[Brightcolours]

Valid points, especially the two filters. I imagine a half darkened stripe of optical glass to be moved from left to right. Adding not only one, but two moving surfaces (dust and wear, particles, oil...) in a very small volume of a camera body. Making it close to impossible to focus because of 10 stops amplification (or less, Fujifilm's ND filter coming with the 56/1.2 APD is ND8, so only 3 stops).

 

Sigma DSLR? Or the mirrorless sd quattro types? Anyway, most mirrorless cameras do have a glass element in front of the sensor. 

See Lensrentals Blog:

 

 

All digital cameras have glass in front of the sensor, JoJu.

[JJ_SO]

But not many shortly after the flange, BC.

 

And also not many have a glass element a couple of mm thick.

[Brightcolours]

(similar to high-end tele lenses, that allow drop-in filters and need to have a clean filter in there).

 

My Tamron SP 500mm f8 has small screw in filters, and  clear filter. How high end  :lol:

[mst]

My Tamron SP 500mm f8 has small screw in filters, and  clear filter. How high end  :lol:

It's actually a feature I wish more lenses offered. Nikon once had it in the AF-D 300/4.

[thxbb12]

Anyway, most mirrorless cameras do have a glass element in front of the sensor. 

See Lensrentals Blog:

           The Glass in the Path: Sensor Stacks and Adapted Lenses        

           Sensor Stack Thickness: When Does It Matter?        

           Sensor Stack Thickness Part III: The Summary        

           A Thinner Sensor Stack        

 

All sensors have glass in front of them, I'm aware of that.

That's not what I'm talking about.

I'm talking about a mechanism that would automatically protect the sensor itself so it would not be exposed when changing lenses.

It would prevent (or at least help prevent) dust from coming in and reaching the sensor.

Dust is obviously becoming more and more critical with high resolution sensors and keeping sensors clean of dust is not easy to achieve when often changing lenses in outdoor environments with potentially not clement weather.

[thxbb12]

It's actually a feature I wish more lenses offered. Nikon once had it in the AF-D 300/4.

 

That's what I'm talking about, but in the camera body rather than in the lens.

[mst]

That's what I'm talking about, but in the camera body rather than in the lens.

For ND, yes. However, when using polarizers, in-lens is probably less of a hassle

[thxbb12]

For ND, yes. However, when using polarizers, in-lens is probably less of a hassle

 

Yes, I was talking about ND filters ;-)

[toni-a]

Wonder why rear gel filters aren't that popular and only a few lenses take rear gel filters, a rear ND gel filter would fit any lens that takes gel filters, you course gel filters have limited durability but still

[JJ_SO]

All sensors have glass in front of them, I'm aware of that.

That's not what I'm talking about.

I'm talking about a mechanism that would automatically protect the sensor itself so it would not be exposed when changing lenses.

It would prevent (or at least help prevent) dust from coming in and reaching the sensor.

Dust is obviously becoming more and more critical with high resolution sensors and keeping sensors clean of dust is not easy to achieve when often changing lenses in outdoor environments with potentially not clement weather.

 

By putting in another moving element - and that's what I WAS already talking about   - you'd just increase the ammount of glass or other surfaces receiving, carrying and shaking dust inside the sensor. At one moment that mechanism has to open up - and where do you think, will the dust go then? It's not as if that mechanical element would act as dust magnet and keep the particles fixed.

 

Also, sliding doors always suffer of wear. If no dust comes from outside, little particles from the guiding elements will fall in the then difficult to clean volume in between sensor glass and "shutting curtain". I rather prefer good access to the sensor's surface and clean it from time to time. Usually these particle are only critical on bright areas with not much structure - that makes it easy to  repair.