What is the effect of a longer object-to-image distance (OID) on magnification?

What is the effect of a longer object-to-image distance (OID) on magnification?

• A. Magnification decreases
• B. Magnification remains unchanged
• C. Magnification is unaffected by OID
• D. Magnification increases

Answer: (D)

When the image plane sits farther from the object in a lens system, the image that forms on that plane grows in size. The image height scales with the image distance relative to the object, so for a fixed object height the projected image height increases as you increase the distance from the object to the image plane. Since magnification is the image size divided by the object size, increasing that separation boosts magnification. In other words, a longer object-to-image distance means a larger image on the screen or sensor, so the magnification goes up. (Keep in mind that you’ll usually need to adjust focus to keep the image sharp as you change distances.)

When the image plane sits farther from the object in a lens system, the image that forms on that plane grows in size. The image height scales with the image distance relative to the object, so for a fixed object height the projected image height increases as you increase the distance from the object to the image plane. Since magnification is the image size divided by the object size, increasing that separation boosts magnification. In other words, a longer object-to-image distance means a larger image on the screen or sensor, so the magnification goes up. (Keep in mind that you’ll usually need to adjust focus to keep the image sharp as you change distances.)