You take an image with a 40" FFD (SID) with no tube tilt.  You then decide to take the same image with a 35 degree tilt.  What is the new FFD (SID)?

To calculate the new FFD (SID) with a 35 degree tilt, we can use the formula for the cosine of an angle in a right triangle, which is adjacent/hypotenuse. In this case, the original FFD (SID) is the hypotenuse, the angle is the tube tilt, and we're solving for the adjacent side, which is the new FFD (SID).

Here are the steps:

1. Convert the angle from degrees to radians, because the trigonometric functions in calculators use radians. To do this, multiply the degrees by π/180. So, 35 degrees is approximately 0.61 radians.

2. Calculate the cosine of the angle. The cosine of 0.61 radians is approximately 0.81.

3. Multiply the original FFD (SID) by the cosine of the angle to get the new FFD (SID). So, 40" * 0.81 is approximately 32.4".

So, the new FFD (SID) with a 35 degree tilt is approximately 32.4".