Does a lens's rear opening size affect image quality on my Sony NEX-F3?
Asked 1/19/2013
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I have a Sony NEX-F3 with the 16mm lens and the 18-55mm lens. The 18-55mm seems to produce better-looking images. Does the larger rear opening on the 18-55mm mean it lets more light through and therefore uses the sensor better? Or could the 16mm be somehow not fully using the NEX-F3 sensor?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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No. Lenses are designed to cover a certain image circle which is larger than the camera's sensor. All lenses with the same or larger image circle use the full surface area of the sensor.
The amount of light that reaches the sensor is dictated by the aperture used to take the picture and the shutter-speed. More light results in a higher signal-to-noise ration and therefore less apparent image noise.
The size of the rear opening is dictated by the lens design and has nothing to do with the quality of images it produces. Ideally, the size should exactly match the projection of the sensor based on the angle of incidence of light falling on it.
Originally by user1620. Source · Licensed CC BY-SA 4.0
user1620
13y ago
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No. The size of the rear opening by itself does not determine image quality or whether the sensor is being “fully used.” Lenses made for the camera are designed to project an image circle that covers the whole sensor, so both lenses use the full sensor area.
How much light reaches the sensor is determined by the aperture setting and shutter speed, not simply by how large the rear opening looks. More light can improve signal-to-noise ratio and reduce visible noise, but that is about exposure settings and lens aperture, not rear element size alone.
The rear opening size is mainly a result of the optical design. A larger-looking opening does not automatically mean sharper images, better quality, or better sensor utilization.
If the 18-55mm looks better to you, the reason is more likely differences in lens design, focal length, aperture used, focus accuracy, or shooting conditions—not that the 16mm is failing to use the NEX-F3 sensor properly.
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