Canon 20D / dirty sensor / small circles within image / wa..

Archived from groups: rec.photo.digital (More info?)

"MJL Photo" <mjlphotographics@shaw.ca> wrote in message
news:bgTne.1556107$8l.842610@pd7tw1no...
> SITUATION:
> There is small circles with a pin point in the centre of each appearing
> within all images taken.
> Could this be a sign of a dirty sensor?
>
> RECOMMENDED:
> This friend of mine (i am still using film) uses the 20D and was told by
the
> shop owner to wait 60 seconds after taking a photo before changing lenses.
> The reasoning behind this was that the sensor still holds a (possible
> electro magnetic) charge for a short time after taking a photo.
> Could removing the lens directly after the shutter allow dust particles to
> enter and adhere to the sensor?
>
> If this is truely the recommended way of changing lenses, I think I will
> stick with film until snesor cleaning is more user-friendly.
>
> This all sounds very odd, but is it possible???
>
> Any comments?
>
>
Yes, that static charge created by the sensor stuff I keep hearing about is
utter nonsense. Only very low logic level voltages are used on the CCD. It
is nothing like the old camera tubes that have a few thousand volts on the
anode. The dust lands on the sensor as it does other surfaces like the
mirror or the side of the mirror box. The less time the mirror box is open
(no lens attached) the better the chances for dust entry. Changing lenses
outside on a windy day is likely going to get some dust inside. Some Olympus
cameras us ultrasonics to vibrate the dust off the sensor. I don't know how
effective it is.
-S

Archived from groups: rec.photo.digital (More info?)

In article <bgTne.1556107$8l.842610@pd7tw1no>, MJL Photo says...
> SITUATION:
> There is small circles with a pin point in the centre of each appearing
> within all images taken.
> Could this be a sign of a dirty sensor?
>
> RECOMMENDED:
> This friend of mine (i am still using film) uses the 20D and was told by the
> shop owner to wait 60 seconds after taking a photo before changing lenses.
> The reasoning behind this was that the sensor still holds a (possible
> electro magnetic) charge for a short time after taking a photo.
> Could removing the lens directly after the shutter allow dust particles to
> enter and adhere to the sensor?
>
> If this is truely the recommended way of changing lenses, I think I will
> stick with film until snesor cleaning is more user-friendly.

Well, there is the Olympus E300 DSLR which every time you switch on the
camera automatically cleans the CCD (inbuilt supersonic wave cleaner).
--

Alfred Molon
------------------------------
Olympus 4040, 5050, 5060, 7070, 8080, E300 forum at
http://groups.yahoo.com/group/MyOlympus/
Olympus 8080 resource - http://myolympus.org/8080/

Archived from groups: rec.photo.digital (More info?)

"With the mirror AND shutter in the way, dust would have a tough
time finding the sensor. "

It gets there, though. Doesn't seem to have a hard time at all. Even
if you keep your lens changes short, and are fastidious about where you
do the changes.

OTOH, I haven't yet seen dust that wasn't easily abated by blowing it
with a bulb blower.

Archived from groups: rec.photo.digital (More info?)

"SimonLW" <anon@anon.com> wrote in message
news:42a07ab1$1_5@newsfeed.slurp.net...
> "MJL Photo" <mjlphotographics@shaw.ca> wrote in message
> news:bgTne.1556107$8l.842610@pd7tw1no...
>> SITUATION:
>> There is small circles with a pin point in the centre of each appearing
>> within all images taken.
>> Could this be a sign of a dirty sensor?
>>
>> RECOMMENDED:
>> This friend of mine (i am still using film) uses the 20D and was told by
> the
>> shop owner to wait 60 seconds after taking a photo before changing
>> lenses.
>> The reasoning behind this was that the sensor still holds a (possible
>> electro magnetic) charge for a short time after taking a photo.
>> Could removing the lens directly after the shutter allow dust particles
>> to
>> enter and adhere to the sensor?
>>
>> If this is truely the recommended way of changing lenses, I think I will
>> stick with film until snesor cleaning is more user-friendly.
>>
>> This all sounds very odd, but is it possible???
>>
>> Any comments?
>>
>>
> Yes, that static charge created by the sensor stuff I keep hearing about
> is
> utter nonsense. Only very low logic level voltages are used on the CCD. It
> is nothing like the old camera tubes that have a few thousand volts on the
> anode. The dust lands on the sensor as it does other surfaces like the
> mirror or the side of the mirror box. The less time the mirror box is open
> (no lens attached) the better the chances for dust entry. Changing lenses
> outside on a windy day is likely going to get some dust inside. Some
> Olympus
> cameras us ultrasonics to vibrate the dust off the sensor. I don't know
> how
> effective it is.
> -S
>
>
This may seem like a silly question, but since the sensor is behind the
shutter, how does dust get to it? If the sensor were that permeable to
dust, a) wouldn't it be permeable to light, and b) wouldn't we have had dust
problems with film, too?
I've wondered this for some time, now...

--
Skip Middleton
http://www.shadowcatcherimagery.com

Archived from groups: rec.photo.digital (More info?)

"James Of Tucson" <james0tucson@gmail.com> wrote in message
news:1117898487.788599.157180@g49g2000cwa.googlegroups.com...
> >since the sensor is behind the
>>shutter, how does dust get to it?
>
> I suppose it wouldn't, if you never opened the shutter.

Then changing a lens wouldn't make any difference, would it? I mean, if the
shutter is closed when you change lenses, how is changing lenses responsible
for dust getting in? And if there is a lens mounted, and dust still gets
in, why is everyon so careful when changing lenses?

>
>>b) wouldn't we have had dust
>>problems with film, too?
>
> We do! But the dust travels with the film, instead of staying put.
>
I never had dust get on film in camera, just in the lab. Of course, that
little fuzzy strip on the canister probably did an admirable job of keeping
the dust out, now that I think of it...

--
Skip Middleton
http://www.shadowcatcherimagery.com