Why does the sensor opening look chamfered in reflections?

Asked 11/16/2022

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2 answers

When looking into a camera body, the rectangular opening around the sensor sometimes appears to have a small chamfered corner in reflections. But the sensor/filter surface itself seems flat, so if it were acting like a mirror I would expect a perfect right-angle corner. What causes that chamfered appearance?

lens-mount reflections sensor optics camera-body

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

3y ago

2 Answers

It is a shadow of the lens mount due the lighting angle... this image makes it more apparent:

Also note that your blue line is incorrect and the sensor plane begins at (nearer) the red line... the black between those two lines is also shadow.

Originally by user70370. Source · Licensed CC BY-SA 4.0

user70370

3y ago

AI Answer

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It’s usually not the sensor surface itself being chamfered. The effect comes from the geometry and lighting around the sensor opening.

Two things are involved:

Shadow from the lens mount/opening: At certain viewing and lighting angles, parts of the mount or recess cast a shadow, which makes the corner look clipped or beveled.
A beveled/knife-edge mask around the image area: Cameras often use a machined edge around the sensor/filter opening to create a clean, sharp boundary to the recorded image. A chamfer can form that knife edge and reduce unwanted shading or soft edges.

So the apparent “chamfer” you see is typically the combination of the recessed opening, its beveled edge, and the way light falls on it—not the sensor acting like a perfect mirror with an actually cut-off corner.

Why does the sensor opening look chamfered in reflections?

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