Aperture Size and Sharpness

[chris]

Hey guys,

I am currently reading "The Complete Idiot's Guide to Photography Like a Pro."

While discussing "landscape mode" the author says that the camera sets a small aperture for great sharpness from foreground to background. For "portrait mode" it is the opposite.

Moreover, the author writes " in aperture priority, you set the lens aperture you want (a small one to get everything sharp from foreground to background, or a large one to throw the foreground and background out of focus)..."

Can someone please explain this relationship? ie) I do not understand how the aperture size affects image sharpness and contrast. If I have a small aperture and a slow shutter speed, will not the exposure and sharpness be the same if I use a large aperture size and a fast shutter speed?

Thanks in advance,

Chris.

[beejay]

Chris, this could be a very technically driven answer but I will deliberately keep as simple as possible. Th aperture selection detrmines the depth of field ie the distance in front of and behind the point of focus(subject) that will be rendered sharp.As you stop the the lens down, the depth of field increases, open it up and it is reduced.
To answer your second point, yes exposure will be the same but depth of field will not and this is what can give the appearance of loss or increase in contrast. but it will not alter the sharpness of the the subject you have focussed on. Also, in landscape photography time of day can determine contrast and UV content can also determine this.
Hop this helps.

[Iguanition]

On your camera, Aperture is controlled with "F-stops." Aperture works like an eye's iris. Basically, it's the hole that lets light into the camera. Have you ever tried to see something far away? What do you do with your eyes? You squint, and what you're doing is actually bending the "lens" in your eye so it has a smaller aperture.

The relationship to aperture on your camera is, as I mentioned, f-stops. The thing to remember is the larger the f-stop setting, the smaller the aperture is. This causes the depth of field to be very large, so everything is in focus. The flipside to having such a small hole, however, is that barely any light is getting into the camera.

Think of the relationship between light and aperture size as water coming out of a faucet. When the ’*‚„’‚‚’‚’‚‚‚¦‚’‚‚’‚¦’‚‚‚¦‚“hole’*‚„’‚‚’‚’‚‚‚¦‚’‚‚ ’…’‚‚� is largest, water floods out. When the hole is small, water barely trickles out. To compensate for this, you have to either set a longer shutter or change the ISO value.

I can't really give you the scientific reasons of why light acts this way. I hope this helps you out.

[wrxsavvy]

Wait Im confussed. I know that the smaller number yields a bigger aperture opening, but I thought THAT what makes everything in focus.
is my experiment wrong?

[beejay]

not quite sure what you mean there but hopefully this will answer your question:
Small F stop eg F2.8 will give larger aperture which will reduce depth of field which is area of sharpness in front of and behind point of focus.
Large F stop eg F16 will give smaller aperture which will increase depth of field again the area of sharpness in front of and behind point of focus.
beejay

[Medic1210]

Originally posted by wrxsavvy
Wait Im confussed. I know that the smaller number yields a bigger aperture opening, but I thought THAT what makes everything in focus.
is my experiment wrong?

Your example below the image is correct, along with the statement for each image that says large aperture or Small aperture. However, your actual examples in the pictures seem to be reversed. The blurred one that says Large Aperture Setting should say f/4.5, not f/29 because f/4.5 is larger than f/29. The sharp image that says Small Aperture Setting should show the value of f/29 since f/29 is smaller than f/4.5. Those are the only two reasons your example is wrong. I'm not sure why you are confused because you obviously understood that the sharper image was taken with a small aperture and the shallow DOF image was taken with a larger aperture. You only messed up when putting the aperture values in the image themselves. I'm sure that if you check the EXIF data, then you will see that you labeled them wrong. Smaller f/stop number is a larger aperture opening which gives a shallow DOF. Larger f/stop number is a smaller aperture opening which gives a greater DOF.

Mike

[wrxsavvy]

Holly crap! I had it right and someone posted

I would have said that the f2.9 setting was the bottom photo.

so I swapped the numbers around.

When its a blurred backgound that considered a "greater dof"?

Thanks for clearing up my foggy vision

I think my brain's Aperture f/stop was to low thats why its all foggy to me

[wrxsavvy]

You you know what I just noticed, he wrote 2.9 I wrote 29

hmmmmmmmm

[Medic1210]

Originally posted by wrxsavvy
When its a blurred backgound that considered a "greater dof"?

No, blurry background is shallow DOF, and an image that is clear in both the foreground and in the background is said to have a large DOF. If you see these macro images of bugs where their eye is in sharp focus and their wings is out of focus, this is a shallow DOF.

Mike

[wrxsavvy]

ahh thanks Mike