Re: DUST: Does this rule out buying DSLR's?


"Kennedy McEwen" <rkm@xxxxxxxxxxxxxxxxxx> wrote in message
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In article <43f812e4$1@xxxxxxxxxxxx>, Jim F B <jimfb@xxxxxxxxx> writes

"Kennedy McEwen" <rkm@xxxxxxxxxxxxxxxxxx> wrote in message
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In article <43f6a589$1@xxxxxxxxxxxx>, Jim F B <jimfb@xxxxxxxxx> writes

In the site referred to below it says that the fixed lense Sony DSC-R1
has
a
SEALED sensor, so therefore there are NO dust problems.

Well that is a non-sequitur since the sensors on *all* digital cameras
use
sealed sensors, yet most dSLRs still get dust problems. The sensors are
all in hermetic packages with at least a cover glass window and usually
an
AA filter as well. Not one single camera on the market permits access
to
the sensor itself, since its surface is much more fragile than you could
imagine. Those colour filters in the Bayer array, for example, are
extremely soft and would be wiped off by most of the recommended
cleaning
techniques and dissolved by many of the cleaning solvents used! I
couldn't imagine running a Pecpad across a dSLR *sensor* without
damaging
it.

You say that most dSLRs still get dust problems. So, by inference, the
conclusion in the review of the permanently mounted lense camera, the Sony
DSC-R1, that it has no dust problems, would be a fair one? I guess that
extremely few (if any) digital cameras that have permanently mounted
lenses
would get dust on their sensors?

Not necessarily - all cats are four legged mammals, but all four legged
mammals are not cats. Just because most dSLRs get dust problems doesn't
mean that most fixed lens cameras don't. They are certainly less likely
to get it but, as others have pointed out in the thread, its much harder
to get rid of when they do.

It seems, however, that dust on the sensor of a fixed lense camera is so
RARE that the occurrence rate would probably be as low as 1 in 100,000
digital cameras. But the more you look back on newsgroup postings on this
issue, the more you see how MOST DSLR owners find it an extremely irritating
thing, because dust problems arise with ALL DSLRs. Here's a posting I found
on the sci.astro.amateur newsgroup. This poster considers that, depending on
the shots you take, dust on the sensor of a DSLR can be a "HUGE" issue. Wade
raises an interesting issue about voiding the warranty with regard to
attempts to clean the sensor. I think all DSLR users need to be very clear
on how their manufacturer's warranty deals with this issue before they
attempt to remove dust from the sensor.

From: Wade A. Hilmo - view profile
Date: Tues, Jan 25 2005 5:46 am
Email: "Wade A. Hilmo" <w...@xxxxxxxxx>
Groups: sci.astro.amateur
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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




.

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