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The three things that annoy my with digital

 
 
~Darrell Larose~
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      10-07-2004
<(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> In message <(E-Mail Removed)>,
> "BG250" <(E-Mail Removed)> wrote:
>
> >I have the dRebel, but I actually never had dust spots yet. I'm very

careful
> >to keep it capped or have a lens attached. I point the camera down to

change
> >lenses. I try to keep the camera bag clean. It has worked so far, but I'm
> >sure dust will get in at some point.

>
> If you're not shooting simple textures like blue sky at tiny apertures,
> you may not notice the dust. At larger apertures, dust may only slighty
> darken a wide area around the particle and slightly lower the contrast;
> virtually imperceptible.
> --


Why would a small aperture show dust better than a large aperture?


 
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Bill Hilton
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      10-07-2004
>From: "~Darrell Larose~" http://www.velocityreviews.com/forums/(E-Mail Removed)

>Why would a small aperture show dust better than a large aperture?


Depth of field
 
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Dave Martindale
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      10-07-2004
"~Darrell Larose~" <(E-Mail Removed)> writes:

>Why would a small aperture show dust better than a large aperture?


The dust is on a glass window above the sensor, not on the sensor
surface itself. Thus, the shadow cast by the dust is affected by the
steepness of the cone of light from the lens. With a small aperture
(f/22) the lens acts as nearly a point source (rather like the sun on a
clear day) and casts hard-edged dark shadows, making the dust visible.
A large aperture gives a large cone of light converging on each point on
the sensor, and it gives a soft diffuse shadow (rather like the shadows
from an overcast sky) that may not be visible at all.

Dave
 
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JPS@no.komm
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      10-07-2004
In message <(E-Mail Removed)>,
"~Darrell Larose~" <(E-Mail Removed)> wrote:

><(E-Mail Removed)> wrote in message
>news:(E-Mail Removed).. .
>> In message <(E-Mail Removed)>,
>> "BG250" <(E-Mail Removed)> wrote:
>>
>> >I have the dRebel, but I actually never had dust spots yet. I'm very

>careful
>> >to keep it capped or have a lens attached. I point the camera down to

>change
>> >lenses. I try to keep the camera bag clean. It has worked so far, but I'm
>> >sure dust will get in at some point.

>>
>> If you're not shooting simple textures like blue sky at tiny apertures,
>> you may not notice the dust. At larger apertures, dust may only slighty
>> darken a wide area around the particle and slightly lower the contrast;
>> virtually imperceptible.


>Why would a small aperture show dust better than a large aperture?


The larger aperture allows light to strike the sensor underneath the
dust from wider angles, giving a larger, softer penumbra.

It's like the difference between the shadow cast by a large flourescent
lightbulb, and an arc-lamp.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <(E-Mail Removed)>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

 
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