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dust problem with EOS 20Da??

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--Peter

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how will live focusing affect dust on the sensor?

because the shutter has to open for live focusing the sensor is exposed a 100 to 1000 times longer to the dusty environment per shot (assuming approx. 5 seconds for 'live' composing and focusing and choosing 1/100 for shutter speed). at what rate would the sensor collect dust? everyday sensor swabbing??

what do you think?

-- Peter
 
--Peter said:
how will live focusing affect dust on the sensor?

because the shutter has to open for live focusing the sensor is
exposed a 100 to 1000 times longer to the dusty environment per
shot (assuming approx. 5 seconds for 'live' composing and focusing
and choosing 1/100 for shutter speed). at what rate would the
sensor collect dust? everyday sensor swabbing??

what do you think?

-- Peter
Click to expand...
 
The shutter will be up yes but when would there be a situation where the lens will be off and you are snapping a picture? The dust is not going to be any more of an issue than it is right now.
 
t_fraser said:
The shutter will be up yes but when would there be a situation
where the lens will be off and you are snapping a picture? The dust
is not going to be any more of an issue than it is right now.
Click to expand...
why no difference?

there is much more time (seconds!) for the dust to go and sit on the sensor/AA filter. how far does a dust paritcel move in 1/250 second vs. 10 seconds? the sticky ones will sure stay on the sensor...

-- Peter
 
The point is dust is normally only an issue during lens changes. Do you think if you do long exposure shots you have more dust than normal shots? I dont. I do think if you decided to pull your lens off during a live preview shot you will have a problem but otherwise no difference.

Tom
 
So we need to get our cams perfectly clean then put on the ultra light 10-800 f/1.0 :> )
 
--Peter said:
how will live focusing affect dust on the sensor?
Click to expand...
It won't because there will be a lens blocking the dust.
--Peter said:
because the shutter has to open for live focusing the sensor is
exposed a 100 to 1000 times longer to the dusty environment per
shot (assuming approx. 5 seconds for 'live' composing and focusing
and choosing 1/100 for shutter speed). at what rate would the
sensor collect dust? everyday sensor swabbing??

what do you think?

-- Peter
Click to expand...
I just hope Canon comes out with an updated firmware to allow a "live mode" with the 20D.
 
David Schlanger said:
And how would it work? Mirror lock-up all the time during live
mode? Because the mirror of the 20D is not semi-transparent...
Click to expand...
Yes it is. That's how the focus sensors get their light. But I don't think the back mirror is semi-transparent. Probably the 20Da either flips the back mirror out of the way during live preview thereby eliminating AF or that mirror is semi-transparent too which means the AF will need more light to work when not using live preview.

Unless I don't understand something, there is a tradeoff for this capability.

Lee Jay
 
The 20Da mirror is semi-transparent, which would also lose light to the reflex viewing system. There may be other tradeoffs as well.

There Ain't No Such Thing As A Free Lunch. If there were no disadvantages to ordinary picture taking, this would not be released as special use product.

--
RDKirk
'TANSTAAFL: The only unbreakable rule in photography.'
 
it's all in manual mode, including and especially MF, so probably mirror lock-up:

http://www.canon-sales.co.jp/camera/eosd/20da/special/index01.html

so it IS a specialty thing, for sure.

-- Peter
ljfinger said:
David Schlanger said:
And how would it work? Mirror lock-up all the time during live
mode? Because the mirror of the 20D is not semi-transparent...
Click to expand...
Yes it is. That's how the focus sensors get their light. But I
don't think the back mirror is semi-transparent. Probably the 20Da
either flips the back mirror out of the way during live preview
thereby eliminating AF or that mirror is semi-transparent too which
means the AF will need more light to work when not using live
preview.

Unless I don't understand something, there is a tradeoff for this
capability.

Lee Jay
Click to expand...
 
--Peter said:
how will live focusing affect dust on the sensor?
Click to expand...
Compared to the actual exposures of (multiple) minutes, the couple of dozen seconds to focus the telescop on the sensor is of little concern.

Refractor and Catadioptric telescoper (SCTs and MCTs) have closed optical tubes, and the dust problem here is similar to regular camera lenses. However, big Newtonians do not have closed optical tubes and do have a problem with dust. However, most SLR to telescope adapters (T-ring+1.25 or 2.0 focuser adapter) are fitter with threads for 48mm filters, so the camera operator can take proactive steps to minimize the entry of dust.

What concerns me is that using the LCD to focus the telescope will invariably use the sensor in a repetative fasion, readout-> A/D, reset :: repeat until the camers is directed to do otherwise. This will heat up the sensor and heat up the A/D--the last thing you want to happen to the camera just before beginning a long astroimage.

--
Mitch
 
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