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Why can't dust be seen
further than a few centrimetres from the lens?
What area are we talking
about, now?
Have a look at the 'orb
zone' diagram yet again. There is a line to the
left of the subject - the person outline. This is
the 'near point of focus', meaning that everything
between the camera and that line appears out-of-focus.
Between that line and the subject/person - what you are
taking the picture of, what the camera is 'focussed' on
- everything appears in-focus.
In reality the distance of this 'line' from the camera depends on the depth of
field, which we will discuss later.
Why can't you see dust
after this line?
Because dust particles are
so tiny they are simply too small for the camera to
'see'. Dust only becomes visible when it is
out-of-focus, but more about this later.
Try it at home!
You can see a similar affect
from home. You're probably sitting in front of a
computer now. Follow these steps:
- Hold you arm out so your
hand is facing towards you and is just to the left of
your computer monitor.
- Focus your vision on the
top of your monitor - not on your hand - and you'll
probably see your hand clearly even though it's not in
your direct line of vision.
- Now keep focussing on the
top of the monitor but gradually bring your hand to the
left-hand-side of your head.
- You will see that your
hand not only looks bigger (because it's closer, of
course!) but you'll also find you'll see that after a
certain point your hand starts to look 'fuzzy' and
out-of-focus.
Whilst this is not exactly
the same as a camera operation you should see the clear
parallels.
Next Questions:
- Why is dust so big and
out-of-focus between these points?
- Why doesn't all dust
appear on camera between these points? |
