Lens Dust

[philthejuggler]

My turn for a question on optics.

I've long been a bit OCD about dust in lenses although have come to grudgingly accept dust as an inevitibility.

My question is really why doesn't lens dust make a difference in small / moderate amounts? I put my finger in front of part of a lens today and could still see stuff that should to my mind should have been blocked, instead it was simply rather feinter than without the finger, and the finger cast a haze over that part of the shot.

I guess the things are linked - does the light take many pathways throught the lens simultaneously?

Thanks

Phil

 

[Catdaddy]

<snip> does the light take many pathways throught the lens simultaneously?

In essence, yes. If you think of (for example) a pin head, the light reflected from that will be visible to the entire surface of a lens. The lens' job is then to make sure that the image is rendered in focus on the focal plane (ie the CCD) by converging all these rays of light reflected from the pin head into a single point again...

Check this link out for a simplified diagram...

http://www.howstuffworks.com/camera.htm

 

[philthejuggler]

Brilliant - thanks! That diagram explains a lot!