Re: Keeping the Canon 300D Rebel EOS Dust Free

From: Wade A. Hilmo (wadeh_at_blarg.net)
Date: 01/24/05 

Date: Mon, 24 Jan 2005 08:46:05 -0800

Depending on the shots you take, dust on the sensor of a DSLR can be a huge
deal.

It's not actually on the sensor, though. The sensor is actually sealed
behind a number of optical layers (like the IR filter and byers mask.) The
dust actually collects on a plate of glass a small distance away from the
sensor.

Because the dust is not directly on the sensor, the focal ratio at which you
are shooting will affect whether the dust will be in focus or not. At fast
focal ratios, say F10 or faster, you generally don't see the dust, unless
there is a really huge chunk of something on the sensor. If you shoot at
much higher focal lengths, then it is very apparent.

Here is an experiment you can try (warning - don't do this if knowing about
dust in your images will bother you.) Put a terrestrial lens on the camera
and set it up for aperture priority. Set the highest focal ratio you can -
at least F20, but F30 or more would demonstrate better. Now lock the focus
on a distant object and then take a picture of an evenly lit part of the
sky. You are almost guaranteed to see dust spots in the image. If you have
not cleaned the sensor in a few months, you will probably see a whole lot of
dust.

If you usually use faster focal ratios in your shots, then you don't really
need to worry about this. If you are doing astrophotography, then flat
frames will take care of any dust spots.

If you have dust spots that are big enough to show up in terrestrial
photography using a fast focal ratio, then using a blower should work.

If you want to make the rest of the dust go away, then the only way to do so
without voiding the warranty on the camera is to have it cleaned by an
authorized dealer. If you want to clean the sensor yourself, there is a
cottage industry springing up around doing this. A quick search on
something like 'clean dslr sensor dust' will give you plenty of reading.
Note that if you scratch or otherwise damage the sensor while doing this
yourself, it will definitely not be covered under warranty.

Thanks,
-Wade

"Chris L Peterson" <clp@alumni.caltech.edu> wrote in message
news:v56av011jndrliuavuue7tgntg6as3pe5m@4ax.com...
> On Mon, 24 Jan 2005 15:37:14 GMT, "W. Wat son" <wolf_tracks@invalid.inv>
> wrote:
>
> >Fortunately, I don't have the problem in the title, but a friend
cautioned
> >me about it through an experience a colleague of his had. The story is
> >this. If you take your lens off, make sure that you turn the power off.
> >Apparently, the static charge on the chip can more easily attract small
> >particles when charged, and it is very difficult to get to the mirror to
> >clean it. Further, he said cleaning the mirror can be a real problem. His
> >colleague experienced this problem when he repeatedly had to change
lenses
> >in a short time (several hours). So is this anecdontal or is there some
> >basis in fact for the claim?
>
> I'd say this is nonsense. CCD and CMOS sensors operate at very low
> voltages- they don't develop static charges on the cover glass as a
> result of being operated. And even if they did, static charges are
> difficult to remove from insulators- simply turning off the power isn't
> going to make the charge dissipate.
>
> A dirty mirror is not of much concern since it has no impact on the
> images. If it gets dusty enough it might be irritating to use the
> viewfinder, but that's all. Dust on the cover glass of the sensor will
> show up on images, but that doesn't happen too often- it is protected by
> the shutter. I see a bit of fluff show up once a month or so (and I use
> the camera daily, and change lenses often). I just keep a little can of
> air in my bag to blow off the sensor (and mirror) when that happens. No
> big deal.
>
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com

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