Myopia Corrected: How the Diverging Lens Actually Works

1 · Predict

A myopic eye's diverging corrective lens (f = −70 cm here) is meant to make distant objects appear to be at the eye's far point instead. Does this work the same way no matter how far away the actual object really is?

• Within the object distances this bench can actually reach, the virtual image distance still varies a lot as the true object distance changes — it hasn't yet settled near the far point.
• Yes — for any sufficiently distant object, the diverging lens forms a virtual image very close to its own focal point (near the far point), regardless of the exact true distance.
• The corrective lens doesn't change the effective image distance at all.

2 · Set Up

1. Open the myopia-corrected preset and press Reset. The corrective diverging lens has f = −70 cm, matching this eye's far point.
2. Enable the corrective lens's image-distance readout.
3. Set the true object distance for each trial (all reasonably far) and record the virtual image distance formed by the corrective lens.

3 · Collect Data

Plot image distance d_i (y-axis) against object distance d_o (x-axis) for your three trials. Is d_i bending toward the lens's focal length (−70 cm, the eye's far point)? How close does it get over the range the bench allows?

4 · Analyze

1. For one trial, compute d_i from 1/f = 1/d_o + 1/d_i using f = −70 cm. Compare to the table.
2. Your table shows d_i still changing substantially even at the largest object distance this bench can reach (d_o = 100 cm, d_i only 58.8% of the way to f = −70 cm). Using 1/f = 1/d_o + 1/d_i, explain why d_i needs d_o in the many hundreds of cm before it gets truly close to f — this correction genuinely only becomes near-perfect for objects much farther away than this bench can place them, not for every 'distant' object.

5 · Extend

1. This is the actual mechanism behind corrective lenses: they don't change what the eye's own lens does — they pre-process the light so the eye 'sees' the corrected image at a distance it CAN already focus on. Explain why this means corrective lenses work WITH the eye's own optics rather than replacing them.
2. Compare this experiment's fixed f = −70 cm to the myopia experiment's corrective-power calculation for far point = 70 cm (P = −100/70 ≈ −1.43 D, so f = 1/P ≈ −70 cm). Confirm these are the same lens, described two different ways (focal length vs. diopters).

The Physics Behind This Experiment

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