Aperture question

jazzywheelz

jazzywheelz

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James
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I know that aperture controls depth of field, but are there any other effects (however subtle) of altering aperture?

For example, imagine shooting a completely flat wall, head on, with nothing else in the frame (ie. no depth of field). Would a shot at 1/500s f/5.6 look exactly the same as a shot at 1/15s f/32 (assuming no movement or changes in lighting etc.) ?

I think I know the answer, but just need to settle my overactive mind lol :nuts:
 
The shot at 5.6 will be sharper because as you stop down you have diffraction to consider. Most lenses start to exhibit this at around f10.
 
Diffraction isn't a property of the lens as such. It's a property of light and how it squeezes through the hole :D and is made more visible (or less visible) depending upon resolution and image size and viewing distance and stuff like that :D

Try to keep in mind that there's no point using an aperture that'll give you more DoF than your scene requires.
 
jazzywheelz said:
For example, imagine shooting a completely flat wall, head on, with nothing else in the frame (ie. no depth of field). Would a shot at 1/500s f/5.6 look exactly the same as a shot at 1/15s f/32 (assuming no movement or changes in lighting etc.) ?
Click to expand...

Both shots could look less than the best possible image :'( The f5.6 could look less than its best if the lens is wide open, most lenses are at their best when stopped down a little, and the f32 shot will probably look less than its best because of diffraction and loss of contrast and dynamic range.
 
Main changes with higher f/number:

More depth of field.

Sharpness - at lowest f/number, aberrations reduce sharpness particularly around the edges. Most lenses peak around f/5.6 to f/8. Then diffraction takes over and sharpness falls across the whole image. It's noticeable at f/11, gets worse at f/16, f/22 should be avoided if at all possible and f/32 would be horrendous on a DSLR though diffraction varies acording to format (which is why many compacts don't go higher than f/5.6).

Vignetting (darkening of corners) is reduced, though it's usually gone by f/5.6-8.

Aperture shape can change the look out out of focus highlights and can promote star-shaped specular highlights.

Usually less flare (higher contrast).

NB Distortion doesn't change with aperture.
 
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Blimey! :eek:
So there really is a fair bit more to consider than I thought.
That lot is going to take some digesting. I'm a complete beginner and only just getting my head around what aperture to use in different situations.
Looks like I've got some studying to do :geek:
Thanks for the replies guys :thumbs:
 
jazzywheelz said:
Blimey! :eek:
So there really is a fair bit more to consider than I thought.
That lot is going to take some digesting. I'm a complete beginner and only just getting my head around what aperture to use in different situations.
Looks like I've got some studying to do :geek:
Thanks for the replies guys :thumbs:
Click to expand...

Not really. Stick with changes to depth of field - that makes ten times more difference than anything else. And don't use f/32!
 
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