Understanding aperture

Sask2005

I am embarrassed to ask this but at least I don't have to show my face.

I can never remember DOFs, apertures etc

My question:

If f22 is a tiny opening in the iris why does it allow a very deep DOF?

:scratch:scratch:scratch

Andy

Sask2005 wrote:

I am embarrassed to ask this but at least I don't have to show my face.

I can never remember DOFs, apertures etc

My question:

If f22 is a tiny opening in the iris why does it allow a very deep DOF?

scratch

http://en.wikipedia.org/wiki/Aperture
http://www.photo.net/learn/making-photographs/exposure

Shay Stephens

Think of the difference between the sharpness of a shadow when the light source is a distant bare light bulb versus the soft diffuse shadow created by a close lamp with a big white lampshade.

The sharp shadow created by the faraway light bulb is caused by the light rays being largely parallel to each other. And that is what a small aperture like f/22 does, it forces the light to be more directional. A wide open aperture like f/2.8 allows the light to be more loosy-goosy.

A laser, forcing the light to bounce back and forth in it's laser tube and be super directional and parallel, is somewhat like using a small aperture like f/22. The pencil thin beam goes the farthest of all the light sources.

agunther

Let me add to that list:
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm
http://www.cambridgeincolour.com/tutorials/hyperfocal-distance.htm
http://www.cambridgeincolour.com/tutorials/camera-lenses.htm
(its one of my favorite site when it comes to technical stuff)
Whats really cool is their calculators.

cmason

If you want to see things in the distance, what do you normally do?

Squint your eyes, right? That essentially makes the opening to your eye smaller, bringing things in the distance into focus. So smaller aperture = distance in focus.

The only thing left to remember is that a high f# is a smaller opening. This used to be easier with manual lenses, as you only had to look at the back of the lens as you turned the apeture ring to 'get it".

Sask2005

Thanks everyone. I think I have got it now!