On May 9, 2004, at 4:44 AM, Carlos J. Santisteban Salinas wrote:
>
> Hi, Scott and all.
>
>> Some insist that they are caused by dirt or dust on the sensor. If
>> that
>> is the case,
>> then why are they not present in images taken with the 14-54 or 50mm
>> Zuiko
>> Digital or
>> with the OM Zuiko 65-200?
>
> A possible explanation would be the *effective* aperture on the lens.
> Dust
> on sensor will show only at small apertures, and when doing extreme
> macro,
> the *effective* aperture may be much smaller (higher f-number) than the
> setting on the lens.
>
> My 300D has also a dusty sensor :-( but is only an issue from f/16 and
> beyond, which I rarely use.
>
That is, of course, the correct explanation. The way you check for dust
is to set the lens to F16 or F22 and point it at a clear sky and take
an exposure. Then you download the picture and look at it at 100
percent. It is depth of field at the sensor plane that allows you to
see it. At wider F stops the depth of field is less and the dust is out
of focus. But it is still there. With a bellows or other type of
extension the aperture is even smaller and the dust is even more
sharply etched into your picture.
Winsor
Long Beach, California
USA
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