Why don’t DSLRs use a protective glass barrier behind the lens mount to keep dust off the sensor?
Asked 5/10/2012
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Interchangeable-lens cameras can get dust inside when lenses are changed, so it seems like a fixed glass panel behind the lens mount could protect the mirror box and sensor area. Since lenses already contain many glass elements, would adding one more in the camera body be practical? Do any cameras use this approach, and what are the trade-offs for image quality, cleaning, sealing, or camera operation?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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Sigma DSLRs have this feature instead of dust-reduction which almost all others have. In the case of these Sigma DSLR, this also block IR light from reaching the sensor while other DSLRs have a filter right in front of it to do that.
The suggestion of @rfusca is one I thought of before. It would probably not be complicated to have a protective cover in place which gets opened up when a lens is mounted. It would be hard to make such a moving part completely sealed, so the sensor clean function would need to open it too (in addition to lift me mirror).
Remember though that if your camera and lens are not both sealed, particles can still enter the camera. Leaving an optical grade class there could help but it would probably add unwanted internal reflections when bright light are in the scene.
Originally by user1620. Source · Licensed CC BY-SA 4.0
user1620
14y ago
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Generated from our catalog & community — verify before relying on it.
Some cameras have used a similar idea: certain Sigma DSLRs place a filter near the mount that also helps block IR. But in most DSLR designs, adding a fixed glass barrier is not ideal.
Main drawbacks:
- Image quality: Any extra optical surface can add reflections, flare, and slight degradation.
- Dust doesn’t disappear: If the body and lens aren’t fully sealed, dust can still enter elsewhere. A barrier would not make the camera dust-proof.
- Cleaning becomes more frequent: A glass surface near the mount is exposed whenever the lens is off, so it could collect dust and need regular cleaning.
- Dust can still show in photos: Dust on glass close to the sensor can still affect images.
- Cost/complexity: It adds another precision optical part and possibly more moving parts if designed to open or close.
Also, most DSLRs already have filter glass directly in front of the sensor, often combined with IR filtering and dust-reduction systems. In practice, manufacturers have generally preferred sensor-shake cleaning and normal sensor maintenance over adding another exposed optical barrier behind the lens mount.
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