Understanding Aperture...

[Mickey Fliers]

So this is turning into Photography 101 for Mickey Fliers, so I hope you all don't mind.

Okay, Aperture. If I only want the subject in focus, while the background is out of focus, I would choose a wide aperture, which is a small "f" number, correct??

And then of course the opposite would be true. A high "f" number would produce a pic where there is a large depth of focus.

So, f3.2 would only focus on the subject, while f8 would focus on everything.

Do I have this right?

TIA...

More questions to follow, I am sure

 

[YEKCIM]

Generally speaking, that is correct. There is one more variable to consider, and that is the lens focal length. At a wide setting, no matter what aperture you use, more is going to be in focus, due to greater depth of field. Using a telephoto focal length will result in shallower depth of field, even using a smaller (higher number) aperture.

Here's a picture of a bust of Mickey's dad, that illustrates what I mean:

The focal length was almost at the end of the zoom range, and that, along with a relatively wide aperture, is what separates the subject from the background.

That make sense?

~YEKCIM

 

[MICKEY88]

So this is turning into Photography 101 for Mickey Fliers, so I hope you all don't mind.

Okay, Aperture. If I only want the subject in focus, while the background is out of focus, I would choose a wide aperture, which is a small "f" number, correct??

And then of course the opposite would be true. A high "f" number would produce a pic where there is a large depth of focus.

So, f3.2 would only focus on the subject, while f8 would focus on everything.

Do I have this right?

TIA...

More questions to follow, I am sure

basically yes, + a telephoto lens will have more effect than a short lens such as a 50mm..

 

[Mickey Fliers]

Great, absolutely makes sense. I may be getting the hang of this thing after all .

 

[handicap18]

Took me a while to get it too. And that was even after 3 semesters of photography in high school. Granted that was about 20 years ago.

The f in the "f-stop" stands for focal length. The whole f/2.8 thingy is actually an algebra equation. The math determines how wide the actual hole is. This determines how much light is allowed to pass to the film/sensor. So 50mm lens divided by 2.8 = 17.9 mm aperture opening. 50mm lens divided by 1.8 = 27.8mm aperture opening. 50mm lens divided by 5.6 = 8.9mm aperture opening, etc...... More light that is allowed in will give less focus beyond what the lens is actually focusing on. The less light that is let in will give more sharpness to that beyond what the lens actually is focusing on. Kind of like when you see someone, who is supposed to wear glasses but forget them, squinting to see something clearer.

 

[boBQuincy]

Kind of like when you see someone, who is supposed to wear glasses but forget them, squinting to see something clearer.

Great analogy, and very meaningful to me!

I am fascinated by the technical ideas behind photography. To carry the f stop technical data further, only one plane is ever in focus, the rest of the image is in varying degrees of non-focus described by "circles of confusion" (no, I didn't make that up).
As the circles get smaller (from a smaller aperture), more of the image appears to be in focus.

On a P&S camera the lens actually has a very short focal length and even at f/3.2 much of the image appears in focus, especially at the wide angle range.

 

[MarkBarbieri]

Another thing to remember about your aperture is the affect on sharpness. Most lenses are significantly sharper when stopped down a couple of stops. Shot wide open (minimum f-stop), they get soft.

Another issue is diffraction. If you stop a lens down too much, you lose sharpness because of diffraction. Even though a shot taken at f22 might have greater depth-of-field than one taken at f11, it is likely to be less sharp. If everything you need is in focus at f11, you’re better off shooting there.

Each lens/body/sensor combination is different, but typically the sweet spot for most lenses is somewhere between f8 and f11. Of course, if you composition calls for extremely shallow or deep depth-of-field, you’ll have to make trade-offs.

 

[jann1033]

T Kind of like when you see someone, who is supposed to wear glasses but forget them, squinting to see something clearer.

finally something i can relate to

? how do you know the "sweet spot" for your lens,,trial and error, more math( )

i just got this yesterday, good newsletter for those less "photo-genius" ly inclined like me

http://digital-photography-school.com/blog/aperture/

and spiffy newish download for dof from tamron europe

http://www.tamron.de/Depth_of_Field_Comparison.289.0.html?&L=2

 

[MarkBarbieri]

The most accurate way to know how sharp your lens is at different apertures (and focal lenghts) would be to do lots of tests. I'm way to lazy for that. I just use f8 to f11 when depth of field and shutter speed aren't an issue. When I want to open up or stop down past that, I sometimes ask myself whether I need to or whether adjusting some other parameter (ISO, shutter speed) would be better.