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Archive 2005 · "Neutral" t/c to prevent sensor dust?
  
 
HiltonP
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p.1 #1 · p.1 #1 · "Neutral" t/c to prevent sensor dust?


A question for the Canon technical fundi's . . . Given the challenge we face with sensor dust, is it possible to make a "dummy", or "neutral" tele-converter type of attachment for the camera? It would stay "permanently" in place (removed only when needed), effectively sealing off the mouth of the dSLR. It would provide no magnification (hense the neutral) and the minimum of glass between the lens and the sensor. Lenses could then be changed at will, without the inside of the camera being exposed to the outside air.

I know users of traditional 1.4x and 2x t/c's are already using this principle, it works well in dusty environments like Africa and Asia. I'm essentially thinking of a 1.4x t/c, but without the magnification, and with the minimum of glass.



Apr 22, 2005 at 01:44 PM
david010167
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p.1 #2 · p.1 #2 · "Neutral" t/c to prevent sensor dust?


an interesting and simple idea. So my question would be; why would this not have been done? Why does having access to mirror give anything to the photog, the exception being those cameras that can change the focus screen.

regards

David



Apr 22, 2005 at 01:51 PM
moondigger
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p.1 #3 · p.1 #3 · "Neutral" t/c to prevent sensor dust?


1. It would have to have at least some small amount of magnification, since without it the lens would not be able to focus at infinity. i.e., a plain flat glass piece would still move the lens away from the sensor plane by some small amount, and only lenses designed to focus past infinity would be able to attain infinity focus.

2. The "converter" you're talking about would have to be in front of the mirror but behind the rearmost extension of any lens that might be used... since some lenses recess into the camera body fairly close to the frontmost extension of the moving mirror, I don't think it would be possible.

3. Even if such a piece could be designed/used, it would increase the likelyhood of flare. More air/glass surfaces means more opportunity for image degradation.



Apr 22, 2005 at 01:56 PM
uz2work
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p.1 #4 · p.1 #4 · "Neutral" t/c to prevent sensor dust?


I think that the idea, at first consideration, has merit, but I think that the theory is that going through another piece of glass is going to, even in a very minor way, cause some deterioration in image quality and that most would prefer to deal with the minor irritation of getting dust on the sensor as opposed to paying the price of even minor loss of image quality.
Les



Apr 22, 2005 at 01:58 PM
pscard
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p.1 #5 · p.1 #5 · "Neutral" t/c to prevent sensor dust?


It would function the same as an extension tube if the 1X TC did not have some form of corrective (magnifying) element.


Apr 22, 2005 at 02:02 PM
 

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HiltonP
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p.1 #6 · p.1 #6 · "Neutral" t/c to prevent sensor dust?


Positioning relative to the mirror isn't an issue since existing t/c's work fine in this regard.

Surely any possible distortion (or degradation) or quality would be minimal with a neutral, flat glass plane. Current degradation from 1.4x and 2x t/c's is largely due to their magnification factor. If these were 1x, or neutral, it would be minimal?



Apr 22, 2005 at 04:30 PM
JVasek
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p.1 #7 · p.1 #7 · "Neutral" t/c to prevent sensor dust?


I think 'moondigger' is correct that the converter would need magnification, but I think its less than 1.0x in order to bring the infinity focus back to the 'sensor' plane without affecting the local length.

In simplistic terms I see that the sensor already has a piece of glass (or whatever) there called the anti-aliasing filter assembly maybe if it was made more scratch resistant and easier to clean that's sufficient ?



Apr 22, 2005 at 04:48 PM
nutek
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p.1 #8 · p.1 #8 · "Neutral" t/c to prevent sensor dust?


Another idea would be to have some kind of protective curtain that chomps down when you unmount a lens. I believe it has been talked about before, but why it hasn't been implemented yet remains a mystery


Apr 22, 2005 at 05:59 PM
moondigger
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p.1 #9 · p.1 #9 · "Neutral" t/c to prevent sensor dust?


HiltonP wrote:
Positioning relative to the mirror isn't an issue since existing t/c's work fine in this regard.


Existing TCs magnify the image, and are designed to work with lenses that don't have rear elements which recess into the camera body. The proposed "neutral" TC would be a flat piece of glass, with a mount thick enough to accept the lens attaching to it. That mount would move the lens forward like an extension tube, and would result in a loss of infinity focus.

Now consider what to do with lenses that have rear elements that protrude into the camera body? Existing TCs are not compatible with these (typically wide-angle) lenses. So for a "neutral" TC to work with them, it couldn't just be a flat piece of glass. It would have to recess into the camera body in such a way as to accept lenses with protruding rear elements. Either that, or it would have to employ an even thicker mount, to move the lens even further away from the camera body, just to get these lenses to mount. And once you've moved those lenses that far away from the camera body, they may not be able to attain any focus whatsoever, much less infinity focus.

Surely any possible distortion (or degradation) or quality would be minimal with a neutral, flat glass plane. Current degradation from 1.4x and 2x t/c's is largely due to their magnification factor. If these were 1x, or neutral, it would be minimal?

Surely any degradation of image quality would be less due to minor dust accumulation on the sensor than it would be with an additional piece of glass and the loss of infinity focus.



Apr 22, 2005 at 06:14 PM







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