Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Computing > Digital Photography > Canon 20D / dirty sensor / small circles within image / wait 1min to change lenses ???

Reply
Thread Tools

Canon 20D / dirty sensor / small circles within image / wait 1min to change lenses ???

 
 
MJL Photo
Guest
Posts: n/a
 
      06-03-2005
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?


 
Reply With Quote
 
 
 
 
SimonLW
Guest
Posts: n/a
 
      06-03-2005
"MJL Photo" <(E-Mail Removed)> 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


 
Reply With Quote
 
 
 
 
SimonLW
Guest
Posts: n/a
 
      06-03-2005
"MJL Photo" <(E-Mail Removed)> 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


 
Reply With Quote
 
Alfred Molon
Guest
Posts: n/a
 
      06-03-2005
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/
 
Reply With Quote
 
Jim Townsend
Guest
Posts: n/a
 
      06-04-2005
SimonLW wrote:


> 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.


Yes... It's no more than 5 volts on the CMOS sensor in the
20D.. Probably around 2 or 3.

Not only that, but the sensor is behind a mirror AND completely
covered by the shutter. (The shutter stays closed over the
sensor until it's time to take an exposure, or the sensor
cleaning function has been activated).

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


 
Reply With Quote
 
James Of Tucson
Guest
Posts: n/a
 
      06-04-2005

"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.

 
Reply With Quote
 
Mike
Guest
Posts: n/a
 
      06-04-2005

"MJL Photo" <(E-Mail Removed)> 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?
>

Sensor dust is pretty much a fact of life if you want to use a digital SLR
(and many non-SLRs as well). However, it would be a ridiculous reason for
anyone to stick with film (there are plenty of *good* reasons to do so, this
is not one). Being very fussy about lens changes will help, but you'll get a
dust speck one day. When you do, there're plenty of products on the market
to help you (some are much better than others, and all need to be used with
plenty of care so do your research.) And at the end of the day, if you've
got a couple of specks on an important image (which, by the way, usually
only show up in low-detail areas and on images taken with the lens almost
wide-open) then the healing and clone brushes in Photoshop are your
friends - nobody will ever know!!

Cheers, from somebody who *used* to sweat about sensor dust.


 
Reply With Quote
 
Skip M
Guest
Posts: n/a
 
      06-04-2005
"SimonLW" <(E-Mail Removed)> wrote in message
news:42a07ab1$(E-Mail Removed)...
> "MJL Photo" <(E-Mail Removed)> 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


 
Reply With Quote
 
James Of Tucson
Guest
Posts: n/a
 
      06-04-2005
>since the sensor is behind the
>shutter, how does dust get to it?


I suppose it wouldn't, if you never opened the shutter.

>b) wouldn't we have had dust
>problems with film, too?


We do! But the dust travels with the film, instead of staying put.

 
Reply With Quote
 
Skip M
Guest
Posts: n/a
 
      06-04-2005


"James Of Tucson" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.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


 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Big Sensor FX vs Small Sensor DX - No Diff? measekite Digital Photography 11 09-22-2008 06:36 PM
Explorer opening 1min late for the first time after windows boot, why? Gopi Computer Support 1 09-07-2007 11:05 AM
CMOS vs CCD - why Kodak has used a CMOS sensor in a small-sensor camera David J Taylor Digital Photography 4 08-15-2007 07:37 PM
Full Frame Lenses vs Small Sensor Lenses measekite Digital Photography 15 09-13-2006 03:36 PM
Ebay filling up temp Folder taking up to 1min to load CPU Usage 100% Chris Computer Support 1 05-24-2004 12:13 PM



Advertisments