What is the formula for converting from one grid to another?

What is the formula for converting from one grid to another?

• A. mas1 / mas2 = gcf1 / gcf2
• B. gcf1 / gcf2 = mas2 / mas1
• C. mas1 + mas2 = gcf1 + gcf2
• D. new mas = old mas x (gcf2 / gcf1)

Answer: (D)

Changing grids requires adjusting the exposure meter setting (mA·s) so the image receptor still receives the same amount of exposure. The Grid Conversion Factor (GCF) tells you how much each grid changes the required exposure. To keep the receptor exposure constant when moving from one grid to another, the mA·s must be scaled by the ratio of the new grid’s GCF to the old grid’s GCF: new mA·s = old mA·s × (GCF_new / GCF_old). This comes from the fact that mAs1/mAs2 = GCF1/GCF2, which rearranges to mAs2 = mAs1 × (GCF2/GCF1). If the new grid has a higher GCF, you’ll need more exposure; if it has a lower GCF, less exposure is needed.

Changing grids requires adjusting the exposure meter setting (mA·s) so the image receptor still receives the same amount of exposure. The Grid Conversion Factor (GCF) tells you how much each grid changes the required exposure. To keep the receptor exposure constant when moving from one grid to another, the mA·s must be scaled by the ratio of the new grid’s GCF to the old grid’s GCF: new mA·s = old mA·s × (GCF_new / GCF_old). This comes from the fact that mAs1/mAs2 = GCF1/GCF2, which rearranges to mAs2 = mAs1 × (GCF2/GCF1). If the new grid has a higher GCF, you’ll need more exposure; if it has a lower GCF, less exposure is needed.