aperture and sharpness

[ericv]

Hi Everyone,

Thank you for looking at my post. I'm so confused here, please help. is a higher F number (smaller apeture) will give better sharpness? that's what I read and understood, but it's the other way around when it comes to my photos. i got sharpest at f8, then f13. and the higher the fnumber, my pictures are just getting more blury. (of course all other factors are being the same---I can adjust the lighing on my profoto to get higher F-number for the same amount of light).

I got a nikon D300 with the 18-55mm kit lense.

thanks a bunch for your help.

EV.

 

[tsaraleksi]

You get greater sharpness from stopping down but you have to balance that with a reasonable shutter speed, or else you're going to suffer from shake. It's all a balance.

 

[KmH]

Sharpness will also fall off at small apertures because of diffraction.

You didn't mention what you might have been doing with your ISO since it will affect shutter speed too.

 

[Dwig]

A theoretically perfect lens will be its sharpest wide open. Stopping such a lens down will only reduce sharpness. This reduction is a result of diffraction, a physical property of light that can't be altered or eliminated.

But ... nothing manmade is perfect.

Real world lenses have flaws and compromises. Some of these are more pronounced at wide apertures and can be significantly reduced by stopping down.

The end result is that real-world lenses are generally their sharpest somewhere between maximum and minimum aperture. With high quality primes, this us often 1-2 stops from maximum. With the better zooms its more often 2-3 stops down from maximum. As you stop down, the flaws and compromises have less effect and the sharpness increases. At some point, the diffraction problem becomes more significant and the flaw reduction becomes less and the sharpness decreases.

This site has an interesting interactive 3d chart that it uses in its lens reviews that gives an excellent visualization of this issue:

Camera lens tests, user reviews, camera accessory reviews - SLRgear.com!

Almost any lens review on the site, other than the "user" reviews, will have the tool. If your lens is one thats reviewed, it would be a good choice for the demonstration.

 

[Josh66]

i got sharpest at f8, then f13. and the higher the fnumber, my pictures are just getting more blury.

Most lenses are sharpest at, or near f/8. After that, sharpness starts to fall off like KmH said, and you found out.

Read this for an explaination of why it happens.

Is the camera on a tripod while you're testing this?
When you stop down a lot, you will loose a little sharpness - but it shouldn't be "blurry".

 

[KmH]

f/8 will be sharper than f/22.

Yes, the black bar is your rear (second) curtain in the frame from exceeding your sync speed.

 

[Josh66]

For this type of shot, you shouldn't really need anything more than f/8.

5.6 would probably be enough to get everything in focus...

 

[ericv]

Hi,

Thanks you guys for very usefull advises. I took some more pictures after the reading so I would love to have critics and comments from you all. These pictures were made by a nikon D300 on a prime 50mm lens. Please give me advises on lightning, sharpness, white balance...etc...

Again, thank you so much.

Great weekend.

EV

#1: F5.6-1/250s.

#2: F6.3, 1/160s

#3 F6.3, 1/200s

#4- F6.3-200-iso200