focus-to-film distance is the distance from the X-ray source (the focal spot) to the film. This distance determines how much the image will magnify and how sharp it will appear. A longer distance reduces magnification and improves sharpness, but you must increase the exposure to keep the film bright because the beam spreads out more with distance.

In routine veterinary radiography, around one metre is used as a standard setting. It provides a practical balance: magnification and distortion are kept low enough for a clear image, while exposure remains manageable for typical patient sizes and common detector or film setups. A shorter distance, like half a metre, would exaggerate magnification and blur detail; a much longer distance, like two or three metres, would require a much higher exposure to achieve a usable image and may be impractical with standard equipment.

So the usual FFD is set to about one metre.